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Merged Does CERN prove Einstein wrong?

According to my arithmetic, the difference in arrival times of the two signals is about 30 femtoseconds. You'll need measuring equipment capable of measuring to a precision significantly better than 30fs, and you'll have to time the pulses to a similar level of precision despite the fact that one laser is moving at 100ms-1 relative to the other.
Dave

"Optical autocorrelators are used for various purposes, in particular for the measurement of the duration of ultrashort pulses with picosecond or femtosecond durations, where an electronic apparatus (based on, e.g., a photodiode) would be too slow." -- http://www.rp-photonics.com/autocorrelators.html

"Titanium–sapphire lasers, often Kerr lens mode-locked, can generate the shortest pulses with durations down to approximately 5 fs." -- http://www.rp-photonics.com/ultrafast_lasers.html
 
"Optical autocorrelators are used for various purposes, in particular for the measurement of the duration of ultrashort pulses with picosecond or femtosecond durations, where an electronic apparatus (based on, e.g., a photodiode) would be too slow." -- http://www.rp-photonics.com/autocorrelators.html

"Titanium–sapphire lasers, often Kerr lens mode-locked, can generate the shortest pulses with durations down to approximately 5 fs." -- http://www.rp-photonics.com/ultrafast_lasers.html

Thank you for showing that you can look up random facts on the internet and cut and paste them correctly. Of course, being able to generate pulses with a short duration, and to measure the duration of the pulse, is more or less irrelevant to the problems of synchronising, to better than 30fs, the time of generation of pulses in two different lasers of which one is moving at 100ms^-1 with respect to the other, or of measuring the difference between the times of arrival of those pulses at two different photodetectors, neither of which is able to resolve a time interval that short; but at least you're able to recognise words that, in a different context, might have been relevant.

Dave
 
Another cool experiment would be to have a laser moving in a long tube with electromagnets. The laser is accelerated to a very high speed of 1000 m/s or something like that. And the laser is set to emit short pulses at a fixed time interval (some fraction of a second). At the end of the tube a photon detector registers the pulses from the laser.

Ball and magnets: http://www.youtube.com/watch?v=kcuCt_kAD2k
 
Another cool experiment would be to have a laser moving in a long tube with electromagnets. The laser is accelerated to a very high speed of 1000 m/s or something like that. And the laser is set to emit short pulses at a fixed time interval (some fraction of a second). At the end of the tube a photon detector registers the pulses from the laser.

Ball and magnets: http://www.youtube.com/watch?v=kcuCt_kAD2k

Here's a better experiment. Take a laser that's moving at 30,000 m/s, and split the beam so that part of it moves parallel to the laser's movement, and the other part perpendicular to it. Then see if you can measure any difference in speed between the two beams.

Dave
 
Here's a better experiment. Take a laser that's moving at 30,000 m/s, and split the beam so that part of it moves parallel to the laser's movement, and the other part perpendicular to it. Then see if you can measure any difference in speed between the two beams.

Dave

That sounds much more complicated. How to reach 30,000 m/s? And how to practically do the measurements?

The tube experiment is very simple, even in practice. And the measurement is simple. Just compare the pulse rate from the laser to the pulse rate detected at the photon detector. If the pulse rate from the laser is say 100 pulses per second, then the pulse rate at the detector should also be 100 pulses per second, even when the laser has accelerated to 1000 m/s, if Einstein's relativity is correct.
 
That sounds much more complicated. How to reach 30,000 m/s? And how to practically do the measurements?

The tube experiment is very simple, even in practice. And the measurement is simple. Just compare the pulse rate from the laser to the pulse rate detected at the photon detector. If the pulse rate from the laser is say 100 pulses per second, then the pulse rate at the detector should also be 100 pulses per second, even when the laser has accelerated to 1000 m/s, if Einstein's relativity is correct.

Just remember that you're standing on a planet that's evolving
And revolving at nine hundred miles an hour
Orbiting at eighteen miles a second, so it's reckoned,
A sun which is the source of all our power.
The Sun, and you and me, and all the stars that we can see
Are traveling a million miles a day
At forty thousand miles an hour, through an outer spiral arm
Of the galaxy we call the Milky Way.

...

