The first nuclear clock will test if fundamental constants change
https://www.quantamagazine.org/the-first-nuclear-clock-will-test-if-fundamental-constants-change-20240904/- Let's assume they manage to make a nuclear clock out of this, with an Allan drift that's low enough to be useful. Once that's done, it'll take years of observation to measure any meaningful differences and gather enough data to notice something.
Meanwhile, moving the height of anything a centimeter, the position of the moon, and a whole other host of noise sources have to be canceled out.
I have no doubt this will be done... and it will be awe inspiring to hear it all told after the fact.
While you're waiting... I found this really cool meeting documented on YouTube[1] that has the clearest explanation of how Chip Scale Atomic clocks work I've ever seen.
I look forward to Chip Scale Optical Lattice clocks
[1] https://www.youtube.com/watch?v=wHYvS7MtBok
-- mikewarot Reply - Can't they do something similar to Ligo/Virgo setups? I.e. Multiple experiments running the same or similar hardware so that you can remove the type of noise you mentioned easily enough.
Additionally, this feels like it is much cheaper to deploy compared to the interferometer hardware used by those experiments, so you can put enough replicas around the world to cancel out any local source of noise.
-- marcyb5st Reply - > Meanwhile, moving the height of anything a centimeter, the position of the moon, and a whole other host of noise sources have to be canceled out.
Because time runs slower the stronger gravity becomes? I don't think it would be a problem, as long as the entire experimental apparatus is within the same gravity field for the duration of a particular measurement.
-- incompatible Reply - Optical lattice clocks are so precise these days, you can detect the difference in clock rates caused by a 2 centimeter difference in height. The higher clock will run faster.
In the famous thought experiment you can't tell the difference in an elevator in either a gravitational well, or accelerating frame. It turns out that is only true if the elevator is sufficiently small.
Sufficiently small is getting smaller every year.
-- mikewarot Reply - The lower gravity clock will run faster, but the experiment should give the same result, regardless of which frame it's running in. The same way that the caesium-133 atom transition frequency is 9192631770 Hz, regardless of the gravitational field.
-- incompatible Reply - The time shift of a Cesium beam atomic clock at different altitudes is a well established experimental result.
With Optical Lattice clocks, they are much more stable, and the output is light, so a phase difference can be detected much, much quicker. According to [1], a difference of 1 centimeter can be measured. The quote of interest:
An optical lattice clock with a frequency accuracy of 1 × 10^−18, which is currently the most accurate in the world, has a detectable gravitational potential equivalent to an elevation difference of approximately 1 cm.
If you can access it, here's the related letter in Nature[2] from 2018.[1] https://www.rd.ntt/e/research/JN202304_21619.html
[2] https://www.nature.com/articles/s41586-018-0738-2
-- mikewarot Reply
-- Reply- The gravity field we are in isn't that constant. The gravitational influence of the moon is strong enough to move a lot of water here on Earth. The other planets are a lot further away, but not completely without gravitational influence. Earth's orbit around the sun isn't a perfect circle and has ~3% difference between lowest and highest point. The seasonal shift in mass distribution on Earth is big enough that we used to correct for it in astronomical time observations (the up to 30ms or so between UT1 and UT2).
On the other hand, I don't think this experiment is really all that sensitive to gravity since we aren't really measuring time.
-- wongarsu Reply - But it would depend on how long it takes to make a single measurement. Perhaps the moon wouldn't move far.
-- incompatible Reply - I think you might mean the one _electron_ conjecture. It’s fun because you have anti-electrons whose Feynman diagrams look like electrons going backwards in time. So you could conceivably be observing the tangled world line of a single electron bouncing back and forward in time — sometimes observing it as an antielectron.
Doesn’t work with photons because there’s not an anti-photon.
Anyway it’s sort of a fun “woah!” moment that Feynman was so good at producing, but I don’t think it’s taken particularly seriously as a theory.
-- heisenzombie Reply - > Lots of nuclei have similar spin transitions, but only in thorium-229 is this cancellation so nearly perfect.
>
> “It’s accidental,” said Victor Flambaum(opens a new tab), a theoretical physicist at the University of New South Wales in Sydney. “A priori, there is no special reason for thorium. It’s just experimental fact.” But this accident of forces and energy has big consequences....
> Physicists have developed equations to characterize the forces that bind the universe, and these equations are fitted with some 26 numbers called fundamental constants. These numbers, such as the speed of light or the gravitational constant, define how everything works in our universe. But lots of physicists think the numbers might not actually be constant.
Putting these things together, if the physical constants do change over time, then perhaps there really isn't anything special about thorium-229, it's just that it's the one where the electrical repulsion and strong nuclear forces balance out right now. In a billion years maybe it would be some other element. Maybe we're just lucky to be alive at a time when one of the isotopes of an existing element just happens to line up like this.
