Even though I know the relativistic effects of gravity differences, it never occurred to me that the earths core would, in fact be younger because of this. Gosh, darn it do I love Physics!
Since the core is very hot, all the particles within the core are moving much faster. Would this contribute to the age difference due to special relativity considerations?
But because it is solid, the age dilation from the gravitational field will be far greater than any "savings" via special relativity. It would need to be moving fast enough to break its structure in order to dominate the equation.
Time dilation due to movement does not require a particle to be moving in one direction. Hotter particles are absolutely moving faster, even if that's just the brownian motion of heat within a solid structure. I think his idea has merit. This would make the core younger past the 2.5 years.
I did consider it, and I gave a quick judgment response as we are comparing 5000C to 3500C - 1000C depending on where we're measuring. It isn't enough of a delta to compensate for the time dilating effects of gravity.
Could something similar be said for any sufficiently large object? For instance, could the atoms in an apple core be zeptoseconds younger than its skin?
Given all mass produces* a gravitational field, I don’t see why not, but you’re probably quite a few orders of magnitude off.
\*not sure *exactly* what the relationship is
Does time dilation depend on potential/force, or something else?
If you're a particle in the core, the only (newtonian) gravitational force you experience is due the mass that's beneath you as the larger sphere does not influence you. As such, the acceleration due to gravity would be much lower there I presume.
But if that is not how it works, and all of the mass contributes, then the time dilation should be undefined (tending to infinity as you go closer to the core) exactly at the core, right?
Hang in, in Newtonian gravity any thing at the centre of a mass would experience no gravity. I imagine the same would be true in general relativity. So wouldn’t that mean there’s no time dilation at the core, but it’s the mantle which is younger?
The Leidenfrost effect allows a person to plunge their fingers into molten lead* and remove them unscathed. A thin layer of water essentially forms a protective barrier on the surface of the fingers.
*Under very specific circumstances, do not try at home
This also works with molten iron and rock, if the viscosity is low enough. If the viscosity is not low enough then you get a much more exciting, if less entertaining result.
Also works with liquid nitrogen - I have plunged my hand into liquid nitrogen (and took it out quickly!) as well as put some on my tongue for a cool (no pun intended) effect.
Stars have negative heat capacity. If you'd put them into a giant oven, they would actually cool down (however they would expand, thus storing the additional energy emitted from the oven in the form of potential energy)
Also, last I checked, hypergiant stars have density less than our atmosphere. Not sure if smaller stars do as well but I think the hotter they get the more they puff out.
Also for black holes, their mass is proportional to their schwarzchild radius, so if you say they have a density defined by the volume in their event horizon, they get far less dense as they get more massive. Although that may be an absurd metric and who knows if that equation for radius really is accurate.
Isn't this only for white dwarfs? I hear they maintain their shape due to Fermi Degeneracy pressure only. Do regular stars also have states filled all the way up?
Uh, it was an exercise for an astrophysics exam in my undergrad a couple years ago. If I remember correctly, it was an application of the virial theorem (https://en.wikipedia.org/wiki/Virial_theorem?wprov=sfla1) on a gravitational bound gas cloud, but don't quote me on that, it is not my area of expertise any more. Most importantly I remember the result, we discussed it broadly in our exercise class and it blew everyone's mind, even the tutor got excited about it!
Skimming over the Wikipedia article I shared, this is exactly the case for cores of stars, even off the main sequence. I remember having vivid thought experiments for a couple of weeks just to wrap my mind around this! Such a fascinating topic in physics.
Thanks I’ll have to try it out, I know for blackholes it’s super easy once you have the entropy. My first thought was “stars are just balls of gas, why would they behave differently”, but now I’m thinking it’s probably due to gravity. Wonder if I could just add a gravitational term to the Hamilton, construct the partition function and determine entropy…
If viewed through sufficient length (one or two meters at least), water appears blue, not clear. This is mostly because the energy associated with vibrational frequency transitions of water molecules absorbs light in the red end of the visible EM spectrum more than the violet end. Heavy water (deuterium oxide), however, is clear, because the absorption spectrum is shifted into the infrared due to its heavier hydrogen atoms.
Also, I don't know if this has been tested before, but in theory, because spectral bands undergo broadening at higher temperatures and one of the absorption bands of water is just barely outside the visible part of the spectrum in the infrared unless it is broadened sufficiently, hot water should be more blue than cold or room temperature water.
When SCUBA diving, you can see all the colors fall off as you go deeper. Red goes away in only a few feet, it seems like. Down deep, 30+ meters, everything is almost greyscale in blue - that is, until you bring out a dive light.
[Hot water should indeed be bluer](https://www.researchgate.net/figure/Pure-water-absorption-spectra-measured-as-a-function-of-temperature-15-65-C-The_fig3_44676498)
The key part is actually the 650-750 nm region which is safely visible but a bit hard to see on the original plot, which is also weakly [increasing with temperature](https://imgur.com/a/RsoCBLJ) (This paper uses the arrow to point in direction of decreasing temperature for some reason). This region is also the most [significant visible absorption](https://www.researchgate.net/figure/Absorption-coefficient-of-visible-light-in-water-2_fig1_316232236) for water.
That's all I was going on before but [this paper](https://opg.optica.org/ao/viewmedia.cfm?uri=ao-36-24-6035&seq=0) also reports no significant temperature dependent absorption for water outside this band and its next overtone in the visible (unfortunately no pretty plots).
My favorite is the principle of least action. All of newtons laws can be developed from one principle: that the path an object takes through space will be the one such that the transfer from potential to kinetic energy along its path will be a minimum. Its hugely important in quantum mechanics and is mostly not mentioned in undergraduate physics.
It’s actually the principle of stationary action as sometimes the solution is a maximum or an inflection point (the most common examples are in optics when looking at the path of light in strange circumstances - like concave mirrors or materials with negative refractive indexes). It’s unhelpful things like that which make it less popular to reach to undergrads unless they’re specialising in an area like particle physics where Lagrangians turn up a lot
You could also say that it's the principle of locally minimized action, where the action is minimized over short ebough worldlines. [Here's a pretty good paper about it](https://ui.adsabs.harvard.edu/abs/2007AmJPh..75..434G/abstract).
Well, cutting the worldline into short sections defeats the purpose. If you're not going to evaluate over the entire trajectory, why bother formulating the stationary action concept at all?
My assessment is that that article by Taylor and Gray is ultimately only an exercise in [adding epi-cycles](https://rationalwiki.org/wiki/Adding_epicycles)
Astronomer here! If you took all the matter estimated to exist in the universe, and made it a black hole, the size of that black hole event horizon is… the size of the visible universe.
Cue “are we *in* a black hole?!” discussions over your favorite substance of choice.
There are a few un-provable, and difficult to disprove hypotheses about how the Universe could be inside of Black Hole or something. It's one of those physics things that is fun to talk about over a drink, but won't be able to have meaningful conclusions about for a long time.
Here is a [good video going over one of them.](https://www.youtube.com/watch?v=jeRgFqbBM5E)
This has always intrigued me (along with simulation theory) so I was curious to see if I could reverse-engineer the maths. Short story is: no I can't (at least I can't on my phone while eating noodles) but I was trying to figure out what seems like a paradox here.... Maybe you can help?
If the universe is expanding (and the expansion is accelerating) then I presume that means the radius is getting larger. If so, then to maintain the correlation between the universe's radius and the swartzchild radius the amount of mass must be increasing? which would break the 1st law of thermodynamics would it not?
I'm sure I'm wrong, but I can't figure out why and don't know what to Google.
Conservation of energy doesnt apply to an expanding universe as an expanding universe isnt time invariant and conservation of energy only applies to time invariant systems
I didn't know there was constraints on the laws, thanks for clarifying.
This is just conjecture but I've always imagined that it's Time that is driving universal expansion. Kinda like a time - dark energy equivalence or something.
If it's time that's 'filling' the extra space in the universe and driving expansion, then perhaps the density of the universe would remain the same despite the perceived expansion. The universal expansion would 'grow/stretch' the swartzchild radius at the same rate, so they stay in-step and thus the growth/stretching be undetectable to us. Is that right?
(not sure I explained that very well - spot the amateur)
Here's a math-lite explanation. The radius of the event horizon of a black hole (also known as the Schwarzschild radius) is proportional to its mass. That's something you can derive from general relativity.
For a fluid of constant density (which is a good approximation of the universe on cosmological scales), the mass contained within a sphere is proportional to the sphere's volume, which is proportional to its radius cubed.
