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Author Topic: Why no Æther  (Read 8564 times)

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Offline acsinuk

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Re: Why no Æther
« Reply #25 on: 04/01/2012 07:57:14 »
Shrunk
Yes, I think that space is not empty as Einstein envisaged; this is because free space has a magnetic permeability constant that does not appear in any of the gravitational attraction equations.  If space is magnetized then transmission of electromagnetic light is possible; if not magnetized then no medium is there to transmit the light.  Happy new year
CliveS
 

Offline JP

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Re: Why no Æther
« Reply #26 on: 04/01/2012 09:35:15 »
I can't see what's so scientific about claiming something doesn't exist on the basis that it can't be detected. If nothing could travel faster than the speed of sound because all the forces between atoms acted at the speed of sound, accelerating something up towards the speed of sound would automatically slow down any kind of clock you tried to devise and contract things in the direction of travel, and if it was also impossible to detect the air directly, you'd have the same kind of situation in which many scientists would step beyond their competence and declare that the air does not exist, all based on an experiment (Michelson-Morley) which fails because the equipment is contracted by its own motion through the medium it's trying to detect. Claiming that that aether doesn't exist on the basis of MM is philosophy, not science.
Well, at least the newbie is on my side. Thanks for your support, David.

Again, this is an argument that amounts to moving the goalposts by redefining aether.  The aether theory assumes the speed of light isn't constant and therefore time dilation and length contraction don't exist.  If you redefine things so they both exist from the start, then you're not dealing with the aether theory.  Therefore, a null result of MM does scientifically contradict the aether hypothesis. 

Since its a matter of definitions here, no amount of arguing is going to win this one for you.

On the other hand, the question of preferred reference frames is interesting, particularly of co-moving coordinates.  Of course these ideas don't have much to do with the definition of aether.
 

Offline Phractality

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Re: Why no Æther
« Reply #27 on: 04/01/2012 17:45:13 »
I can't see what's so scientific about claiming something doesn't exist on the basis that it can't be detected. If nothing could travel faster than the speed of sound because all the forces between atoms acted at the speed of sound, accelerating something up towards the speed of sound would automatically slow down any kind of clock you tried to devise and contract things in the direction of travel, and if it was also impossible to detect the air directly, you'd have the same kind of situation in which many scientists would step beyond their competence and declare that the air does not exist, all based on an experiment (Michelson-Morley) which fails because the equipment is contracted by its own motion through the medium it's trying to detect. Claiming that that aether doesn't exist on the basis of MM is philosophy, not science.
Well, at least the newbie is on my side. Thanks for your support, David.

Again, this is an argument that amounts to moving the goalposts by redefining aether.  The aether theory assumes the speed of light isn't constant and therefore time dilation and length contraction don't exist.  If you redefine things so they both exist from the start, then you're not dealing with the aether theory.  Therefore, a null result of MM does scientifically contradict the aether hypothesis. 
It is true that SOME aether theories deny the constancy of the speed of light in all directions, and those particular aether theories were falsified by MM. Those theories are based on flawed aether models or flawed understanding of aether models.
Some modern aether models (at least my own) make it evident WHY the speed of light must be the same in all directions in all reference frames, despite propagating in a substantive medium.
Since its a matter of definitions here, no amount of arguing is going to win this one for you.
You're the one changing the definition of aether, here, claiming that a substantive medium cannot propagate light the same in all directions. Aether never was DEFINED as requiring light to propagate at different speeds in different directions. By definition, aether is just the medium for the propagation of light. That definition is not changed by denying that the medium is substantive. Advocates of aether models are saying that the medium IS substantive, and that doesn't change the definition, either. Substantive or not, the medium for propagation of light is aether. (And Santa Clause exists, whether or not he is a real person.)
On the other hand, the question of preferred reference frames is interesting, particularly of co-moving coordinates.  Of course these ideas don't have much to do with the definition of aether.
No, but they may have something to do with the detection of aether. Detecting a preferred reference frame is evidence for the immobility of aether. Aether's apparent lack immobility is what persuaded Einstein to reluctantly accept that aether is not substantive.
 