So, if you're feeling small and insignificant, remember
How amazingly unlikely was your birth.
And pray that there's intelligent life somewhere out in space
'cause there's bugger-all here on Earth.
 
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Just remember that you're standing on a planet that's evolving
And revolving at nine hundred miles an hour
Orbiting at eighteen miles a second, so it's reckoned,
A sun which is the source of all our power.
The Sun, and you and me, and all the stars that we can see
Are traveling a million miles a day
At forty thousand miles an hour, through an outer spiral arm
Of the galaxy we call the Milky Way.

Joking aside, the measurement is relative to the observer who is the detector. So the frame of reference is the laser moving at 1000 m/s. That's all that's needed.
 
You're standing on it, and it's been done. In fact, it was done for the first time over a hundred years ago (although not with a laser; it turns out it doesn't need one).

Dave

Ah! You mean this:

"Michelson-Morley Experiments Revisited and the Cosmic Background Radiation Preferred Frame

The re-analysis here of the Michelson-Morley experimental data, correcting for the refractive index effect of the air, reveals an absolute speed of the Earth of v=359+/-54 km/s, which is in excellent agreement with the speed of v=365+/-18 km/s determined from the dipole fit, in 1991, to the NASA COBE satellite Cosmic Background Radiation (CBR) observations. Other experiments where the interferometers operated in air (Miller 1925,1933) or helium (Illingworth 1927) give similar results when re-analysed. These experimental results refute Einstein's assertion that absolute motion through space has no meaning. ..." [emphasis added :D] -- http://arxiv.org/abs/physics/0205065
 
Ah! You mean this:

"Michelson-Morley Experiments Revisited and the Cosmic Background Radiation Preferred Frame

Yes, I mean an experiment whose significance is agreed by all except a small minority of scientists, whose work you nevertheless feel should be elevated to a higher standard of significance than it possesses merely because it is a minority view, and for some reason you want to experience the feeling of superiority resulting from the belief that the rest of the world is wrong and you are right. Of course, as everyone reading this thread knows, you are not trumpeting Cahill's work because of any capacity on your part to understand it - you've demonstrated your inability to grasp the simplest relevant concepts many times over - but because it agrees with your prejudices.

Now, I see that Cahill's entire analysis stems from the following statement:

In reviewing the operation of the Michelson-Morley interferometer (see below) it was noticed that the Fitzgerald-Lorentz contraction explanation only implies a null effect if the experiment is performed in vacuum. In air, in which photons travel slightly slower than in vacuum, there should be a small fringe shift effect when the apparatus is rotated, even after taking account of the Fitzgerald-Lorentz contraction.

This is, as far as I can see, an irrelevant comment. If we start from the postulate that there is no such thing as absolute motion, we therefore arrive very simply at the conclusion that the Michelson-Morley experiment gives a null result whatever the medium in which it is performed, provided only that there is no motion of the dielectric medium relative to the apparatus. The Fitzgerald-Lorentz contraction is then derived as a consequence of this observation, rather than being treated in isolation as an anomalous effect. Since this incorrect claim - that the Michelson-Morley experiment should not have yielded a null result - is the foundation of Cahill's further calculations, there is no need to give them any consideration beyond this point. No doubt this was equally obvious to the peer reviewers who rejected this work for publication in Nature.

Dave​
 
Yes, I mean an experiment whose significance is agreed by all except a small minority of scientists, whose work you nevertheless feel should be elevated to a higher standard of significance than it possesses merely because it is a minority view, and for some reason you want to experience the feeling of superiority resulting from the belief that the rest of the world is wrong and you are right. Of course, as everyone reading this thread knows, you are not trumpeting Cahill's work because of any capacity on your part to understand it - you've demonstrated your inability to grasp the simplest relevant concepts many times over - but because it agrees with your prejudices.

Now, I see that Cahill's entire analysis stems from the following statement:



This is, as far as I can see, an irrelevant comment. If we start from the postulate that there is no such thing as absolute motion, we therefore arrive very simply at the conclusion that the Michelson-Morley experiment gives a null result whatever the medium in which it is performed, provided only that there is no motion of the dielectric medium relative to the apparatus. The Fitzgerald-Lorentz contraction is then derived as a consequence of this observation, rather than being treated in isolation as an anomalous effect. Since this incorrect claim - that the Michelson-Morley experiment should not have yielded a null result - is the foundation of Cahill's further calculations, there is no need to give them any consideration beyond this point. No doubt this was equally obvious to the peer reviewers who rejected this work for publication in Nature.