Perhaps too there's an optimal alignment that will happen or has already happened when those forces exactly balance out, and maybe that would be an ideal time (or place, if these constants vary by location) to make precise measurements in the changes to these constants, much like a solar eclipse was an ideal opportunity for verifying that light is bent by gravity.
-- elihu Reply - Not a physicist, just a passionate layperson.
AFAIK real practitioners choose their units such that a lot of things are unity: speed of light is 1 (hence E = M), h-bar is 1, etc.
There are some numbers like the “fine structure constant” (which I think is tantalizingly close to 1/137) that do seem difficult if not impossible to derive from others.
The pop-science explanation for this that a layperson like myself would know about is the “anthropic” principal, they are such because only in such regimes would anyone ask the question.
I don’t know what real scientists think about this.
-- benreesman Reply - The speed of light will always be seen to be the same no matter what, no matter where you are, no matter when you are. That's because we measure the speed of light with light, and we measure distances using light or light-by-proxy (because the electronic interactions that make normal forces what they are... electronic and subject to the speed of light, as is everything else).
Other constants might change, but it would be very surprising if the speed of light (as observed locally) could possibly vary.
-- cryptonector Reply - c is no longer measured, it is defined, and unless some contradiction to special relativity is discovered, c cannot change. If the speed of causality changes, then our measure of distance would change. For example, if c halves in some sense, then this means light travels half as far during N ticks of a clock, and the meter will halve (and all internet latencies will approx double!). If we keep the old meter, then we might say c has changed; it's truly a matter of definition (and practicality) at that point.
-- simpaticoder Reply - Same goes for their new thorium “clock”. They define it as their unit to measure everything else. They assume that all constants may be changing but not their thorium clock. I think this is an unjustified assumption.
-- nyc111 Reply - If they detect that the change there would be a strong incentive replicating the setup as well as to put into scrutinity. Academia even with its faults is a very good institution for that.
-- JanisErdmanis Reply - Wouldn't a different speed of light impact the Schwarzschild radius of black holes of a given mass?
Assuming that you can create a standard clock, and given a black hole of standard mass, you can then measure speed of light in black hole radii per unit of time, which will differ with different speeds of light.
-- mattashii Reply - > Wouldn't a different speed of light impact the Schwarzschild radius of black holes of a given mass?
No it wouldn't. Our fundamental unit of distance (the meter) is defined in terms of the speed of light, so the radius will stay exactly the same, in meters.
-- orlp Reply - We can try to use gravitational waves (speed of gravitation propagation) to measure length.
-- oneshtein Reply - Gravitational waves travel at the speed of light as well. So if the speed of light changes, so would the speed of gravity waves, presumably - otherwise, they would probably not be equal today (though of course it could always be a coincidence).
-- tsimionescu Reply - Speed of light can also be derived from the speed of a signal through a length of wire.
-- mystified5016 Reply - I think the point is that if the speed of light changes, so does the length of the wire.
-- jon_richards Reply - Basically. I suppose that ε0 and μ0 could change in different ways such that c remains the same, or in different ways such that c does change but the change might be noticeable.
-- cryptonector Reply - You’re assuming a monotonous linear change. It could be periodic or jumping between discontinuous values.
-- vlovich123 Reply - Matter in other galaxies would behave differently from matter in the Milky Way if fundamental constants are not always true. I argue about this sometimes. Others keep stating that the wavelengths are equal, so everything else must be.
-- 1970-01-01 Reply - I think the better way to ask this question is: how much large scale spatial variation can there be in the laws of physics so that the observable behavior doesn't contradict existing observations? As far as I remember, this has been studied, but I can't find a reference right now.
-- gmueckl Reply - wikipedia has a high level review of current constraints: https://en.wikipedia.org/wiki/Time-variation_of_fundamental_...
fine-structure constant: less than 10^−17 per year
gravitational constant: less than 10^−10 per year
proton-electron mass ratio: less than 10^−16 per year
-- jepler Reply - [dead]
-- canadianfella Reply - Well, if you think about it, on a large scale of the universe, our laws are helped by our mathematical inventions of dark matter and dark energy. So is there really dark matter and dark energy, or is our understanding of the laws of the universe incomplete?
-- gitaarik Reply - Many, many, many scientists have asked this question. Many have made careers out of arguing the case.
But, the overwhelming majority of scientists that start out asking those questions ultimately land on the mainstream theories around dark matter and dark energy being our best, most consistent, and broadest ranging answers.