Therefore, for a spherical chunk of the universe, the Schwarzschild radius of a black hole of equivalent mass grows like the cube of the radius of the sphere, so that even if the Schwarzschild radius starts off smaller than the sphere radius, it will eventually surpass it if it's large enough.
Now the really weird part is that the universe is observed to have a density that is very very close to what's known as the "critical density". For this special density, the Schwarzschild radius of all the matter within the visible universe turns out to be equal to the size of the visible universe.
Are we actually in a black hole? I don't think so. The visible universe is just that - only what is currently visible to us. As far as we know it is truly infinite in size, uniform in density, and there isn't a special "center" that would form the nucleus of the supposed cosmological black hole. If any of those things weren't true though... who knows? There is no evidence to suggest any of those things are false though.
Hey thank you for such a detailed response, I think I understood some of that. It seems like you're saying the swartzchild radius could have begun smaller than the universe and as matter increases in the universe it gets bigger faster than the universe expands and would eventually surpass the radius of the universe - is that right? So it would be a coincidence that we happen to be observing the convergence of the two radii at this point in time?
When we talk about the density of the universe, are we including dark matter and/or dark energy?
Where does the 'new' mass come from as the universe grows?
Am I just asking randomly stupid questions that make no sense? Sorry if this is the case.
2 statements are false here.
>If you took all the matter estimated to exist in the universe
Only ordinary (baryonic) matter. Ignores dark matter and dark energy contribution.
>the size of the visible universe.
the "classical" size of the visible universe. Ie a non accelerating universe.
None of which are even practical to consider these days.
I think that the cosmic microwave background radiation and the observed expansion of the universe are incompatible with the “universe is a black hole” hypothesis.
Is that true? I thought it was because a standing light wave is set up. I believe you can get a rough measurement of the speed of light by noting the frequency of light, then loading the microwave with marshmallows. Turn the microwave on and see where the marshmallows burn; you can then measure the wavelength of the light. See, e.g., https://wonders.physics.wisc.edu/measure-the-speed-of-light/
Pretty sure you guys are saying the same thing. The "standing wave" is created by the constructive/destructive interference from the wave and its reflections.
> because a standing light wave is set up
Yes, and the "cold spots" in the microwave correspond to the nodes of the standing wave. That's why your microwave has a turntable, to move the food in and out of the hot and cold spots so that it heats evenly.
In 4.5 billion years Milkway and Andromeda will merge and make an astronomical dance. The distance between stars are so big that no collisions will happen.
in space, stars are crazy far apart
Imagine our sun was shrunk to the size of a tennis ball. Then placed on the 1 yard line of a football field . Earth would be a tomato seed at the 12 yard. Neptune would be a ball bearing at the end zone on the opposite side of the field.
At this scale, how far do you go before you reach proxima centauri, the nearest star to our system?
spoiler
>! You would need to take a car out on the highway and drive for 200 kilometers. !<
I just verified and I think you made an error of an order of magnitude in your computation. If the Sun was the size of a tennis ball, Alpha Centauri would be 2000km away
My favorite cool extreme physics facts have to do with Magnetars - copying two paragraphs from here (https://solomon.as.utexas.edu/magnetar.html) below:
>**"Atoms in very strong magnetic fields**
>"The strongest magnetic field that you are ever likely to encounter personally is about 10\^4 Gauss if you have Magnetic Resonance Imaging (MRI) scan for medical diagnosis. Such fields pose no threat to your health, hardly affecting the atoms in your body. Fields in excess of 10\^9 Gauss, however, would be instantly lethal. Such fields strongly distort atoms, compressing atomic electron clouds into cigar shapes, with the long axis aligned with the field, thus rendering the chemistry of life impossible. A magnetar within 1000 kilometers would thus kill you via pure static magnetism -- if it didn't already get you with X-rays, gamma rays, high energy particles, extreme gravity, bursts and flares...
>"In fields much stronger than 10\^9 Gauss, atoms are compressed into thin needles. At 10\^14 Gauss, atomic needles have widths of about 1% of their length, hundreds of times thinner than unmagnetized atoms. Such atoms can form polymer-like molecular chains or fibers. A carpet of such magnetized fibers probably exist at the surface of a magnetar, at least in places where the surface is cool enough to form atoms."
and there's more good stuff in the source article as well!
If you don't mind me asking, how exactly would you die? Would you explode on instant, would you be stretched out like Spaghetti, would you just... Dissolve? Like you weren't even there?
Rigid crystals/solid phases of matter is a quantum effect. There's a more subtle issue, though, of microscopically non-rigid matter (like fluid phase polymers) rigidifying due to crosslinking and rigidity percolation (a statistical/non-quantum effect).
For metals, rigidity is a macroscopic result of metallic bonding holding nuclei together, then pauli pushing electrons apart.
There's a popular undergraduate calculation you can do. Assume free a rigid metal as a free electron gas in a lattice of dirac potentials (crystalline array of nuclei). The result is a bulk modulus very close to experiments.
Tl;dr you can't press solids because electrons don't like being on top of each other, and the repulsion is not electrostatic, but actually quantum mechanical in nature.
I remember a middle school teacher showing us the “bicycle wheel gyroscope” to demonstrate conservation of angular momentum, and it blew my mind. Basic stuff but still SO COOL and it definitely piqued my interest in science very early on.
That's why we try to do that demonstration so often. It's a common and popular lesson because a relatively simple concept results in something that seems impossible. Plus, us teachers feel so good when we see faces light up and become immediately fascinated in the subject.
The crazy thing is that the full explanation of the gyroscopic effect on the bicycle wheel gyroscope is much more complicated than it is often presented in lectures. From an energy point of view, the rotating wheel must fall a little immediately after letting go so that some of the potential energy is converted into rotational energy. If you want to take forces into account, it becomes even more complicated. The gyroscope experiences constraining forces due to the suspension, which prevents the gyroscope from falling. These forces can only be derived from Euler's equations of rigid body dynamics. The cause of the constraining forces is due to the fact that when the gyroscope is dropped, it rotates in a direction that is no longer parallel to a principal axis of inertia (keyword: additivity of angular velocities). This means that the justification "conservation of angular momentum" is far from sufficient. I love astonishing things whose correct explanation is even more astonishing.
Indeed the "conservation of angular momentum" narrative for gyroscopic precession is quite incorrect. Your post here is the first time I encounter someone who is aware of that (the wheel must fall a little).
About level of complexity:
The recurring pattern: many people insist on using the concept of angular momentum vector to try and understand gyroscopic precession.
But the angular momentum vector is by itself already a highly abstract concept.
My approach to understanding is: instead of using the angular momentum vector I capitalize on symmetry. I take the instantaneous plane of rotation, and I divide it in 4 quadrants, aligned with the plane of the torque.
Discussion with diagrams is available on my website:
[Gyroscope physics](http://cleonis.nl/physics/phys256/gyroscope_physics.php)
And you are also the first one here on reddit or any other forum that I encounter knowing about this issue. :D It's nice not to be alone.
I remember reading the article "It Has to Go Down A Little, In Order to Go Around" years ago you are referring on your website. Some time ago I was able to replicate the picture of Figure 1 b) with a 3d wolfram mathematica simulation using a explicit solution of Euler's equations (after correcting a few sign errors). The model showed, that the constraining forces are oscillating with time and not constant in magnitude, so that precession and decaying nutation are happening at the same time with a small, nearly vertical drop at the beginning of the motion. I never saw a good slow motion footage of a gyroscopic bicycle wheel, showing this behavior.
In videos of classroom demonstrations: invariably I observe that the demonstrator releases the gyro wheel gingerly. The demonstrator suppresses the nutation, believing it to be an irrelevant side effect.
It's quite ironic; understanding of nutation is essential, but demonstrators disregard nutation, presumably because they assume nutation is unrelated to gyroscopic precession.
Is that Wolfram Mathematica simulation saved, and publicly accessible?
Things you might not know:
Recommended article about the Dzhanibekov effect (intermediate axis theorem): Nicholas Mecholsky [Analytic formula for the Geometric Phase of an Asymmetric top](https://arxiv.org/abs/1807.03867)
Youtube video: The author explains the Dzhanibekov effect with a simulation that he implemented. Youtube channel: Physics unsimplified [Rigid body motion and the Dzhanibekov effect](https://youtu.be/NJLdW4DHRcA)
On my own website: Discussion of the rotation-of-Earth effect that is taken into account in Meteorology and Oceanography.
