Confused about Aether

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nuby
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Confused about "Aether"

What is Aether supposed to be now days (and in Einstein's day)? Isn't Aether just space and time (and maybe their fluctuations)?

I thought it was simply a "media", which bosons and fermions travel on.
 

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  • #2
lzkelley
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The aether was the medium through which they believed light traveled. The presence of the aether implied an absolute reference frame - but the whole thing was disproved by Michelson and Morley about a century ago.
The general belief is that there is no aether.
Somewhat analogously i think space and time can be kind-of seen as a aether - but the big difference is that space-time we know know to be a very dynamical entity -> i.e. it still doesn't depict any absolute reference frame. A theoretical aether (again we don't think there actually is one) would be a medium, not the phenomena or fluctuations through/in/on/with that medium.

I think there are some theories that suggest there is some sort of aether or another; in general, there will always be some theory that predicts there is some sort of everything.
There is no experimental evidence to confirm or (to my knowledge) even suggest an aetheral existence.

I think it is interesting to note however, that because of quantum entanglement, there might be some sort of inextricable link between "distant" parts of space.
 
  • #3
nuby
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I'm surprised there hasn't been any recent experiments related to ether theory.. If Aether exists wouldn't light have a different velocity in a vacuum on earth, compared to the vacuum of space (due to gravity), as well as varying directional velocities (if the universe/ether is expanding in a certain direction). How hard would it be to perform experiments like this?
 
  • #4
lzkelley
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Thats exactly what the michelson and morley experiment did, again, disproving the existence of an ether.
 
  • #5
jtbell
Mentor
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See the FAQ on the http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html" [Broken]. Section 2 lists aether-related experiments that were done before Einstein, and Section 3 lists experiments that have been done since then.
 
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  • #6
peter0302
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The aether has essentially been replaced by quantum field theory in which all particles are excitations of a quantum field, be it the EM field in quantum electrodynamics or the "strong" field in quantum chronodynamics.

Unfortunately these theories don't really attempt to reconcile such pesky concepts like Lorentz-invariance. For example, they say that, within a Planck Time, random particles can pop in and out of the vacuum without violating conservation of energy. But if vacuum fluctuations are occurring in less than a Planck Time in one observer's frame, what is occurring in the frame of a relativistic traveller, who believes other people's clocks are running slower (and hence, longer than a Planck Time)? Is conservation of energy being violated for some but not others? It's obviously absurd.

Thus I don't think any aether theory is useful for anything other than a mathematical model.
 
  • #7
lzkelley
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That doesn't make any sense.
The reason virtual particles are allowed to "pop" into existence is because of the uncertainty principle -> i.e. DelP*DelT > h or so. And make sure to note that DelT goes (very roughly, and only in the general case - but adequate for us) inversely proportional to T.
Say for instance, in a virtual particles rest frame it "exists" for 10^-15s; If you are moving relativistically relative to the virtual particle, is that time going to increase or decrease (in your moving perspective)?
Now that you've answered "decrease," you see that the uncertainty principle holds even better in a moving reference frame.

The aether has absolutely been REPLACED by field theory (numerous kinds); field theory is not an adaptation of aether - its not building off of the same thing; its a replacement. The aether theory is useless, and none-nonsensical MATHEMATICALLY, and although it probably shouldn't be used at all - it might be somewhat useful to still imagine that there still is an aether, for introductory physics students.
 
  • #8
peter0302
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Say for instance, in a virtual particles rest frame it "exists" for 10^-15s; If you are moving relativistically relative to the virtual particle, is that time going to increase or decrease (in your moving perspective)?
Now that you've answered "decrease," you see that the uncertainty principle holds even better in a moving reference frame.
Um, I would have answered increase. Time 'dilates' - the moving clock runs slower. So in my moving perspective, the particle that exists for 10^-15s from Earth's perspective exists for quite a bit longer in my timeframe.

It's the same idea as muons decaying more slowly as they bombard the atmosophere because they're moving so fast. They're existing for much longer than they "should." So in a moving frame, a virtual particle on Earth could exist longer than it should.
 
  • #9
MeJennifer
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It's the same idea as muons decaying more slowly as they bombard the atmosophere because they're moving so fast. They're existing for much longer than they "should." So in a moving frame, a virtual particle on Earth could exist longer than it should.
This is incorrect, muons always decay at the same rate, how a muon moves in relation to an observer is obviously not going to make any difference. It is one of the first principles of the theory of relativity that the laws of physics are the same in all inertial frames of reference, and that includes the (average) time it takes for an elementary particle to decay.
 
  • #10
lzkelley
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Well, i think we can both agree that Jennifer is incorrect... Or course the laws of physics are invariant... that's the exact reason why muons decay slower when they are moving relative to the observer.