If someone were to come to them with a better theory that could explain more completely the sum total of these observations they would almost certainly be open minded about it.
So... is there really dark matter and dark energy? Probably. We've got a whole lot of evidence that isn't explained better by any alternatives. But I doubt any of these scientists would say it's totally impossible.
-- cthalupa Reply - Yes of course, it's the best theory we currently have. Also Newton's gravitational theory was the best explanation until someone came with a paradigm shift that explained the observations better. And we seem to be quite stuck with the current theories, so I suspect we might need another paradigm shift.
-- gitaarik Reply - As I understand it, dark matter and dark energy are just placeholders for discrepancies between our current physical model and observations made by telescopes like Hubble and Kepler. This could mean either that our measurements are inaccurate, or that the model is incomplete. Honestly, I think that both are extremely likely.
-- foxyv Reply - Dark matter (matter that has mass but does not interact in any other way) might be the literal solution. But there are also other suggestions (MOND is a big one).
The https://en.m.wikipedia.org/wiki/Bullet_Cluster is pretty interesting.
-- AlexAndScripts Reply - "Dark matter" and "dark energy" could just as well be called "unexplained matter" and "unexplained energy".
These terms are mostly placeholders for things we don't understand.
-- BurningFrog Reply - not even that.
"unexplained matter" implies that there is some matter to explain (what type etc) when in reality is an unexplained observation that could be explained by current laws/constants if only there was some more (actually a lot more) matter. is a pure mathematical construct and mathematically it wold be just as valid to ad "dark constant modifier"
-- cowl Reply - The mainstream thought is that they are real and undetected, but there are theories that they aren't and there's plenty of attempts to modify laws to explain them away (and I suspect there's some wistful thinking that there's maybe a Noble prize there, so there's already been a fair bit of work done, even though it's very controversial).
-- wisty Reply - Our understanding of the laws of the universe is incomplete either way. If dark matter exists, we still don't know what it's made of or exactly what properties it has.
-- roywiggins Reply - > So is there really dark matter and dark energy, or is our understanding of the laws of the universe incomplete?
These propositions are not mutually exclusive, the former implies the latter, right?
-- thewarpaint Reply - If the fundamental constants are not constant, why not expect them to change in this galaxy as well? The appeal to "other galaxies" seems suspect to me, a way to evade falsifiability.
-- mysecretaccount Reply - If the constants are the same in distant galaxies, then that's either a massive coincidence or the constants are stable over both time and space (because of lightspeed delay). The further away we look, the more obvious any effect should be.
If we detect a change then it's worth checking if this is also observable over shorter distances and timescales, and at that point we would look at our own galaxy.
-- wongarsu Reply - The galaxy is very small compared to the size the universe. If there were observable differences from 100k light years away (so just 100k years ago), the differences across billions of light years should be much more noticeable.
-- mr_toad Reply - "A way to evade falsifiability" is the goal of the statement, given that we've been searching for evidence to the contrary for as long as we've been able. We haven't found any, and we've searched close-at-hand the most thoroughly.
-- itishappy Reply - If the constants change over very long time spans, we could observe this by looking at distant galaxies from billions of years ago. We don’t have a way to make similar observations within our own galaxy.
-- mbrubeck Reply - What if the constants only changed over incredibly small scales, vibrating back and forth between two very similar numbers like a standing wave with extremely small amplitude and wavelength, such that any measurement done on even small scales has trouble seeing anything but the average?
-- lupusreal Reply - The idea is they're fixed/set by the overall size of the galaxy.
-- 1970-01-01 Reply - What's meant by "the wavelengths are equal"? (And have we measured comparable wavelengths in other galaxies?)
-- rkagerer Reply - Yes, we've measured comparable wavelengths. It's one way we can measure the red shift. Not just (red shifted) absolute wavelengths, but the relative spacing between them are quite sensitive to physical constants. These spectra can also be used for identifying the elemental composition of stars.
-- analog31 Reply - The wavelengths of physical processes are equal. If fundamental constants changed, we'd expect, say, the Lyman series to change too.
-- itishappy Reply - Presumably they mean propagating EM radiation we observe from earth appears to behave the same on earth as we observe from distant galaxies since the event that created them happened at a time much different than ours and a distant region of space.
-- fnordpiglet Reply - I mean, technically the EM radiation we observe from distant galaxies does look different than the EM radiation we observe locally: it's red-shifted.
I'm sure someone has proposed this is due to physical constants changing over time, rather than the expansion of space-time, and I'm sure someone else has explained why this is wrong.
-- saalweachter Reply - > What's meant by "the wavelengths are equal"?
Absorption lines of the elements in the stars whose starlight we observe. THey are the same after correction for redshift.