[Coriolis effect in Meteorology](http://cleonis.nl/physics/phys256/coriolis_in_meteorology.php)
Webpage with an animation that depicts [the essential feature of the rotation-of-Earth effect](http://cleonis.nl/physics/graphlets/coriolis_effect.php)
The rotation-of-Earth effect is a level more subtle, and a level more interesting, than is presented in the current physics textbooks.
When matter is formed from energy, it creates antimatter of equal mass. When that antimatter interacts with matter, it destroys each other in a process called "annihilation".
However, there is a *very very very very small chance* that more matter is formed than antimatter. And during the Big Bang, because the process happens a gazillion times per second, the entire mass of the universe was blipped into existence in an instant.
And we don't know why.
Ugh, yeah if we could get an explanation for this apparent imbalance (asymmetry?), it seems like it would help with the nagging “why is there something rather than nothing” question.
Humans are largely made up of stars. More specifically, the heavier elements that fuse from immense heat and pressure inside it and are released upon the stars death are inside of us. The life cycle of countless stars had to take place to make life.
Straying only slightly from physics, on a philosophical level you could view this as the universe creating us to experience itself
You're right, but I think for the wrong reason. We're mostly water, which is hydrogen and oxygen. The hydrogen was made in the Big Bang, but the oxygen was made in the centers of stars during their usual fusion lifetime (not during supernovae). By mass, we're definitely mostly oxygen.
Definitely anything beyond ~~lead~~ iron in us is from supernovae, the death of stars.
I carefully didn’t mention supernova assuming stating that stars fuse heavier elements and release them when they die would technically include both ordinary stars’ usual fusion lifetime (and ultimate star death > expelled gas) *and* supernova, correct me if I’m wrong
Anything beyond Iron is from supernova, not lead. Things beyond iron come partially from supernova, but for a lot of those elements I think the majority comes from merging neutron stars.
>We are stardust
>Billion year old carbon
>We are golden
>Caught in the devil's bargain
>And we've got to get ourselves
>Back to the garden
-Joni Mitchell
The concept of seeing things from the past doesn't really make sense. What is the past if you can't even see it in the present?
I'm not stating facts here, just giving my opinion and trying to open a discussion
For me the weirdest part was the implication that simultaneity is relative. Not only time goes faster or slower according to circumstances, but the order in which distant events occur can also change. It can be A then B for us but B then A for another reference frame.
It means to measure light accurately, or at all, you need to reflect it and measure it on the return path (so two way). This is because if you measure one way, the measuring device can never accurately know which time the light started at in its own reference frame. But if you measure two way, start and end is in the same reference frame and the time difference can be clearly obtained.
This type of thing makes me feel like someone with dissociative identity disorder… a large part of me is perfectly willing to accept this and even run thought experiments based on this principle. But the carpenter in me thinks we’re just measuring weird. And it’s simultaneous.
But C is universal no? It must be the same in any direction and every direction even if we change our frame of reference for that matter . Where am I wrong ?
1. Photons don't experience time because they travel at the speed of light. That means for a photon emitted by the big bang that travels through space for a trillion trillion years (by our measure) until the heat death of he universe... That whole adventure was one instant
2. Space is expanding faster than the speed of light so in the future there will be isolated galaxy clusters (or even lone galaxies) that can't see the wider universe at all, and never will. Intelligent civilisations evolving there will think that's the entire universe, not knowing there are trillions more clusters like theirs out there.
3. The "shape"of the known universe (how the matter is arranged) is a leftover imprint of the quantum fluctuations that were occurring in a very small space at the time of the big bang. Like a drawing on a balloon once it's blown up.
When satellites perform gravity assist manoeuvres around planets, they are essentially stealing a tiny bit of energy from that planet, causing it to rotate a bit slower than before. The effect is infinitesimally small, but very real.
Awe for me goes to Noether’s theorem, which states for every continuous symmetry of the action of a physical system has an associated conservation law. For example, broadly speaking, if the action is time-independent, energy is conserved. Conservation laws give rise to physical laws, like Newton’s laws of motion, so essentially the universe is the way it is because of symmetries.
Maxwell’s demon and Landauer's principle suggests that entropy is not disorder but rather information. and that information, in the sense of computer bits, 1s and 0s are physical thermodynamic quantities related to entropy and thus heat, temperature and energy. the connection between thermodynamics, statistical physics, and informational theory is long and fascinating. this is a bridge between physics and many other branches of science and engineering. for example, the fisher information in statistics is related to generalized temperature in statistical mechanics.
I have done some work in information theory, and I felt maybe I should say something about this pervasive notion that entropy is disorder. At a very technical level, the entropy of a system is the average number of bits you need to describe the state of the system. This is not an intuition gathered from stat mech, but what we call the 'operational interpretation' of the Shannon entropy. You can look up Shannon's noiseless coding theorem for a reference.
The link to 'disorder' is more subtle. What does disorder mean? Well again in a very technical sense you might say that a system is more disordered if you have very little certainty if you try to guess its state. As it turns out, the uniform distribution maximises this uncertainty (or minimises the success probability of guessing). For a source regarding the above check 'min entropy'.
As it so happens, the entropy itself increases as the distribution of a system comes 'near' the uniform distribution (in some suitable sense of 'near', see 1-norm between probability distributions).
Now regarding your second statement that Landauer said entropy is information, actually what he argued is as follows: One needs to do work to set or reset the value of a bit. What you wrote is extremely confusing sonce you did not make clear the entropy of which system you are referring to. What I think you meant was that the 'bit' is a state of some system and one needs to do work to change the state of that system.
And here you have a contradiction since this statement is decidedly untrue. One does not need to do any work to change the state of a quantum system, since one ks only allowed Unitary operations. This very much also extends to classical computation as well ( See Reversible Computation via Tofoli gates).
So the actual correct (and accepted) interpretation of Landauer's statement is this: Any irreversible computation changes the entropy of a system. Since one needs to do work for irreversible computations that implies work changes the entropy of a system. This is provable (very easily) within the framework of quantum mechanics but none the less is cool.
Every force has an infinite reach, though its strength diminishes quickly when you move away from the origin. That being said the magnets in your phone experience magnetic force due to a random magnetic field created from a random star in a random galaxy. So it's not only gravity.
If a sustained A note is playing in a soundproof room, and someone in the next room over opens the door so they can hear, but only for a very short time (~1 ms), the sound the person hears isn’t an A note, but rather, a combination of frequencies that doesn’t correspond to any one note.
Oobleck rigidifies because shear stress causes the suspended starch particles to form a network of frictional contacts, whose rigidity* causes a transition from a fluid to a solid.
*in the sense of Maxwell constraint counting
Ok this one stopped me scrolling, can you tell me if I’m unpacking the poetic language fairly?
I think by “math” you mean something like “our symbolic representation of relationships between quantities.” And by “explain” the universe you probably mean “describe” the universe, which avoids the issues around human comprehension. Is that about right?
The boring implication here is that all our ignorance is due to (1) we haven’t discovered some relevant features, (2) we haven’t discovered some relevant math, and (3) we don’t find our mathematical descriptions to be satisfactory explanations (see prior paragraph). This doesn’t seem too controversial, but it doesn’t imply that we’re capable of overcoming these deficits (even if we don’t destroy ourselves before we have the opportunity).
The more exciting implication is that math has some kind of universality, that no feature is beyond the ability for math to describe, that measurable quantities and relationships between them can be fully symbolized and systematized, yielding an all-powerful abstract model. I’m no philosopher so it doesn’t feel like I’m doing this justice.
The absolutely mind-blowing implication is that math can describe possibilities that our particular universe doesn’t instantiate — maybe *all* the possibilities?! That math is powerful enough to describe more than just the possible relationships of our particular universe?! So if different constants or starting conditions are possible, math would still describe everything?!
Just… yikes!
The fact that everything in theoretical physics points towards the idea that everything in the universe is a single object, inseparable of everything else. On the standard model there are like 19 objects, but almost every theory that has the potential of replacing the standard model reduces the number of objects of the theory.
Antimatter - and the sequence of events leading up to it:
In a 1926 letter to Paul Ehrenfest, Albert Einstein wrote, "I am toiling over Dirac. This balancing on the dizzying path between genius and madness is awful".
In 1928, Paul Dirac postulated the existence of positively charged electrons and in general anti-particles for every particle. The result was an equation describing both matter and antimatter in terms of quantum fields.