Anyway; i explicitly said a moving observer and stationary virtual particle.
If you say that the particle is moving at relativistic speeds, then you have additional issues because its energy is drastically increased. If its energy is drastically increased to a stationary observer, then it must exist much shorter than the same particle also stationary. Because its existing for a shorter period of time in the stationary reference frame, its existing longer in its own frame -> corresponding to its smaller energy in its own frame.
And bingo, lorentzian invariance is preserved.

Cheers
 
  • #11
MeJennifer
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Of course the laws of physics are invariant... that's the exact reason why muons decay slower when they are moving relative to the observer.
You are completely contradicting yourself here.

Fact is that observers in relativity all have their own proper time, and one observer's elapsed proper time is not necessarily the same as another. But that does not imply that physical processes go slower. They all go at a rate of one second per second.
 
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  • #12
lzkelley
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Nice try to switch this into a debate over semantics... i will not be misdirected! ;-)

While what i said might be a blatant contradiction to the laymen; it is of course logical to those who have explore the thought experiment derivations of special relativity. For physical laws to be invariant under Lorentz transformations, there must be discontinuity (although superficial) between observers in different reference frames.

Physical processes most certainly do go slower in a moving reference frame, relative to a stationary one. If for no other reason, this is implied by fundamental nature of the speed of light, and the observational truth that all gauge bosons travel at that speed. If photons (w and z bozons, gravitons, and gluons) travel at the same speed - invariant of reference frame - then the E&M (weak, gravity, and strong) forces must act more slowly in moving reference frames.
All physical processes are governed by these forces (if you didn't know), therefore, all physical processes are slowed in moving reference frames.

Note the longer lifetime of particles in particle accelerators; q.e.d.
"They all go at a rate of one second per second" is the moot-point to end all moots! Thats the kind of argument a social studies major would give... For instance, if you look up the scientific definition of a second... its defined relative to the actions of light, or the vibrations of crystals depending on your source and time period -> both of which are determined by the local reference frame --> therefore a second is not always a second, and a rate of ___ per second is not always ___ per second. But you are right, in one reference frame, one second will be one second (example, try checking your clock, then checking it again).

peter: look into the casimir effect or hawking radiation as evidence of virtual particles "popping".
 
  • #13
MeJennifer
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lzkelley, what you do not seem to realize is that if two clocks from different reference frames show a different elapsed time it does not imply that one clock goes slower than the other, they both go at the same rate!

It just means that one clock's one path in spacetime was longer than the other. The path length in spacetime between two events is the amount of accumulated proper time.
 
  • #14
jnorman
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einstein concluded that, indeed, there is an ether under GR, which he explained in a paper from 1920. you can read it here: <crackpot website deleted>
 
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  • #16
lzkelley
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lzkelley, what you do not seem to realize is that if two clocks from different reference frames show a different elapsed time it does not imply that one clock goes slower than the other, they both go at the same rate!

It just means that one clock's one path in spacetime was longer than the other. The path length in spacetime between two events is the amount of accumulated proper time.

A rate is a ration of measurements. If the ratio of measurements are different (clearly, as you say for instance with longer / shorter paths - noting that the other measurement is the constant speed of light) then the rates are different. q.e.d.
 
  • #17
MeJennifer
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lzkelley, when you and I go from A to B and I take a shortcut in space would you conclude that because my odometer shows less elapsed miles mine runs slower?

Only ether theorists stick to the idea of an absolute time. In relativity there is no absolute time, it is simply nonsense to say that one clock goes slower than another clock al properly working clocks go at the same rate.
 
  • #18
ehj
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You are self-contradicting MeJennifer. You say that there is no absolute time in relativity, which is true, but afterwards you say that all working clocks go at the same rate? That is exacty what absolute time is, that all clocks go at the same rate.
Two "properly working" clocks that are moving relative to one another will not go at the same rate. I think what you're basically saying is that a clock relative to itself will always tick at 1 sec per second, which is quite obvious..
 
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  • #19
MeJennifer
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You are self-contradicting MeJennifer. You say that there is no absolute time in relativity, which is true, but afterwards you say that all working clocks go at the same rate?
That is not a contradiction.

You obviously do not realize that events in spacetime are separated in 4 dimensions. If two observers go from A to B in a different way they could record a different amount of elapsed time for instance in the case of the twin pseudo-paradox. Not because one of the clocks went slower but because it simply took less time to go to B for one observer.
 
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  • #20
ehj
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I'm quite aware, that events in spacetime are separated in 4 dimensions.. I'll try writing what I get from what you're saying.
We're looking at two events A and B from two different frames, S and S' where S is stationary relative to us. If we look at the twin-"paradox" A can be the departure of the spaceship from the earth, and B can be the arrival back at the earth. The two events A and B are colocal in both S and S', they happen at the same place but are separated by a certain amount of time. And then you're saying that the difference in the elapsed time of the journey is due to the fact that the twin in the spaceship traveled a longer spatial distance than the one staying behind?
 