-- cryptonector Reply - Not necessarily. We have redshift and we use that to measure distance (in space and time). If fundamental constants were different in the past that might merely change only what distances we measure.
-- cryptonector Reply - One thing I have been arguing for a long time is that the fundamental constants are different until we observe them. i.e. if we don't observe it, it's possible for a tennis ball to travel through a wall. But in the universal program, if we will now or later observe the result, then it won't happen. But it'll happen so long as we will never observe the result. In fact, it's probably happened many times.
No one has proven that this is impossible, AFAIK.
-- renewiltord Reply - What does "impossible" mean to you if not that a thing and it's consequences can never be observed?
-- ezrast Reply - Impossible means it does not happen, not that it does not happen only when we look. Just because we can't see it doesn't mean that it doesn't happen. After all, as the comment I replied to pointed out, other galaxies can have different constants. We have to be humble and admit we just don't know.
-- renewiltord Reply - This seems like a distinction without a difference, since we can never positively categorize any unobserved phenomenon as impossible (vs merely unobservable). To me, it seems ontologically cleaner to treat existence and observability as the same thing. shrug
-- ezrast Reply - Okay, fine, I'll come clean, I was just making an unfalsifiability joke. The original god-of-the-gapsy comment was the one that got me. Always just out of reach of our verifiability is the magic. Why not all the way out?
-- renewiltord Reply - Whelp, looks like I'm today's Poe's Law poster child. ;)
-- ezrast Reply - The problem with these type of arguments is rigorously defining “we” and “look”.
Turns out that our gaze has no effect on anything and we’re uninteresting squishy bags of mostly water as far as physical processes are concerned.
-- jiggawatts Reply - Yeah, but no one has proven that this is impossible so it's still possible. Just like OP comment.
-- renewiltord Reply - https://www.smbc-comics.com/comic/2014-03-25
-- wizzwizz4 Reply - By "Observe" dont they mean the act of any photon "hitting/interacting with" the system collapsing it into a known/predictable state.
Not specifically a "intelligent" observer per se.
-- dmateos Reply
-- Reply- If the laws of physics can drift over time, might that explain the Big Bang?
-- BurningFrog Reply - I don't think so. There was no time before the Big Bang, so it's not like the laws of physics have anywhere to drift from such that they're in a bang-causing configuration at t=0.
-- __MatrixMan__ Reply - I think that’s an overly strong statement. There’s a theory that the Big Bang followed a Big Crunch from a “previous” universe [1]. Or our universe is a black hole within another higher dimension universe since the edge of our universe looks a lot like what we would think the event horizon looks like within a universe [2]
It’s correct to say that the time of our universe begins at the Big Bang, at least as far as we can measure it in any way and according to the currently dominant theories, but there are ways that it would make sense to talk about a time before the Big Bang and what caused it to happen.
[1] https://www.universetoday.com/38195/oscillating-universe-the...
[2] https://www.discovery.com/science/Universe-Inside-Every-Blac...
-- vlovich123 Reply - Big Crunch/Cyclic Universe theories are generally considered to be improbable based on our current understanding of the universe.
That there is no time before the big bang (possibly with some qualifiers to define the big bang, start of the universe, etc.) is the overwhelmingly prevailing view of modern cosmologists, from how I understand things.
-- cthalupa Reply - I think it would be clearer if such theories were described as claiming that a certain bang wasn't actually the big one.
I suppose these are equivalent, but one feels like a historical distinction while the other feels like a thermodynamic one and I think it's thermodynamics that contrasts the theories better.
-- __MatrixMan__ Reply - > There’s a theory that the Big Bang followed a Big Crunch
Does that theory come with a testable hypothesis?
-- toenail Reply - Most unfortunatly, there is the sawtooth cosmogony put forth by Joe Haldeman: if we harness the entire power of Jupiter converted to energy, and recreate the big bang, it's game over here, and everything restarts.
The test of course, trivizes,it. To destroy our universe, and the we know wheather, there is a steady state, a forever expanding, a saw tooth, or a wimper. ( see Dr Fred Hoyle), or, as our brains grow freely in epanded capacity, something so radically beyond our current comprehension that it will leave us in a pseudo-comoyose slack jaw state for a very long time.
"A watch maker, without ever opening a watch may make some very ingenious ideas about how a watch works, but without opening the watch, he may never know the truth." -Einstien
The big bang came with the presence of background radiation, in a non-uniform way pointing to the area in the Hercules constealtion. The crunch can come with a slowing of expansion or a change in the constants that hold our current paradiem together.
This work is seriously cutting edge.
-- ForOldHack Reply - Yes and it’s likely to be falsified. But us living within a singularity I believe is a consequence of string theory if I recall correctly.