Offline David Cooper

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Re: Why no Æther
« Reply #28 on: 04/01/2012 19:48:50 »
Again, this is an argument that amounts to moving the goalposts by redefining aether.  The aether theory assumes the speed of light isn't constant and therefore time dilation and length contraction don't exist.  If you redefine things so they both exist from the start, then you're not dealing with the aether theory.  Therefore, a null result of MM does scientifically contradict the aether hypothesis.

I haven't heard before this bit about the aether theory assuming the speed of light isn't constant, but then I've probably just made assumptions about what the aether theory was, based on what it most obviously should have been. I always assumed it proposed a medium through which light travelled at a constant speed, but that you might be able to measure its speed as having different values if you are travelling relative to it as the apparent speed of light should be slower when it's travelling the same way you are going and faster when coming at you head on, just like with the speed of sound - you could therefore easily imagine that you would be able to measure the speed of light as changing, although that's still based on the central idea that the speed of light is fundamentally constant. What the MM experiment then showed was that you can't actually measure light as having different apparent speeds because it so happens that travelling relative to the proposed aether contracts your measuring equipment, slows down aparent time and has all manner of other effects which similarly conspire to wipe out any possibility of measuring a difference of any kind (ignoring quantum effects which may resolve the issue some day), so it turned out that there is no detectable difference in the apparent speed of light across your measuring equipment, even though there may still be a radical difference in the amount of time taken for light to cross the equipment in one direction as compared with the amount of time taken for it to go the other way. We can never measure time properly because we always require something to do a round trip between two ticks of a clock (even with a water clock or hour glass - you have to think about forces between particles acting in both directions), so we are incapable of detecting the difference in what ought to be the aparent speed of light if it could only be made aparent.

So, MM most certainly failed to disprove the most obvious aether theory. If they were actually testing some other kind of aether theory, then that would resolve one mystery (the mystery of why people keep claiming MM proved there is no aether), but it would also pose a bigger mystery: why weren't they testing a more rational aether theory? Had they really not thought it up? Or have you got it wrong? Was the aether theory they were testing the same rational one I have just outlined? If so, what was actually proved was this: you can't detect your movement relative to the proposed aether because your equipment is controlled by forces which travel at the speed of light - this is quite different from effects which allow you to measure changes in the speed of sound where your measuring equipment is governed by forces which act far faster than the speed of sound. It was a surprising result, though it could have been predicted by a mathematician in advance if one had happened to think his way down the right route in advance. MM showed up a flaw in the theory in that they wrongly thought they'd be able to measure differences which it turned out were beyond them, but it showed up no flaw in the core of the aether theory itself.
 

Offline David Cooper

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Re: Why no Æther
« Reply #29 on: 04/01/2012 19:58:25 »
Maybe I've just made another assumption - that no mathematician had predicted that moving through the aether would shorten the equipment and slow down its apparent time. Maybe someone had, in which case the only aether theories being tested would be the crazy ones which stubbornly stuck with the idea that differences would show up even though it had been shown mathematically that they wouldn't.

I don't think my assumption can be wrong though, because from everything I've read, the MM result came as a complete surprise to everyone, including the people doing the experiment.
 

Offline JP

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Re: Why no Æther
« Reply #30 on: 04/01/2012 23:44:20 »
Aether means light is like sound in that it has a constant speed in stationary aether, but it doesn't have a constant speed to all observers.  As you point out, if aether exists you can measure the speed of light being fast or slow.  The aether theory just includes galilean relativity, and has Lorentz transformations, so nothing is length contracted or time dilated.

The MM experiment shows it isn't measured fast or slow.  Therefore, the aether theory can't hold. 

If I'm following you right, you're arguing that you can keep the idea of "stuff" through which light propagates, but introduce Lorentz transformations to keep that stuff stationary with respect to every observer (so that the speed of light stays constant).  Isn't that mathematically identical to special relativity, not experimentally testable and overly complicated?  I'm going to post this question in New Theories, so we can have a better discussion of it.