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  • #21
MeJennifer
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Actually the twin in the spaceship traveled a shorter path length in spacetime between the two events they have in common, hence the total accumulated time on his clock is less than that of the twin who stayed on Earth who has the extremum path length. His accumulated time is less which does not imply his clock went slower he just experienced less time.
 
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  • #22
ehj
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Hmm.. Have you seen the time-dilation formula? And how would you explain that formula without saying that the moving clock ticks slower than the one in rest?
The formula is: t = T*sqrt(1-(v/c)^2) where t is a proper-time interval and T is the coordinate time interval.
 
  • #23
mitesh9
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What man?

Ok guys,

Consider this (u might have come across this by the way!)...

There are two frames of reference S and S', in relative motion with velocity v. As none of them can be considered stationary (principle of relativity, all frames are equivalent), how can we choose wether the time is slowed down in S or S'? We can not. However, If we are in S, clock in S' would be slow for us (observer), however, if one of us is in S' instead, for him, our clocks are slow. That means, both clocks are slow, for the observer in other frame. However, that does not mean, that, any watch has actually slowed down due to it's speed. I think that's the point Jeniffer is trying to make (and is correct by me).

In fact, it is absurd to say that, "moving clocks slow down"! In SR, you can not say that any thing is moving. It is impossible to judge at all, wether anything is moving or not. The movement simply means motion relative to observer, and hence either the observer is moving or the event being observed is moving.

regards,

Mitesh
 
  • #24
Ken G
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I also agree with MeJennifer, and with mitesh9's effort to achieve rapprochement, on the topic of "slowing clocks", that it is in many ways a cleaner picture to simply say that a clock that measures less time actually experienced less time-- the rate of ticking being the same as it always is for good clocks. However, before we get too deeply into arguing that point, we'd better make sure we are distinguishing some pretty important issues.

There are two very different situations where one may wish to compare times. One is when both clocks of interest are inertial, so we expect all of special relativity to apply, but then the two clocks cannot both begin and end their journeys at the same two events (and get anything interesting). So we will always run into the issue of comparing times between different events, and thus we must take care we are not just talking about some arbitrary coordinatization (typically, we will be). We will probably use the Einstein simultaneity convention, but when we come up with different numbers for times elapsed, what does that actually mean that isn't just a function of our simultaneity convention?

Alternatively, we could talk about two clocks that make journeys between the same two events, so there is an obvious way to compare the times elapsed, but then at least one of the clocks must be noninertial (to get anything interesting). That means we must apply special relativity with utmost care, because in its rawest form, special relativity must be applied to inertial clocks. The way that's normally done is to track what the noninertial clock is doing by linking it to a succession of inertial clocks that share its motion briefly, but note since these clocks are continually changing, they must still be synchronized somehow, and so we still do not avoid the problem of coordinatization.

In short, it is very easy to think you are arguing physics in this kind of situation, when in fact you are just using a different way of coordinatizing and mistaking the results for something real that can be argued. In my experience, when that is the case, both parties can be perfectly correct, sound like they are completely at odds, and really just be arguing a personal preference for how to look at things. This may be the deepest of all the lessons of relativity, and I do believe that is happening above, for example.
 
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  • #25
ehj
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I agree with you MeJennifer, and Ken G that clocks don't "mechanically" slow down, but actually experience less time. The problem is the notion of two clocks' "rates". I would consider their "rates" as the ratio of the time they experience. Although I think what you mean with their rates is that a second on one, is a second on the other when they are at rest relative to each other. You're pointing out, that the cause for the decay-experiment's result, is the time dilation between the two frames. I misunderstood you :)

Although Mitesh9 seems to have raised some questions with me..
I'd say that any frame can be considered, emphasis on considered, stationary, which is what we're doing when saying "we are in S", which you do yourself. What you can't say is that a frame "is" stationary, in some absolute sense - because of the the relativity principle.
"However, that does not mean, that, any watch has actually slowed down due to it's speed."
I don't quite know what you mean with "actually". You can't say what "actually" happens, only what happens from a certain frame. The clock's are mechanically identical, and will therefore tick at the same rate when at rest with each other, but differently when moving relative to each other, if the rate is considered as the ratio between the experienced time of the two clocks. I think I agree with your point though, that "clocks slow down" is a term lacking information about what you actually mean.
 
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  • #26
mitesh9
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I agree with you MeJennifer...