-- vlovich123 Reply - To flesh out my thought, I'm thinking something must have changed to make the universe go from a previous stable state to the BANG state.
A weakening of some force keeping things together seems as likely as anything to me.
-- BurningFrog Reply - Many argue there is no "before" the bang state. Time and space might well have started with the big bang. There would be an absolute zero point in time, and nothing could be before that just like nothing can be colder than 0K.
For a while there was also the theory that the universe is cyclical: it eventually collapses and from that compressed state a new big bang is born. That seems very unlikely with what we know right now though.
Then there are various forms of the multiverse theory where are kind of spontaneously created in a continuous process. Each universe experiences a big bang in the moment it is created, so talking about "before the big bang" only makes sense outside the universe
But I don't think anything rules out a universe laying dormant and then something triggering the big bang either. Changing fundamental constants might well be that something. They don't even have to change continuously or frequently for this to work
As you might have guessed, testing any of these is really difficult. Not necessarily impossible, but really really difficult
-- wongarsu Reply - That sounds like a fine idea to me. I'm just trying to point out that if it's true, then that bang wasn't the big one.
We can have several very large bangs, but there can be only one Big Bang™, and nothing comes before it. This is for the same reason that Harry Potter is a wizard, it's not about evidence, it's just defined that way.
-- __MatrixMan__ Reply - If fundamental constants could change, this would violate energy conservation, and the second law of thermodynamics. Someone once said, if your pet theory violates the second law, there is no hope. Or am I missing something?
-- qsdf38100 Reply - Energy conservation isn't as sacred as many people (including me) assume. See for example https://www.preposterousuniverse.com/blog/2010/02/22/energy-...
-- tines Reply - And in fact, energy is not conserved (and cannot even be defined) globally in General Relativity. There is a different conservation law, called the conservation of stress-energy.
-- DiogenesKynikos Reply - Conservation of energy is the first law. I don't suppose anyone has any doubts about the second law?
-- kibwen Reply - The second law is not a law in the same way like the law of gravity is, it’s more a statistical statement. It simply states that more probable things will happen more often. How do we know what’s more probable? It’s what happens more often. It’s only inviolable insofar as we presume we know all the laws of nature.
Also, the second law is only applicable to closed systems. The universe may not be a closed system in the way we normally think of it.
-- tines Reply - The second law may be in a way we must evolve to conceive it, or may be in a way that we may never conceive it, or we are acting in ideas that are as distant as friction creating fire. We crawled, the we walked, then we ran, rode, motored, flew, rocketed, got stuck in orbit...
My college physics professor once said, "if in order to make progress we must leave reality, by all means let's leave reality." He also pointed to three red volumes on his shelf, and said those may interest you, and they did. (Richard Feynman)
-- ForOldHack Reply - My best guess at this moment is that all the fields can or may influence each other, resulting in relative changes.
Some things may seem incredibly constant, but have to be measured in such a ridiculous small or big (time) frame, that it's barely not measurable at all.
-- b3lvedere Reply - If it does change, for what ever reason, like, what does it actually mean?
Someone big brain explain to me why this is a big deal.
-- chadrustdevelo Reply - It basically invalidates modern science in the same way Einstein invalidated Newtonian physics. It would mean we have pretty good approximation on how things work, but we are fundamentally wrong. So it would be an exciting time to be a physicist, as it would force us to rethink how things really are from atoms, to stars and the beginning of the universe.
-- jasekt Reply - It does not invalidate science. The scientific method is the process by which we build gradually towards a clearer picture of the ground truth if there is one. Even if by “science” you just meant our current understanding of the universe as opposed to the method we gain that understanding, then this would not invalidate that, it only invalidates a small part.
Yes, we are fundamentally wrong, I would hope that all physicists recognise that we don’t have a perfect explanation for how things work yet, this would be just another step in that process, but an exciting one indeed.
-- left-struck Reply - Doesn't the fact that both General Relativity and Quantum Mechanics don't make correct predictions at all scales already show we're fundamentally wrong?
-- shiroiushi Reply - Maybe. Maybe not. There might not be a Universal Theory of Everything. Everyone hopes there's something and most scientists do believe that something is out there, but the idea that there might be reasons we can't unify them or that there are physical limits that prevent us from gathering the information we need to fully suss things out isn't exactly fringe science.
-- cthalupa Reply - It’s still something of an open question whether or not G is actually constant.
Not only that, but the results differ depending on whether atomic or dynamical time is used! In the latter case no change is measured using lunar reflectors.
-- User23 Reply - Remind me what are the dimensions of G?