1932 Carl Anderson at Cal Tech discovers the positron in a cloud chamber
FWIW I do think the whole matter/antimatter annihilation thing is very cool. As is the synthesis of Positronium, if only it had a longer half life. :)
A ping pong ball can stand up to over 3000Gs of acceleration (0-450m/s down a 3m barrel ~= 33750m/s^2): https://i.imgur.com/lHNb8lC.mp4
You can build a jumbo model of a Paul Ion Trap (to trap charged dust) using a neon sign transformer: https://i.imgur.com/EJgg91N.mp4
Hook a wire coil to a milliamp meter, push a magnet in the coil and watch the meter give a reading. You are actually pushing subatomic particles (electrons) around. Think about that for a moment.
There aren’t enough different smell receptors in the nose corresponding to the number of smells that humans can identify. My lecturer was saying that the smell particle and the receptors may entangle with one another, transferring the information to the brain about the smell it’s detected?? Something like that. Was pretty cool it blew all our minds haha
Having never thought about it until 5 seconds ago, I'm guessing it's similar to looking at the light receptors in an eye and wondering if humans can see more than three colours
Yes, this is fairly close to the actual mechanism. The nose can detect a cubic bunch-ton of aromatic molecules but between nose and brain is an extra layer of cells (glomerulii) that act like an 'enhance video' trick and feed that 'smell image' to (various parts of) our brain for processing.
There was a very readable book detailing one wacky theory about how the sense of smell works, [The Emperor of Scent](https://www.goodreads.com/en/book/show/14546). Pretty sure it's largely inaccurate but was an interesting theory.
That gravity might not be a fundamental force, like electromagnetism, but instead an entropic effect, like a rubber band coming back to the smallest shape.
Everything travels at the speed of light. It's just that, if you have mass, most of that movement is through time.
Floatheadphysics has [a great video](https://www.youtube.com/watch?v=TJmgKdc7H34) on this.
THE BARKHAUSEN EFFECT: Hearing magnetic domains move!
Copying an excerpt from Martin Gardner's book The New Ambidextrous Universe, Chapter 19
"The atoms in an unmagnetized bar of iron are not oriented in individually random ways. They tend to form little clumps or sets called domains in which the magnetic axes of the atoms are parallel. It is these domains, not the individual atoms, that have their magnetic axes turned in different directions. When the bar is magnetized by placing it in a strong outside field, the walls of these little domains shift as their atoms turn to align their axes with the axis of the outside field.
The domains in the bar do not all swing into line simultaneously. As a result, the bar's magnetic field grows stronger in a series of abrupt little jumps. If a wire is wrapped around a bar that is being magnetized, each jump induces a small voltage in the wire. These electrical impulses can be amplified and actually heard as a series of clicks, a sort of rustling sound like that of paper being crumpled. This is called the Barkhausen effect, after Heinrich Barkhausen, a German engineer who discovered it
in 1919. If you should visit the fabulous Museum of Science and Industry in Chicago, you can push a button and actually hear the Barkhausen effect. As you watch a small bar of iron move slowly into a magnetic field, you will hear the amplified rustling noise that results from the discontinuous movement of domain walls as the bar's atoms swing into alignment."
Nothing can escape the gravity of black hole, but it can emit Hawkins radiation proving that light can be a particle and a wave in different circumstances.
Bernoulli’s principle — essentially says that pressure plus velocity must remain constant. Velocity increases, pressure decreases to compensate; pressure increases, velocity decreases to compensate. It’s why planes fly and why people get pulled infront of trains if they stand too close.
Bernoulli's principle only applies to streamlines, so it doesn't really explain why airplanes fly.
Watch this from 15:05-19:49 for a short, more nuanced look as to problems with using Bernoulli's law to try and explain lift:
https://youtu.be/QKCK4lJLQHU?si=5GrHXee_fDzQOTT-
Infinity makes me uncomfortable ( or trying to imagine it too much), so the fact there is a physical limit of the observable universe is both beautiful, sad and comforting to me.
[there are no particles. only fields.](https://pubs.aip.org/aapt/ajp/article-abstract/81/3/211/1032373/There-are-no-particles-there-are-only-fields?redirectedFrom=fulltext)
Wave particle duality is the current understanding of physics, with waves and fields just being different words for the same thing.
There’s quantum interpretations with only fields (https://en.m.wikipedia.org/wiki/De_Broglie–Bohm_theory) and interpretations with only particles where the waves are just statistically emergent behaviour (https://en.m.wikipedia.org/wiki/Ensemble_interpretation), but none of the interpretations have been proven correct
Hong-Ou-Mandel intereference is a two-photon intereference effect. If you send two indistinguishable photons at a beam-splitter, they exit together instead of taking separate paths. See also [Wiki article](https://en.wikipedia.org/wiki/Hong%E2%80%93Ou%E2%80%93Mandel_effect) and [video](https://www.youtube.com/watch?v=BFIM5pHyd1k).
Magnets aren't about metals, or even attraction and repulsion
but really its about how moving charges affect other moving charges
A permanent magnet on a constant, uniform magnetic field, while being aligned with magnetic field direction, won't feel a thing
Coolest(literally) physics fact:
coldest temp achieved in lab is 38 picokelvins, 38trillionth of a degree above absolutely zero. They had used a quantum gas lens and drop tower to create a BEC (Bose Einstein Condensate). It lasted for about 2 seconds.
Because of special relativity it is 100% possible to time travel into the future. There is nothing other than technology preventing us from doing it. Travelling into the past is a whole nother bucket of worms and may or, more likely, may not be possible.
Since the universe seems to be expanding, light emitted from stars that’s traveling to us has its wavelength changed over time. This is called Red Shift. The space that the light is traveling through is literally stretching the wave/particle as it expands
Not sure if this is necessarily physics related, but all music is math fundamentally and it makes me wonder about "good music" and it's relation to the numbers that orchestrate it.
Due to the influence of gravity over 4 and a half billion years, the core of the earth is two and a half years younger than the crust.
Even though I know the relativistic effects of gravity differences, it never occurred to me that the earths core would, in fact be younger because of this. Gosh, darn it do I love Physics!
Since the core is very hot, all the particles within the core are moving much faster. Would this contribute to the age difference due to special relativity considerations?
It's a solid core.
But it’s very hot.
But because it is solid, the age dilation from the gravitational field will be far greater than any "savings" via special relativity. It would need to be moving fast enough to break its structure in order to dominate the equation.
Time dilation due to movement does not require a particle to be moving in one direction. Hotter particles are absolutely moving faster, even if that's just the brownian motion of heat within a solid structure. I think his idea has merit. This would make the core younger past the 2.5 years.
I did consider it, and I gave a quick judgment response as we are comparing 5000C to 3500C - 1000C depending on where we're measuring. It isn't enough of a delta to compensate for the time dilating effects of gravity.
Fair enough. I misunderstood the point from the beginning but you made it clear, thanks.
Wow, via what mechanism?
time dilation in a gravitational field
Could something similar be said for any sufficiently large object? For instance, could the atoms in an apple core be zeptoseconds younger than its skin?
Given all mass produces* a gravitational field, I don’t see why not, but you’re probably quite a few orders of magnitude off. \*not sure *exactly* what the relationship is
This is really cool.
Does time dilation depend on potential/force, or something else? If you're a particle in the core, the only (newtonian) gravitational force you experience is due the mass that's beneath you as the larger sphere does not influence you. As such, the acceleration due to gravity would be much lower there I presume. But if that is not how it works, and all of the mass contributes, then the time dilation should be undefined (tending to infinity as you go closer to the core) exactly at the core, right?
Not infinity at the core, no. That’s black hole stuff.
Hang in, in Newtonian gravity any thing at the centre of a mass would experience no gravity. I imagine the same would be true in general relativity. So wouldn’t that mean there’s no time dilation at the core, but it’s the mantle which is younger?
It's not that it doesn't experience gravity, it experiences no NET FORCE of gravity. It is still under higher gravity, but from all sides.
The Leidenfrost effect allows a person to plunge their fingers into molten lead* and remove them unscathed. A thin layer of water essentially forms a protective barrier on the surface of the fingers. *Under very specific circumstances, do not try at home
Instructions unclear, I now have a solder plated dong
Unfortunate schmelting accident.
I love goooooooold
You fuckers are why I'm here
Instructions unclear, I now have no dong
It disappeared, without a *trace*
This also works with molten iron and rock, if the viscosity is low enough. If the viscosity is not low enough then you get a much more exciting, if less entertaining result.
This reads exactly like *due to its material properties and shape, it's actually impossible to break an egg by squeezing it in one hand.*
Not impossible, really hard. I'm sure if you spend half a career exercising your hand muscles you can crack an egg horizontally.