Although Mitesh9 seems to have raised some questions with me..
I'd say that any frame can be considered, emphasis on considered, stationary, which is what we're doing when saying "we are in S", which you do yourself. What you can't say is that a frame "is" stationary, in some absolute sense - because of the the relativity principle.
"However, that does not mean, that, any watch has actually slowed down due to it's speed."
I don't quite know what you mean with "actually". You can't say what "actually" happens, only what happens from a certain frame. The clock's are mechanically identical, and will therefore tick at the same rate when at rest with each other, but differently when moving relative to each other, if the rate is considered as the ratio between the experienced time of the two clocks. I think I agree with your point though, that "clocks slow down" is a term lacking information about what you actually mean.

Well, "actually" means, literally actually. A clock in my own frame is actual clock for me, while the one in another reference frame in relative motion with me is relative clock for me. To further clarify, I would say, as there is no frame which "is" at rest, and as all frames are equivalent, their "tick rates" are also equivalent. When we say a clock has slowed down, it actually translates to "it appears slow to the observer in other frame (of course in relative motion!)".

That means, If I get aboard a spaceship with a clock, and travel at c (impossible it may be), yet my heart will beat and the clock will tick. I will age and subsequently die, however, to an observer (relative to whom I am moving with velocity c) will find that I am not aging at all! Note that, this is directly contradicting to the muon phenomena, in which the muons actually reach the surface of the sea (surviving more then their lifetime), but let's not get into that (I don't understand it :smile:).

Regards,

Mitesh
 
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  • #27
ehj
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It doesn't seem to be in contradiction with the muon phenomenon. As I would observe you to age less, the muons age less and thereby decay later than if they were at rest relative to the earth.
 
  • #28
mitesh9
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Yes, it seems true, but I can not somehow get the feeling of understanding it (or digesting it), because, the muons just don't appear to decay slow, the experiment tries to prove, that they actually decay slow, and we detect the muons in our frame of reference (earth) on the surface of the sea, which is of course stationary with respect to us. The muons are created in atmosphere, which is also our own frame of reference and stationary with respect to us.

This is comparable to the twin paradox, where, the astronaut twin was in our frame of reference, travels and comes back to our frame of reference, and is aged slow. If this is considered a paradox, and we need to give all sorts of explanations regarding acceleration and de-accelerations, and change of frames, the same applies to muons, which are created on earth, travels at relativistic speed (changes their frame of reference) and comes back to Earth (sea), but we just agree to it!
 
  • #29
matheinste
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As ehj says the muons age less and so decay later. This of course translates to "from our earthhbound point of view the muon's clock ticks more slowly than ours".

Of course from the muon's point of view the distance it travels before decay is shorter than perceived by us..

Mateinste.
 
  • #30
mitesh9
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Of Course I know about mathematical treatment of the problem, from both sides, however, tell me something about the twin paradox analogy of the muon problem.

regards,

Mitesh
 
  • #31
peter0302
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peter: look into the casimir effect or hawking radiation as evidence of virtual particles "popping".
Oh, yes indeed I am aware of these effects. What I don't understand is how they don't violate CoE. And more specifically, since a particle existing for a Planck Time in frame A exists for longer than a Planck Time in moving frame A', and we know that CoE cannot be violated in ANY frame or else the laws of physics would not be the same, how is this apparent paradox answered?
 
  • #32
matheinste
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Hello mitesh.

There is no paradox. There is a perfectly logical explanation within SR but some say that GR is required.

Matheinste.
 
  • #33
mitesh9
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Sure!
But my question is, How is twin paradox (may it not be paradox) different from muon situation? and if they are not different, why do we need to give explanation for the former, while accept the later as it is?
 
  • #34
Ken G
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As ehj says the muons age less and so decay later. This of course translates to "from our earthhbound point of view the muon's clock ticks more slowly than ours".
This is indeed a commonly used phrased, and I said above one cannot say that it is "wrong", because it all depends on certain coordinate choices. Nevertheless, I like to point out that this is not a necessary way to say it, nor even the best way in my opinion, for I prefer saying "the time between the events of creation and destruction of the muon, in our earthbound point of view with the Einstein convention, is longer than is that time in the muon frame". There is no need to specify a reason for this fact that has anything to do with what is happening to time, other than a result of the relative velocity between the frames, as any reason you cite will merely be exposing a choice of coordinate.

It is the same as if I asked you why light passing from one rocket to another might be redshifted-- there is no unique reason (in special relativity) other than "they are separating". In the above example, if we say one clock ticks more slowly as viewed from another, we are still exposing a prejudice that the time elapsing in our frame is in any way relevant to the time elapsing in some other frame. An important lesson of relativity is to relax that assumption, so why underscore it with our terminology, even if all we mean by "rate" terminology is dividing some other time by our own time? What is the meaning of such a ratio other than a comparison of two times, one being larger than the other?
 
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  • #35
mitesh9
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By the way, In addition to my previous post, can anyone tell me what is the perfectly logical explanation for the (so called) "twin paradox" too? And what is the true (may not be logical, like SR), explanation for it?
 

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