-- ForOldHack Reply - "When you absolutely, totally, fundamentally, have to, fundamentally be sure" :)
-- Bluestein Reply - They probably do change, but extremely slowly. It would feel strange if there were something fixed in the universe.
-- mseepgood Reply - Why would it be "strange"? What reference can we possibly use to compare?
This sort of thing tends to be so far from "common sense" it probably doesn't make sense to try to reason about it from that perspective.
-- kimixa Reply - It's possible to measure the ratios of the constants, like mass_of_proton/mass_of_electron . Another is the fine structure constant, that is related to the charge of the electron (divided by a lot of other constants to cancel the units). Both of them are related to the spectral lines of the light emitted and absorbed by atoms, so if they changed the "color" of the other galaxies should have changed a little. https://en.wikipedia.org/wiki/Dimensionless_physical_constan...
-- gus_massa Reply - I know nothing about this: what if the color did change, to be slightly redder?
-- freeone3000 Reply - Then we ( and Hubble ) may over estimate the speed of the expansion of the universe, an the galaxies that we have measured their red shift and estimated their relitive speed based on less of a red shift. It is certainly possible.
-- ForOldHack Reply - The fossil reactor at Oklo https://apod.nasa.gov/apod/ap100912.html and https://en.wikipedia.org/wiki/Natural_nuclear_fission_reacto... can be used for that question.
From Wikipedia:
The natural reactor of Oklo has been used to check if the atomic fine-structure constant α might have changed over the past 2 billion years. That is because α influences the rate of various nuclear reactions. For example, ¹⁴⁹Sm captures a neutron to become ¹⁵⁰Sm, and since the rate of neutron capture depends on the value of α, the ratio of the two samarium isotopes in samples from Oklo can be used to calculate the value of α from 2 billion years ago.Several studies have analysed the relative concentrations of radioactive isotopes left behind at Oklo, and most have concluded that nuclear reactions then were much the same as they are today, which implies that α was the same too.
-- shagie Reply - Is there a good explanation of how that isn’t just measuring the expansion and contraction of a ruler with itself? Don’t we know the reactor is 2 billion years old because of radio dating?
-- User23 Reply - It would be somewhat hard to tell if there's circularity somewhere, but you should be able to date it somewhat with the quantity of oxygen in the atmosphere at various times and general geological processes.
-- Vecr Reply - No, those are separate processes.
The isotopes produced during the natural nuclear reactor 2 billion years ago were produced in certain ratios because of the relative sizes of their nuclear cross sections, which depend on the fine structure constant.
The isotopes used in radio dating are produced by spontaneous transmutation over time, which is governed by entirely different processes.
-- adastra22 Reply - No, because you’re comparing the various proportions, it’s like comparing the contraction of various rulers made from different woods.
-- thowawatp302 Reply - Well, it's dated against pulsars and stars. But those sources of information have a bit of an error bar on time-space distance.
Which is why a synthetic clock is needed here. That will have a known inception date and the changes if any can be compared.
The problem with both is they're not exactly fully closed systems anyway so there will be some margin of error ever with the length of the operation.
And during the test, we might just find out something completely unaccounted for in current physics... That isn't a universal constant related at all.
-- AstralStorm Reply - If nothing remains constant then there's no identifying feature to point at and conclude that my experience yesterday and my experience today occurred in the same universe. Surely that feels even weirder than letting there be something that can be used as primary key for universe identification.
-- __MatrixMan__ Reply - this is a bit tangential, but I once had a physics professor describe light waves as standing still and everything else is just moving around it.
-- jjeaff Reply - It's kind of silly to take the perspective of light, because it doesn't experience time (obviously, but you know what I mean). Maybe there will be new physics on that like there was with neutrinos, but it can't be too much of an effect.
-- Vecr Reply - > it can't be too much of an effect.
That is the problem with any argument for some new physics - it might exist, but it can't have much effect or we would detect it. Generally I only see people arguing for new physics because they really want faster than light travel (typically also without all the weird time effects, but a small minority would accept it with time effects)
-- bluGill Reply - Also many people want to find libertarian free will somewhere in new physics.
-- Vecr Reply - In case anyone else is curious about this fact: it has to do with time dilation. As your velocity through space approaches c, your velocity through time approaches zero.
Since photons move at c, they experience zero time between creation and destruction.
-- mystified5016 Reply - Brilliant. Your professor for saying that, and you for recognizing it's significance.
-- ForOldHack Reply - Makes sense really. If velocity is the derivative of position with respect to time and photons don’t experience time how would they have velocity?
It reminds me of my silly One Photon Conjecture. That is, there’s only one photon that pops in an out of space as required by coupling events. Since it doesn’t experience time saying it can’t be in two or more places at the same time isn’t meaningful!