And you can use the same effect to safely "hold" liquid nitrogen in the palm of your hand. \* Again, there are important caveats. Do not try at home!
Also works with liquid nitrogen - I have plunged my hand into liquid nitrogen (and took it out quickly!) as well as put some on my tongue for a cool (no pun intended) effect.
I did this with LN2. It totally works!
Stars have negative heat capacity. If you'd put them into a giant oven, they would actually cool down (however they would expand, thus storing the additional energy emitted from the oven in the form of potential energy)
>Stars have negative heat capacity. That is cool.
*i\_see\_what\_you\_did\_there.gif*
Took me wayyyyy too long to get it lol
lol me too
Gravitationally bound systems also have negative heat capacity
Also, last I checked, hypergiant stars have density less than our atmosphere. Not sure if smaller stars do as well but I think the hotter they get the more they puff out. Also for black holes, their mass is proportional to their schwarzchild radius, so if you say they have a density defined by the volume in their event horizon, they get far less dense as they get more massive. Although that may be an absurd metric and who knows if that equation for radius really is accurate.
Isn't this only for white dwarfs? I hear they maintain their shape due to Fermi Degeneracy pressure only. Do regular stars also have states filled all the way up?
I know this is true for black holes, how do you determine this for stars? Does it depend on the type of star?
Uh, it was an exercise for an astrophysics exam in my undergrad a couple years ago. If I remember correctly, it was an application of the virial theorem (https://en.wikipedia.org/wiki/Virial_theorem?wprov=sfla1) on a gravitational bound gas cloud, but don't quote me on that, it is not my area of expertise any more. Most importantly I remember the result, we discussed it broadly in our exercise class and it blew everyone's mind, even the tutor got excited about it!
Skimming over the Wikipedia article I shared, this is exactly the case for cores of stars, even off the main sequence. I remember having vivid thought experiments for a couple of weeks just to wrap my mind around this! Such a fascinating topic in physics.
Thanks I’ll have to try it out, I know for blackholes it’s super easy once you have the entropy. My first thought was “stars are just balls of gas, why would they behave differently”, but now I’m thinking it’s probably due to gravity. Wonder if I could just add a gravitational term to the Hamilton, construct the partition function and determine entropy…
Funny enough, I remember the exact same thing from my undergrad astrophysics.
If viewed through sufficient length (one or two meters at least), water appears blue, not clear. This is mostly because the energy associated with vibrational frequency transitions of water molecules absorbs light in the red end of the visible EM spectrum more than the violet end. Heavy water (deuterium oxide), however, is clear, because the absorption spectrum is shifted into the infrared due to its heavier hydrogen atoms. Also, I don't know if this has been tested before, but in theory, because spectral bands undergo broadening at higher temperatures and one of the absorption bands of water is just barely outside the visible part of the spectrum in the infrared unless it is broadened sufficiently, hot water should be more blue than cold or room temperature water.
When SCUBA diving, you can see all the colors fall off as you go deeper. Red goes away in only a few feet, it seems like. Down deep, 30+ meters, everything is almost greyscale in blue - that is, until you bring out a dive light.
[Hot water should indeed be bluer](https://www.researchgate.net/figure/Pure-water-absorption-spectra-measured-as-a-function-of-temperature-15-65-C-The_fig3_44676498)
Not saying you're wrong, but how can you conclude that since the plot is not in the visible spectrum?
The key part is actually the 650-750 nm region which is safely visible but a bit hard to see on the original plot, which is also weakly [increasing with temperature](https://imgur.com/a/RsoCBLJ) (This paper uses the arrow to point in direction of decreasing temperature for some reason). This region is also the most [significant visible absorption](https://www.researchgate.net/figure/Absorption-coefficient-of-visible-light-in-water-2_fig1_316232236) for water. That's all I was going on before but [this paper](https://opg.optica.org/ao/viewmedia.cfm?uri=ao-36-24-6035&seq=0) also reports no significant temperature dependent absorption for water outside this band and its next overtone in the visible (unfortunately no pretty plots).
My favorite is the principle of least action. All of newtons laws can be developed from one principle: that the path an object takes through space will be the one such that the transfer from potential to kinetic energy along its path will be a minimum. Its hugely important in quantum mechanics and is mostly not mentioned in undergraduate physics.
It’s actually the principle of stationary action as sometimes the solution is a maximum or an inflection point (the most common examples are in optics when looking at the path of light in strange circumstances - like concave mirrors or materials with negative refractive indexes). It’s unhelpful things like that which make it less popular to reach to undergrads unless they’re specialising in an area like particle physics where Lagrangians turn up a lot
You could also say that it's the principle of locally minimized action, where the action is minimized over short ebough worldlines. [Here's a pretty good paper about it](https://ui.adsabs.harvard.edu/abs/2007AmJPh..75..434G/abstract).
Well, cutting the worldline into short sections defeats the purpose. If you're not going to evaluate over the entire trajectory, why bother formulating the stationary action concept at all? My assessment is that that article by Taylor and Gray is ultimately only an exercise in [adding epi-cycles](https://rationalwiki.org/wiki/Adding_epicycles)
My uni taught Lagrangian mechanics in the 2nd year of undergrad. I think nowadays they mostly cover it early on.
I didn't know about it's connection to the schrodinger equation till much later.
In the core of the Sun, the actual continuous power output is only about 200 watts per cubic meter, which is roughly the heat put out by two candles.
Is that because it's the core, or is it because the sun output is due to all of its cubic meters?
The latter. Individual bits of sun don't produce that much heat, but there's so much of it that the total heat output is enormous.
Going off this one, humans have a higher output/volume. A ball of humans the size of the sun would in fact be way hotter! I did the math once.
Astronomer here! If you took all the matter estimated to exist in the universe, and made it a black hole, the size of that black hole event horizon is… the size of the visible universe. Cue “are we *in* a black hole?!” discussions over your favorite substance of choice.
Woah, how have I never heard this? Surely there are some fun theories behind it
There are a few un-provable, and difficult to disprove hypotheses about how the Universe could be inside of Black Hole or something. It's one of those physics things that is fun to talk about over a drink, but won't be able to have meaningful conclusions about for a long time. Here is a [good video going over one of them.](https://www.youtube.com/watch?v=jeRgFqbBM5E)
This has always intrigued me (along with simulation theory) so I was curious to see if I could reverse-engineer the maths. Short story is: no I can't (at least I can't on my phone while eating noodles) but I was trying to figure out what seems like a paradox here.... Maybe you can help? If the universe is expanding (and the expansion is accelerating) then I presume that means the radius is getting larger. If so, then to maintain the correlation between the universe's radius and the swartzchild radius the amount of mass must be increasing? which would break the 1st law of thermodynamics would it not? I'm sure I'm wrong, but I can't figure out why and don't know what to Google.
Conservation of energy doesnt apply to an expanding universe as an expanding universe isnt time invariant and conservation of energy only applies to time invariant systems
I didn't know there was constraints on the laws, thanks for clarifying. This is just conjecture but I've always imagined that it's Time that is driving universal expansion. Kinda like a time - dark energy equivalence or something. If it's time that's 'filling' the extra space in the universe and driving expansion, then perhaps the density of the universe would remain the same despite the perceived expansion. The universal expansion would 'grow/stretch' the swartzchild radius at the same rate, so they stay in-step and thus the growth/stretching be undetectable to us. Is that right? (not sure I explained that very well - spot the amateur)
Here's a math-lite explanation. The radius of the event horizon of a black hole (also known as the Schwarzschild radius) is proportional to its mass. That's something you can derive from general relativity. For a fluid of constant density (which is a good approximation of the universe on cosmological scales), the mass contained within a sphere is proportional to the sphere's volume, which is proportional to its radius cubed. Therefore, for a spherical chunk of the universe, the Schwarzschild radius of a black hole of equivalent mass grows like the cube of the radius of the sphere, so that even if the Schwarzschild radius starts off smaller than the sphere radius, it will eventually surpass it if it's large enough. Now the really weird part is that the universe is observed to have a density that is very very close to what's known as the "critical density". For this special density, the Schwarzschild radius of all the matter within the visible universe turns out to be equal to the size of the visible universe. Are we actually in a black hole? I don't think so. The visible universe is just that - only what is currently visible to us. As far as we know it is truly infinite in size, uniform in density, and there isn't a special "center" that would form the nucleus of the supposed cosmological black hole. If any of those things weren't true though... who knows? There is no evidence to suggest any of those things are false though.
