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Confused about Aether

  1. May 1, 2008 #1
    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.
  2. jcsd
  3. May 1, 2008 #2
    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.
  4. May 1, 2008 #3
    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?
  5. May 1, 2008 #4
    Thats exactly what the michelson and morley experiment did, again, disproving the existence of an ether.
  6. May 1, 2008 #5


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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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  7. May 2, 2008 #6
    The aether has essentially been replaced by quantum field theory in which all particles are excitations of a quantum field, be it the EM field in quantum electrodynamics or the "strong" field in quantum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 occuring in less than a Planck Time in one observer's frame, what is occuring 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.
  8. May 2, 2008 #7
    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.
  9. May 2, 2008 #8
    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.
  10. May 2, 2008 #9
    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.
  11. May 2, 2008 #10
    Well, i think we can both agree that Jennifer is incorrect... Or course the laws of physics are invariant... thats 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.

  12. May 2, 2008 #11
    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.
    Last edited: May 2, 2008
  13. May 2, 2008 #12
    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".
  14. May 3, 2008 #13
    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.
  15. May 3, 2008 #14
    einstein concluded that, indeed, there is an ether under GR, which he explained in a paper from 1920. you can read it here: <crackpot web site deleted>
    Last edited by a moderator: May 3, 2008
  16. May 3, 2008 #15


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  17. May 5, 2008 #16
    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.
  18. May 5, 2008 #17
    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.
  19. May 5, 2008 #18


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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..
    Last edited: May 5, 2008
  20. May 5, 2008 #19
    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.
    Last edited: May 5, 2008
  21. May 5, 2008 #20


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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 travelled a longer spatial distance than the one staying behind?
    Last edited: May 5, 2008
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