Here's the new theories post on this topic: http://www.thenakedscientists.com/forum/index.php?topic=42695.new#new
« Last Edit: 04/01/2012 23:52:07 by JP »
 

Offline syhprum

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Re: Why no Æther
« Reply #31 on: 05/01/2012 16:07:47 »
I meant to be a little provocative when I mentioned the the dreaded five and  a half letter word but am rather surprised what strange paths we have been drawn down.
 

Offline burning

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Re: Why no Æther
« Reply #32 on: 05/01/2012 16:20:24 »
The last few posts have nicely recapitulated what the physics community went through in the wake of the MM experiment.  There were various attempts to "save" the aether by positing various mechanical properties of the aether that would explain the MM null result.  The problem was that these hypotheses didn't end up leading anywhere.  If they made predictions, the predictions didn't pan out, and you then had to posit something else to explain that failure.  Physics was left with the problem that if there was an aether, it was apparently unstudiable.

On the other hand, eventually you had relativity.  It rejected or at least ignored the aether hypothesis, and from a very lean set of assumptions was able to make a large set of predictions that, one by one, turned out to be accurate.  Against the advantages of relativity, the aether theories could offer the advantage that... they included an aether.  At that point I think the question from the OP needs to be reversed, and we need to ask "Why an aether?"

Now I agree that if by aether we mean "a medium required to support the propogation of electromagnetic waves," then, no, we can't say that science has disproved the existence of such a medium.  However, JP is completely correct that science has disproved the existence of an aether that in any way resembles what everyone from J. C. Maxell to A. A. Michelson was expecting and hoping for.

So from the fact that, as far as we can tell today, there is no studiable aether, do you conclude that there is no aether at all, or do you conclude that, despite its predictive power, relativity is metaphysically flawed and that there really is an aether.  The first choice has been dismissed in this thread as philosophy rather than science, but I can't see that the second choice can claim any different.

Now I don't actually think it is bad to select the second choice, if you are rigorous and intellectually honest about it.  It is a metaphysical preference that, at this time, does not have any objective support.  I think it could be very useful for some researchers to pursue trying to develop an aether theory, but anyone who does needs to understand what they would need to do to convince the greater physics community that their result is worth paying attention to.  It is going to need to reproduce the successful predictions of relativity while also doing at least one of two other things.  First, it could do so from a comparably streamlined set of assumptions to those of relativity.  If that's all it does, it will never be a replacement, but it would reasonably be considered a rival interpretation.  Second, it could provide a new set of predictions that could be tested.  Anything that provides neither is not going to be scientifically useful, and the existence of an aether would remain metaphysics.
 

Offline simplified

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Re: Why no Æther
« Reply #33 on: 05/01/2012 16:51:14 »
Gravitational ether exists,but it creates "space-time".
 

Offline David Cooper

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Re: Why no Æther
« Reply #34 on: 05/01/2012 21:01:02 »
Aether means light is like sound in that it has a constant speed in stationary aether, but it doesn't have a constant speed to all observers.

In what way does it make sense to say that it ceases to be aether once you've realised that the second part of that isn't going to pan out? You initially expect that it won't have a constant speed to all observers because you haven't thought it through fully, but when you eventually think through the maths of it in detail you realise that it won't actually be possible to detect those variations at all. Realising that you aren't going to be able to detect the aether so easily doesn't change the bit about light having a constant speed in stationary aether, so it makes no sense ban it from being called aether - the only thing that has changed is that you have discovered a barrier which gets in the way of identifying it.

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As you point out, if aether exists you can measure the speed of light being fast or slow.

I said you might expect that you could measure the speed of light being fast or slow, but you'd then discover you were wrong and realise why when you think it through in detail - it isn't like the speed of sound where you can use clocks governed by the speed of light to show up the difference. To show up the difference with in speed relative to the aether you'd need clocks governed by forces which act faster than the speed of light, and it isn't easy to find such clocks.

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The aether theory just includes galilean relativity, and has Lorentz transformations, so nothing is length contracted or time dilated.

I thought Lorentz transformations were precisely about contracting lengths.

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The MM experiment shows it isn't measured fast or slow.  Therefore, the aether theory can't hold.