Hey thank you for such a detailed response, I think I understood some of that. It seems like you're saying the swartzchild radius could have begun smaller than the universe and as matter increases in the universe it gets bigger faster than the universe expands and would eventually surpass the radius of the universe - is that right? So it would be a coincidence that we happen to be observing the convergence of the two radii at this point in time? When we talk about the density of the universe, are we including dark matter and/or dark energy? Where does the 'new' mass come from as the universe grows? Am I just asking randomly stupid questions that make no sense? Sorry if this is the case.
2 statements are false here. >If you took all the matter estimated to exist in the universe Only ordinary (baryonic) matter. Ignores dark matter and dark energy contribution. >the size of the visible universe. the "classical" size of the visible universe. Ie a non accelerating universe. None of which are even practical to consider these days.
I think that the cosmic microwave background radiation and the observed expansion of the universe are incompatible with the “universe is a black hole” hypothesis.
Fascinating! Does this include or exclude dark matter theories?
Cold spots in the microwave is a result of the microwaves destructively interfering and thus canceling out
Is that true? I thought it was because a standing light wave is set up. I believe you can get a rough measurement of the speed of light by noting the frequency of light, then loading the microwave with marshmallows. Turn the microwave on and see where the marshmallows burn; you can then measure the wavelength of the light. See, e.g., https://wonders.physics.wisc.edu/measure-the-speed-of-light/
Pretty sure you guys are saying the same thing. The "standing wave" is created by the constructive/destructive interference from the wave and its reflections.
> because a standing light wave is set up Yes, and the "cold spots" in the microwave correspond to the nodes of the standing wave. That's why your microwave has a turntable, to move the food in and out of the hot and cold spots so that it heats evenly.
[удалено]
Standing wave defeats standing dish, news at 11
In 4.5 billion years Milkway and Andromeda will merge and make an astronomical dance. The distance between stars are so big that no collisions will happen.
in space, stars are crazy far apart Imagine our sun was shrunk to the size of a tennis ball. Then placed on the 1 yard line of a football field . Earth would be a tomato seed at the 12 yard. Neptune would be a ball bearing at the end zone on the opposite side of the field. At this scale, how far do you go before you reach proxima centauri, the nearest star to our system? spoiler >! You would need to take a car out on the highway and drive for 200 kilometers. !<
I just verified and I think you made an error of an order of magnitude in your computation. If the Sun was the size of a tennis ball, Alpha Centauri would be 2000km away
I believe the original version had sun as a grape. Earth is a "penciled dot on a paper".
My favorite cool extreme physics facts have to do with Magnetars - copying two paragraphs from here (https://solomon.as.utexas.edu/magnetar.html) below: >**"Atoms in very strong magnetic fields** >"The strongest magnetic field that you are ever likely to encounter personally is about 10\^4 Gauss if you have Magnetic Resonance Imaging (MRI) scan for medical diagnosis. Such fields pose no threat to your health, hardly affecting the atoms in your body. Fields in excess of 10\^9 Gauss, however, would be instantly lethal. Such fields strongly distort atoms, compressing atomic electron clouds into cigar shapes, with the long axis aligned with the field, thus rendering the chemistry of life impossible. A magnetar within 1000 kilometers would thus kill you via pure static magnetism -- if it didn't already get you with X-rays, gamma rays, high energy particles, extreme gravity, bursts and flares... >"In fields much stronger than 10\^9 Gauss, atoms are compressed into thin needles. At 10\^14 Gauss, atomic needles have widths of about 1% of their length, hundreds of times thinner than unmagnetized atoms. Such atoms can form polymer-like molecular chains or fibers. A carpet of such magnetized fibers probably exist at the surface of a magnetar, at least in places where the surface is cool enough to form atoms." and there's more good stuff in the source article as well!
If you don't mind me asking, how exactly would you die? Would you explode on instant, would you be stretched out like Spaghetti, would you just... Dissolve? Like you weren't even there?
If it’s rapid, I would say vaporise probably, if it’s gradual, melt and then vaporise.
Rigid matter is a quantum effect.
Rigid crystals/solid phases of matter is a quantum effect. There's a more subtle issue, though, of microscopically non-rigid matter (like fluid phase polymers) rigidifying due to crosslinking and rigidity percolation (a statistical/non-quantum effect).
How so?
For metals, rigidity is a macroscopic result of metallic bonding holding nuclei together, then pauli pushing electrons apart. There's a popular undergraduate calculation you can do. Assume free a rigid metal as a free electron gas in a lattice of dirac potentials (crystalline array of nuclei). The result is a bulk modulus very close to experiments. Tl;dr you can't press solids because electrons don't like being on top of each other, and the repulsion is not electrostatic, but actually quantum mechanical in nature.
Pauli exclusion?
and chemical bonds.
I remember a middle school teacher showing us the “bicycle wheel gyroscope” to demonstrate conservation of angular momentum, and it blew my mind. Basic stuff but still SO COOL and it definitely piqued my interest in science very early on.
That's why we try to do that demonstration so often. It's a common and popular lesson because a relatively simple concept results in something that seems impossible. Plus, us teachers feel so good when we see faces light up and become immediately fascinated in the subject.
The crazy thing is that the full explanation of the gyroscopic effect on the bicycle wheel gyroscope is much more complicated than it is often presented in lectures. From an energy point of view, the rotating wheel must fall a little immediately after letting go so that some of the potential energy is converted into rotational energy. If you want to take forces into account, it becomes even more complicated. The gyroscope experiences constraining forces due to the suspension, which prevents the gyroscope from falling. These forces can only be derived from Euler's equations of rigid body dynamics. The cause of the constraining forces is due to the fact that when the gyroscope is dropped, it rotates in a direction that is no longer parallel to a principal axis of inertia (keyword: additivity of angular velocities). This means that the justification "conservation of angular momentum" is far from sufficient. I love astonishing things whose correct explanation is even more astonishing.
Indeed the "conservation of angular momentum" narrative for gyroscopic precession is quite incorrect. Your post here is the first time I encounter someone who is aware of that (the wheel must fall a little). About level of complexity: The recurring pattern: many people insist on using the concept of angular momentum vector to try and understand gyroscopic precession. But the angular momentum vector is by itself already a highly abstract concept. My approach to understanding is: instead of using the angular momentum vector I capitalize on symmetry. I take the instantaneous plane of rotation, and I divide it in 4 quadrants, aligned with the plane of the torque. Discussion with diagrams is available on my website: [Gyroscope physics](http://cleonis.nl/physics/phys256/gyroscope_physics.php)
And you are also the first one here on reddit or any other forum that I encounter knowing about this issue. :D It's nice not to be alone. I remember reading the article "It Has to Go Down A Little, In Order to Go Around" years ago you are referring on your website. Some time ago I was able to replicate the picture of Figure 1 b) with a 3d wolfram mathematica simulation using a explicit solution of Euler's equations (after correcting a few sign errors). The model showed, that the constraining forces are oscillating with time and not constant in magnitude, so that precession and decaying nutation are happening at the same time with a small, nearly vertical drop at the beginning of the motion. I never saw a good slow motion footage of a gyroscopic bicycle wheel, showing this behavior.
In videos of classroom demonstrations: invariably I observe that the demonstrator releases the gyro wheel gingerly. The demonstrator suppresses the nutation, believing it to be an irrelevant side effect. It's quite ironic; understanding of nutation is essential, but demonstrators disregard nutation, presumably because they assume nutation is unrelated to gyroscopic precession. Is that Wolfram Mathematica simulation saved, and publicly accessible? Things you might not know: Recommended article about the Dzhanibekov effect (intermediate axis theorem): Nicholas Mecholsky [Analytic formula for the Geometric Phase of an Asymmetric top](https://arxiv.org/abs/1807.03867) Youtube video: The author explains the Dzhanibekov effect with a simulation that he implemented. Youtube channel: Physics unsimplified [Rigid body motion and the Dzhanibekov effect](https://youtu.be/NJLdW4DHRcA) On my own website: Discussion of the rotation-of-Earth effect that is taken into account in Meteorology and Oceanography. [Coriolis effect in Meteorology](http://cleonis.nl/physics/phys256/coriolis_in_meteorology.php) Webpage with an animation that depicts [the essential feature of the rotation-of-Earth effect](http://cleonis.nl/physics/graphlets/coriolis_effect.php) The rotation-of-Earth effect is a level more subtle, and a level more interesting, than is presented in the current physics textbooks.