-- User23 Reply - [dead]
-- underbooter Reply - Like the Planet Express ship? Sounds like professor Farnsworth.
-- ant6n Reply - well no, photons move at the speed limit of causality in this universe
they actually arrive slightly later than neutrinos to observers on earth because neutrinos just plow through virtually anything including stars and planets while photons have to travel the path affected by gravity
photons aren't affected by gravity directly because massless but their path, their limit of causality, is affected
-- ck2 Reply - Even if it had a rest frame, Schrödinger is a pain.
An object at full rest is according to its wave/path equation literally everywhere at all times.
However superconductivity has a bunch of truck sized holes for this. Specifically we don't quite understand Bose-Einstein condensate completely. Funky entities like time crystals appear in the mathematics, etc.
-- AstralStorm Reply - [dead]
-- underbooter Reply - The most recent Kurzgesagt video (on time travel) https://youtu.be/dBxxi5XAm3U had this passage:
> To explain how this actually works without making a math video, we have to make a lot of physicists grumpy, so please keep in mind that we are simplifying and lying a bit.
And that simplification / lie is that everything moves at the speed of light in spacetime. We are moving at basically 0 in the space coordinates and 1s/s in the time dimension (which is "light speed" in the time dimension). However... (1:45 in the video)
> Photons, light particles, move at the speed of light through space. They don’t experience any
time passing because their speed in that time dimension is 0. In the time dimension they are frozen in place. If you see light on earth, from the photon’s perspective it was just on the surface of the sun and then suddenly crashed into your eye with nothing happening in between.... and this falls into the Lie-to-children domain. https://en.wikipedia.org/wiki/Lie-to-children#Examples_in_ed...
-- shagie Reply - Yeah isn’t it a simplification of the idea an object at rest has has a four-velocity where U^0 = c (so a velocity of c entirely the time direction) but a photon doesn’t have a rest frame to do this calculation?
-- thowawatp302 Reply - If they changed in a way to have meaningful impacts on how astronomical bodies operate we should be able to observe the change as some of the oldest light we observe is billions of years older than the newest light.
In fact, based on this we can tell that the fundamental constant the speed of light has not changed which I agree is very strange.
-- bitmasher9 Reply - It comes down to what time is. I.e. what was before the Big Bang? If time didn’t exist before big bang, then speed of light emerged after big bang, and as such “changed”.
-- vl Reply - Either there is some unversal constants, or everything constantly change.
-- psychoslave Reply - Could be both. Some things determined by some mathematical constraints will always be followed. Ex things like group theory and statistics will always be followed by any object subject to them, but how that manifests if the objects those rules act upon changes in form
-- hughesjj Reply - Most so called fundamental constants appear in the relationships between physical quantities only as a consequence of choosing arbitrary units.
It is possible to eliminate almost all fundamental constants by choosing so-called natural units for the base physical quantities, for instance the elementary charge as the unit of electric charge.
For all fundamental constants that can be eliminated by choosing natural units it makes no sense to discuss about changes of them.
Nevertheless, even when a natural system of units is used, there remain 2 fundamental constants (plus a few other fundamental constants that are used only in certain parts of quantum field theory).
The 2 important fundamental constants that cannot be eliminated are the Newtonian constant of gravitation, which is a measure of the intensity of the gravitational interaction, and a second fundamental constant that is a measure of the intensity of the electromagnetic interaction, which is frequently expressed as the so-called constant of the fine structure.
The meaning of the constant of the fine structure is that it is the ratio between the speed of light in vacuum and the speed of a charged particle with unit charge, like an electron, that rotates around another charged particle with unit charge, which is much heavier, like a nucleus, in the state with the lowest possible energy, i.e. like the ground state of a hydrogen atom, but where the nucleus would have infinite mass. The speed of the rotating particle is a measure of the strength of the electromagnetic interaction between two elementary charges.
So the only fundamental constants for which there could be a evolution in time are those that characterize the strengths of the electromagnetic interaction and of the gravitational interaction (and also the fundamental constants that characterize the strengths of the nuclear strong interactions and nuclear weak interactions).
The values of these fundamental constants that characterize the strengths of the different kinds of interactions determine the structure of the Universe, where the quarks are bound into nucleons, the nucleons are bound into nuclei, the nuclei are bound into atoms, the atoms are bound into molecules, the molecules are bound into solid or fluid bodies, which are bound by gravitation into big celestial bodies, then into stellar systems, then into galaxies, then into groups of galaxies.
Any changes in the strengths of the fundamental interactions would lead to dramatic changes in the structure of matter, which are not seen even in the distant galaxies.