It shows nothing of the kind - it shows that there is an unexpected problem. When you start to think about it properly, suddenly it all makes sense, and it does so without destroying the aether theory. You imagine a space ship travelling at a substantial percentage of the speed of light and with a lamp in the middle of it. The light has much further to go to reach the front of the ship because the front of the ship is racing away from it, whereas the back wall is hurtling towards the lamp. This makes you think that the wall at the front end should be much darker than normal as the light will have had more time to spread out before hitting it, while the back wall will be much brighter than normal. But that won't happen - the lamp pushes more light forwards and less backwards, resulting in the front and back walls being equally bright. Why should this happen? Well, imagine a camera with a 50mm lens on it. Put it next to the lamp and point it towards the front wall. The light coming from the wall reaches the camera far sooner than it would if the ship wasn't moving, but the lens will also behave as if it's closer to the focal plane for the same reason, so it acts like a wide-angle lens and compensates exactly for the differences caused by the speed of travel. If you point the camera towards the back wall the opposite happens - the lens behaves like a strong telephoto, the light having to go much further after passing through the lens before it reaches the film plane. The shapes of the lenses also behave differently, ensuring that perfect focus is maintained. If you try to cheat the system by using a mirror to tap light that sets out backwards from the lamp to redirect it forwards in the hope that you can get it to send less light forwards than should be allowed, lo and behold the flat mirror behaves as if it's curved and it concentrates the light forwards. These simple optical effects illustrate how forces would likewise be concentrated increasingly forwards as an object moves faster, maintaining the normal balance with the side effect that objects have to sit closer together in the direction of travel. The slowing of time is then fully accounted for by the total distance that things have to travel at the speed of light to complete a round trip. All of this is fully compatible with the idea of aether.

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If I'm following you right, you're arguing that you can keep the idea of "stuff" through which light propagates, but introduce Lorentz transformations to keep that stuff stationary with respect to every observer (so that the speed of light stays constant).  Isn't that mathematically identical to special relativity, not experimentally testable and overly complicated?

I expect the two theories are mathematically identical. The question is, how is it less complicated to chuck the idea of an aether and then to rely on not just one aether to maintain the distances between things, but an aether for every possible frame of reference, all hidden under the simple description "spacetime"? Einstein admitted that there has to be some kind of aether to create separation between things - if they are sitting in absolute nothing, there can be no separation because there's nothing to maintain the spacings. With a single aether, it's relatively easy to do the job. With spacetime, you aren't allowed to have a single aether in a preferred frame of reference, so spacetime has to do something infinitely more complex, namely having a different aether for each frame, and that idea sounds so ridiculous that you then have to brush the idea of aether under the carpet and fool yourself into thinking you don't need one at all, backed by the fact it isn't actually necessary in the maths, regardless of whether it's necessary in actuality (but we can farm that off into philosophy and forget about it). I've always regarded Einstein's relativity as an overly-complex aether theory.
 

Offline David Cooper

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Re: Why no Æther
« Reply #35 on: 05/01/2012 21:22:35 »
So from the fact that, as far as we can tell today, there is no studiable aether, do you conclude that there is no aether at all, or do you conclude that, despite its predictive power, relativity is metaphysically flawed and that there really is an aether.  The first choice has been dismissed in this thread as philosophy rather than science, but I can't see that the second choice can claim any different.

Both can be dismissed as philosophy, as can anything in science which can't be proven by experiment. MM didn't disprove the idea of aether at all - claims that it did are both bad science and bad philosophy. Claims that it currently can't be detected may be good science (unless QM really has demonstrated faster than light phenomena, although even then it may not allow a preferred frame to be pinned down). Claiming that there must be an aether would be bad science unless there was a test that could be done to prove it, but it might not be bad philosophy to make such a claim, just as claiming that there is no need for an aether might not be bad philosophy either - that's an argument for elsewhere. What matters here is that MM didn't prove that there is no aether, and it's a pity that so many physics books say that it does, because a lot of people take everything they read in them as gospel. I'm not accusing anyone here of that - this looks as if it's the most rational group of people I've ever found on the Net.
« Last Edit: 05/01/2012 21:26:13 by David Cooper »
 

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Re: Why no Æther
« Reply #35 on: 05/01/2012 21:22:35 »

 

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