When matter is formed from energy, it creates antimatter of equal mass. When that antimatter interacts with matter, it destroys each other in a process called "annihilation". However, there is a *very very very very small chance* that more matter is formed than antimatter. And during the Big Bang, because the process happens a gazillion times per second, the entire mass of the universe was blipped into existence in an instant. And we don't know why.
Ugh, yeah if we could get an explanation for this apparent imbalance (asymmetry?), it seems like it would help with the nagging “why is there something rather than nothing” question.
Answer lies in higher dimensions
*deep toke* I'm ready!
Humans are largely made up of stars. More specifically, the heavier elements that fuse from immense heat and pressure inside it and are released upon the stars death are inside of us. The life cycle of countless stars had to take place to make life. Straying only slightly from physics, on a philosophical level you could view this as the universe creating us to experience itself
You're right, but I think for the wrong reason. We're mostly water, which is hydrogen and oxygen. The hydrogen was made in the Big Bang, but the oxygen was made in the centers of stars during their usual fusion lifetime (not during supernovae). By mass, we're definitely mostly oxygen. Definitely anything beyond ~~lead~~ iron in us is from supernovae, the death of stars.
I carefully didn’t mention supernova assuming stating that stars fuse heavier elements and release them when they die would technically include both ordinary stars’ usual fusion lifetime (and ultimate star death > expelled gas) *and* supernova, correct me if I’m wrong
Anything beyond Iron is from supernova, not lead. Things beyond iron come partially from supernova, but for a lot of those elements I think the majority comes from merging neutron stars.
There was no hydrogen in the big bang. Nor were there even protons for a little bit
Hydrogens formed in nuecleogenesis, it took place 3 minutes after big bang
3 minutes of earth time or 3 minutes next to the big bang (considerably more earth minutes)?
That's a longggg time after the big bang.
>We are stardust >Billion year old carbon >We are golden >Caught in the devil's bargain >And we've got to get ourselves >Back to the garden -Joni Mitchell
Everything that you can see, you are seeing from the past because of the finite speed of light.
And even more limited brain processing speed.
Yes, or as Sagan put it "Telescopes are time machines".
The concept of seeing things from the past doesn't really make sense. What is the past if you can't even see it in the present? I'm not stating facts here, just giving my opinion and trying to open a discussion
Time is relative
Don’t see how this isn’t the go to answer. Whatever other whacky stuff there is you can’t really beat relativity of simultaneity.
It's even more of a head trip when you realize time can be viewed as the 4th spatial dimension.
Yeah it's all deeply, deeply weird And that's before you even start to consider qm
And its even more weird if you consider that everything moves at c through 4 dimensional space time
For me the weirdest part was the implication that simultaneity is relative. Not only time goes faster or slower according to circumstances, but the order in which distant events occur can also change. It can be A then B for us but B then A for another reference frame.
If you drive at a red light fast enough it turns green. (There are a few caveats)
and there would still be a lifted chevy silverado tailgating you
The coolest fact? There is no non-rest energy in a substance at 0 Kelvin.
Lol, I see what you did there 😏
We cannot measure the speed of light in One Direction since relativity effects our ability to have synchronized timing devices
What does One Direction mean here?
It means to measure light accurately, or at all, you need to reflect it and measure it on the return path (so two way). This is because if you measure one way, the measuring device can never accurately know which time the light started at in its own reference frame. But if you measure two way, start and end is in the same reference frame and the time difference can be clearly obtained.
This type of thing makes me feel like someone with dissociative identity disorder… a large part of me is perfectly willing to accept this and even run thought experiments based on this principle. But the carpenter in me thinks we’re just measuring weird. And it’s simultaneous.
You’ll find this interesting: https://youtu.be/pTn6Ewhb27k
Knew what it’d be before clicking, lol. Love that video
They’re this British boy band that formed in 2010
Ha ha I was expecting this comment : )
But C is universal no? It must be the same in any direction and every direction even if we change our frame of reference for that matter . Where am I wrong ?
The video posted above explains it all in detail https://youtu.be/pTn6Ewhb27k?si=tIRr6vKAIYiYYLF7
Apart from gravity almost all day to day interactions you see are of electromagnetic nature
1. Photons don't experience time because they travel at the speed of light. That means for a photon emitted by the big bang that travels through space for a trillion trillion years (by our measure) until the heat death of he universe... That whole adventure was one instant 2. Space is expanding faster than the speed of light so in the future there will be isolated galaxy clusters (or even lone galaxies) that can't see the wider universe at all, and never will. Intelligent civilisations evolving there will think that's the entire universe, not knowing there are trillions more clusters like theirs out there. 3. The "shape"of the known universe (how the matter is arranged) is a leftover imprint of the quantum fluctuations that were occurring in a very small space at the time of the big bang. Like a drawing on a balloon once it's blown up.
Yeah those first two are doozies.
When satellites perform gravity assist manoeuvres around planets, they are essentially stealing a tiny bit of energy from that planet, causing it to rotate a bit slower than before. The effect is infinitesimally small, but very real.
Awe for me goes to Noether’s theorem, which states for every continuous symmetry of the action of a physical system has an associated conservation law. For example, broadly speaking, if the action is time-independent, energy is conserved. Conservation laws give rise to physical laws, like Newton’s laws of motion, so essentially the universe is the way it is because of symmetries.
Maxwell’s demon and Landauer's principle suggests that entropy is not disorder but rather information. and that information, in the sense of computer bits, 1s and 0s are physical thermodynamic quantities related to entropy and thus heat, temperature and energy. the connection between thermodynamics, statistical physics, and informational theory is long and fascinating. this is a bridge between physics and many other branches of science and engineering. for example, the fisher information in statistics is related to generalized temperature in statistical mechanics.
I have done some work in information theory, and I felt maybe I should say something about this pervasive notion that entropy is disorder. At a very technical level, the entropy of a system is the average number of bits you need to describe the state of the system. This is not an intuition gathered from stat mech, but what we call the 'operational interpretation' of the Shannon entropy. You can look up Shannon's noiseless coding theorem for a reference. The link to 'disorder' is more subtle. What does disorder mean? Well again in a very technical sense you might say that a system is more disordered if you have very little certainty if you try to guess its state. As it turns out, the uniform distribution maximises this uncertainty (or minimises the success probability of guessing). For a source regarding the above check 'min entropy'. As it so happens, the entropy itself increases as the distribution of a system comes 'near' the uniform distribution (in some suitable sense of 'near', see 1-norm between probability distributions). Now regarding your second statement that Landauer said entropy is information, actually what he argued is as follows: One needs to do work to set or reset the value of a bit. What you wrote is extremely confusing sonce you did not make clear the entropy of which system you are referring to. What I think you meant was that the 'bit' is a state of some system and one needs to do work to change the state of that system. And here you have a contradiction since this statement is decidedly untrue. One does not need to do any work to change the state of a quantum system, since one ks only allowed Unitary operations. This very much also extends to classical computation as well ( See Reversible Computation via Tofoli gates). So the actual correct (and accepted) interpretation of Landauer's statement is this: Any irreversible computation changes the entropy of a system. Since one needs to do work for irreversible computations that implies work changes the entropy of a system. This is provable (very easily) within the framework of quantum mechanics but none the less is cool.
For me it's that gravity has almost infinite reach, so we're technicaly connected to every star and black hole in the visible universe.
Every force has an infinite reach, though its strength diminishes quickly when you move away from the origin. That being said the magnets in your phone experience magnetic force due to a random magnetic field created from a random star in a random galaxy. So it's not only gravity.
If a sustained A note is playing in a soundproof room, and someone in the next room over opens the door so they can hear, but only for a very short time (~1 ms), the sound the person hears isn’t an A note, but rather, a combination of frequencies that doesn’t correspond to any one note.
Oobleck rigidifies because shear stress causes the suspended starch particles to form a network of frictional contacts, whose rigidity* causes a transition from a fluid to a solid. *in the sense of Maxwell constraint counting
That math shows no weakness in its ability to explain the universe.
Ok this one stopped me scrolling, can you tell me if I’m unpacking the poetic language fairly? I think by “math” you mean something like “our symbolic representation of relationships between quantities.” And by “explain” the universe you probably mean “describe” the universe, which avoids the issues around human comprehension. Is that about right? The boring implication here is that all our ignorance is due to (1) we haven’t discovered some relevant features, (2) we haven’t discovered some relevant math, and (3) we don’t find our mathematical descriptions to be satisfactory explanations (see prior paragraph). This doesn’t seem too controversial, but it doesn’t imply that we’re capable of overcoming these deficits (even if we don’t destroy ourselves before we have the opportunity). The more exciting implication is that math has some kind of universality, that no feature is beyond the ability for math to describe, that measurable quantities and relationships between them can be fully symbolized and systematized, yielding an all-powerful abstract model. I’m no philosopher so it doesn’t feel like I’m doing this justice. The absolutely mind-blowing implication is that math can describe possibilities that our particular universe doesn’t instantiate — maybe *all* the possibilities?! That math is powerful enough to describe more than just the possible relationships of our particular universe?! So if different constants or starting conditions are possible, math would still describe everything?! Just… yikes!