So any changes in time of the true fundamental constants are very unlikely, while changes in the constants that appear as a consequence of choosing arbitrary units are not possible (because such fundamental constants are fixed by conventions, e.g. by saying that the speed of light in vacuum is 299,792,458 m/s).
-- adrian_b Reply - In natural units, the Newton gravitational constant can be set to 1 as well.
You do still need a term to characterize the strength of gravity. They sometimes use η, which can be defined in terms of G, c, Planck's constant, and a fundamental mass like the electron. The result is a truly fundamental unitless constant.
The Standard Model has a dozen or so other fundamental constants, describing various mixing angles and fundamental masses (as ratios).
-- jfengel Reply - Nope.
While the Newton gravitational constant can be set in theory as 1, it cannot be set in practice.The so-called Planck system of units where Newton's constant is set to 1 is an interesting mathematical curiosity, because in it all the physical quantities become dimensionless.
Nevertheless, when Newton's constant is set to 1, the number of fundamental constants is not reduced, but another constant that was 1 in other systems of natural units becomes a fundamental constant that must be measured experimentally, for instance the elementary charge.
Besides not having any advantage, because the number of fundamental constants in non-nuclear physics remains 2, the system where Newton's constant is set to 1 cannot be used in practice.
The reason is that the experimental measurement of Newton's constant has huge uncertainties. If its value is forced to be the exact "1", then those uncertainties are transferred to the absolute values of all other physical quantities. In such a system of units the only values that would be known precisely would be the ratios of two quantities of the same kind, e.g. the ratios of 2 lengths or of 2 masses. Any absolute value, such as the value of a length or the value of a mass, would be affected by huge uncertainties.
So the use of such a system of units is completely impossible, even if it is mentioned from time to time by naive people who know nothing about metrology. The choice of units for the physical quantities cannot be completely arbitrary, only units that ensure very low uncertainties for the experimental measurements are eligible.
Currently and in the foreseeable future, that means that one of the units that are chosen must be a frequency. For now that is the frequency corresponding to a transition in the spectrum of the cesium atom, which is likely to be changed in a few years to a frequency in the visible range or perhaps in the ultraviolet range. In a more distant future it might be changed to a frequency in a nuclear spectrum, like this frequency that has just been measured for Th229, if it would become possible to make better nuclear clocks than the current optical atomic clocks, which use either trapped ions or lattices of neutral atoms.
Some of the parameters of the "standard model" are fundamental constants associated to the strong and weak interactions. It is debatable whether it makes sense to call as fundamental constants the rest of the parameters, which are specific properties of certain objects, i.e. leptons and quarks.
-- adrian_b Reply - What about the constants that describe the (relative) rest masses of elementary particles? Since we don’t know the order of magnitude of neutrino masses, it seems improbable that even an order of magnitude change of those masses over time would lead to “dramatic changes in the structure of matter.”
-- addaon Reply - The masses of the particles and other specific properties, like magnetic moments, are not fundamental constants.
They are the properties of those particles. There are such properties for leptons, for hadrons, for nuclei, for atoms, for molecules, for chemical substances, for humans and so on.
Any object, either as small as an electron or as big as the Sun is characterized by various numeric properties, such as mass.
The fundamental constants are not specific to any particular object. As I have said, after eliminating the fundamental constants that are determined by conventional choices of the system of units, the only fundamental constants that remain are those that characterize the strength of each fundamental interaction, as expressed in a natural system of units.
Because most objects are composed of smaller subobjects, it should have been possible to compute their properties from the properties of their components. Starting from the properties of leptons and quarks, it should have been possible to compute the properties of hadrons, nuclei, atoms, molecules and so on.
Unfortunately we do not have any theory that can compute the desired properties with enough precision and in most cases even approximate values are impossible to compute. So almost all properties of particles, nuclei, atoms or molecules must be measured experimentally.
Besides the question whether the fundamental constants can change in time, one can put a separate question whether the properties of leptons and quarks can vary in time.
Some of the properties of leptons and quarks are constrained by symmetry rules, but there remain a few that could vary, for instance the mass ratio between muon and electron. It is likely that a future theory might discover that this mass ratio is not an arbitrary parameter, but the muon is a kind of excited state of the electron, in which case this mass ratio could be computed as a function of the fundamental constants, so the question whether it can vary would be reduced to the question about the variation of the fundamental constants.
-- adrian_b Reply - I think you are wrong; for example the Standard model has 26 (or 25?) fundamental constants that can be made dimensionless, so they are not dependent on the choice of units. Also, the masses of fundamental particles are connected to the strength of the coupling of the particle's field to the Higgs field, and those coupling strengths are fundamental constants.
-- GolDDranks Reply - [flagged]
-- bustergpt Reply