The fact that everything in theoretical physics points towards the idea that everything in the universe is a single object, inseparable of everything else. On the standard model there are like 19 objects, but almost every theory that has the potential of replacing the standard model reduces the number of objects of the theory.
42
This is the answer.
well, 42/2-3, according to the above.
Yeah! Materialist monism with degrees of freedom, baybay!!! 💥💥💥
quantum entanglement. This strange event occurs when two particles become coupled and one particle's state changes quickly.
Wave-particle duality. This just opened a new mind for me to look at the universe.
basically, particles behave according to probability distributions that look like waves. best way to put it.
Antimatter - and the sequence of events leading up to it: In a 1926 letter to Paul Ehrenfest, Albert Einstein wrote, "I am toiling over Dirac. This balancing on the dizzying path between genius and madness is awful". In 1928, Paul Dirac postulated the existence of positively charged electrons and in general anti-particles for every particle. The result was an equation describing both matter and antimatter in terms of quantum fields. 1932 Carl Anderson at Cal Tech discovers the positron in a cloud chamber FWIW I do think the whole matter/antimatter annihilation thing is very cool. As is the synthesis of Positronium, if only it had a longer half life. :)
Nonlocality. Relativity. These are both mind-blowing.
A ping pong ball can stand up to over 3000Gs of acceleration (0-450m/s down a 3m barrel ~= 33750m/s^2): https://i.imgur.com/lHNb8lC.mp4 You can build a jumbo model of a Paul Ion Trap (to trap charged dust) using a neon sign transformer: https://i.imgur.com/EJgg91N.mp4
The fact that black holes have a well-defined thermodynamics
Solving maxwells equations to derive the photon is pretty neat
You only need high school math. https://www.youtube.com/watch?v=h2ZKJWywggg
I think that it is cool that almost all matter (not Dark Matter) is PLASMA or gas. Condensed matter is comparatively rare.
Hook a wire coil to a milliamp meter, push a magnet in the coil and watch the meter give a reading. You are actually pushing subatomic particles (electrons) around. Think about that for a moment.
There aren’t enough different smell receptors in the nose corresponding to the number of smells that humans can identify. My lecturer was saying that the smell particle and the receptors may entangle with one another, transferring the information to the brain about the smell it’s detected?? Something like that. Was pretty cool it blew all our minds haha
Having never thought about it until 5 seconds ago, I'm guessing it's similar to looking at the light receptors in an eye and wondering if humans can see more than three colours
Yes, this is fairly close to the actual mechanism. The nose can detect a cubic bunch-ton of aromatic molecules but between nose and brain is an extra layer of cells (glomerulii) that act like an 'enhance video' trick and feed that 'smell image' to (various parts of) our brain for processing.
Sounds about right to me, that said: https://xkcd.com/793/
There was a very readable book detailing one wacky theory about how the sense of smell works, [The Emperor of Scent](https://www.goodreads.com/en/book/show/14546). Pretty sure it's largely inaccurate but was an interesting theory.
Most of the stars in the sky have planets orbiting them. It was only about 15 years ago that we learned that.
That the gravitational potential energy of the universe is negative and the matter content is positive. The total energy might well be zero.
Space (-time) can jiggle like jello. And we can measure the amount of jiggle.
I once made a list [here](https://www.pabr.org/scifactoids/scifactoids.en.html).
That gravity might not be a fundamental force, like electromagnetism, but instead an entropic effect, like a rubber band coming back to the smallest shape.
Everything travels at the speed of light. It's just that, if you have mass, most of that movement is through time. Floatheadphysics has [a great video](https://www.youtube.com/watch?v=TJmgKdc7H34) on this.
Best question on the internet today
THE BARKHAUSEN EFFECT: Hearing magnetic domains move! Copying an excerpt from Martin Gardner's book The New Ambidextrous Universe, Chapter 19 "The atoms in an unmagnetized bar of iron are not oriented in individually random ways. They tend to form little clumps or sets called domains in which the magnetic axes of the atoms are parallel. It is these domains, not the individual atoms, that have their magnetic axes turned in different directions. When the bar is magnetized by placing it in a strong outside field, the walls of these little domains shift as their atoms turn to align their axes with the axis of the outside field. The domains in the bar do not all swing into line simultaneously. As a result, the bar's magnetic field grows stronger in a series of abrupt little jumps. If a wire is wrapped around a bar that is being magnetized, each jump induces a small voltage in the wire. These electrical impulses can be amplified and actually heard as a series of clicks, a sort of rustling sound like that of paper being crumpled. This is called the Barkhausen effect, after Heinrich Barkhausen, a German engineer who discovered it in 1919. If you should visit the fabulous Museum of Science and Industry in Chicago, you can push a button and actually hear the Barkhausen effect. As you watch a small bar of iron move slowly into a magnetic field, you will hear the amplified rustling noise that results from the discontinuous movement of domain walls as the bar's atoms swing into alignment."
Nothing can escape the gravity of black hole, but it can emit Hawkins radiation proving that light can be a particle and a wave in different circumstances.
Gravity is not a force.
The human body generates more energy and heat per unit volume than the sun.
0K is the coolest physics fact
Bernoulli’s principle — essentially says that pressure plus velocity must remain constant. Velocity increases, pressure decreases to compensate; pressure increases, velocity decreases to compensate. It’s why planes fly and why people get pulled infront of trains if they stand too close.
Bernoulli's principle only applies to streamlines, so it doesn't really explain why airplanes fly. Watch this from 15:05-19:49 for a short, more nuanced look as to problems with using Bernoulli's law to try and explain lift: https://youtu.be/QKCK4lJLQHU?si=5GrHXee_fDzQOTT-
Infinity makes me uncomfortable ( or trying to imagine it too much), so the fact there is a physical limit of the observable universe is both beautiful, sad and comforting to me.
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Heating area outside of rusty bolt supposedly is key to freeing rust bolts threading but only works when you heat bolt directly instead 🤣🧐
[there are no particles. only fields.](https://pubs.aip.org/aapt/ajp/article-abstract/81/3/211/1032373/There-are-no-particles-there-are-only-fields?redirectedFrom=fulltext)
i believe that particles are viewed as the smallest possible perturbation of a field.
So what are fields then
Wave particle duality is the current understanding of physics, with waves and fields just being different words for the same thing. There’s quantum interpretations with only fields (https://en.m.wikipedia.org/wiki/De_Broglie–Bohm_theory) and interpretations with only particles where the waves are just statistically emergent behaviour (https://en.m.wikipedia.org/wiki/Ensemble_interpretation), but none of the interpretations have been proven correct
Quantum entanglement. Idea is just mind blowing.
Hong-Ou-Mandel intereference is a two-photon intereference effect. If you send two indistinguishable photons at a beam-splitter, they exit together instead of taking separate paths. See also [Wiki article](https://en.wikipedia.org/wiki/Hong%E2%80%93Ou%E2%80%93Mandel_effect) and [video](https://www.youtube.com/watch?v=BFIM5pHyd1k).
Magnets aren't about metals, or even attraction and repulsion but really its about how moving charges affect other moving charges A permanent magnet on a constant, uniform magnetic field, while being aligned with magnetic field direction, won't feel a thing
Coolest(literally) physics fact: coldest temp achieved in lab is 38 picokelvins, 38trillionth of a degree above absolutely zero. They had used a quantum gas lens and drop tower to create a BEC (Bose Einstein Condensate). It lasted for about 2 seconds.
Because of special relativity it is 100% possible to time travel into the future. There is nothing other than technology preventing us from doing it. Travelling into the past is a whole nother bucket of worms and may or, more likely, may not be possible.
Since the universe seems to be expanding, light emitted from stars that’s traveling to us has its wavelength changed over time. This is called Red Shift. The space that the light is traveling through is literally stretching the wave/particle as it expands
Not sure if this is necessarily physics related, but all music is math fundamentally and it makes me wonder about "good music" and it's relation to the numbers that orchestrate it.