Dave​

Ok, but does it really test the claim that the speed of light cannot be exceeded? That's what the experiments I proposed test, such as the claim that c + 1000 m/s = c. And that's what I'm interested in finding out.
 
Ok, but does it really test the claim that the speed of light cannot be exceeded? That's what the experiments I proposed test, such as the claim that c + 1000 m/s = c. And that's what I'm interested in finding out.
Really? Somehow I don't believe you're actually interested in finding anything out.
 
Really? Somehow I don't believe you're actually interested in finding anything out.

The moving laser in a tube experiment would be cool to test. Hmm... There must be some similar experiments already done. Maybe not. :eek: I found:

"The aspect of the principle that defies common sense and logical reasoning is light speed invariance relative to a moving observer. ... We note that there is no experiment that directly verifies this aspect of the principle even though many textbooks imply otherwise." -- http://webcache.googleusercontent.c...elec/staff/sgift/special_relativity.pdf&hl=en
 
Another cool experiment would be to have a laser moving in a long tube with electromagnets. The laser is accelerated to a very high speed of 1000 m/s or something like that. And the laser is set to emit short pulses at a fixed time interval (some fraction of a second). At the end of the tube a photon detector registers the pulses from the laser.

Ball and magnets: http://www.youtube.com/watch?v=kcuCt_kAD2k

Do you believe in a stationary Earth?

Why all this bothering about with lasers on rails, when you are on a platform that is moving at 100,000 KPH just in the solar orbit alone. The entire solar system is moving at close to that velocity towards Vega, for instance.
 
Do you believe in a stationary Earth?

Why all this bothering about with lasers on rails, when you are on a platform that is moving at 100,000 KPH just in the solar orbit alone. The entire solar system is moving at close to that velocity towards Vega, for instance.

You mean for example measure light from stars? But how to measure the velocity of light from a star? The redshift for example could be caused by vacuum energy friction: http://www.newscientist.com/article/mg20927994.100-vacuum-has-friction-after-all.html

I think it's safer to use an experiment here on Earth to measure the speed of for example c + 1000 m/s = c.
 
Of course Anders won't accept this because of the lunar lunacy, but we have a mirror on the moon, and can measure the speed of light by reflecting a laser off of it and timing the time to get a reflection. Surely even Anders will admit that the earth and moon are moving relative to each other, yet the measurement is still c, same as if you put a mirror and laser on the surface on the earth.
 
Thank you for showing that you can look up random facts on the internet and cut and paste them correctly. Of course, being able to generate pulses with a short duration, and to measure the duration of the pulse, is more or less irrelevant to the problems of synchronising, to better than 30fs, the time of generation of pulses in two different lasers of which one is moving at 100ms^-1 with respect to the other, or of measuring the difference between the times of arrival of those pulses at two different photodetectors, neither of which is able to resolve a time interval that short; but at least you're able to recognise words that, in a different context, might have been relevant.

Dave

My brain is dealing with page layouts right now and I can't remember my physics...I was wondering if there might be some trick you could do with interference patterns that would be easier to do in a modest lab, but am I correct in remembering that phase velocity is allowed to exceed the speed of light, and would that not be a problem?
 
Of course Anders won't accept this because of the lunar lunacy, but we have a mirror on the moon, and can measure the speed of light by reflecting a laser off of it and timing the time to get a reflection. Surely even Anders will admit that the earth and moon are moving relative to each other, yet the measurement is still c, same as if you put a mirror and laser on the surface on the earth.

I found an article that showed how students who reflected a laser against that supposed mirror found that the reflection was an order of magnitude too weak! My guess is that there is no such mirror and that that's only a bright spot on the moon surface that NASA has located and chosen to be the 'mirror'.

Besides, isn't the relative velocity between Earth and the moon very small?
 
Of course Anders won't accept this because of the lunar lunacy, but we have a mirror on the moon, and can measure the speed of light by reflecting a laser off of it and timing the time to get a reflection. Surely even Anders will admit that the earth and moon are moving relative to each other, yet the measurement is still c, same as if you put a mirror and laser on the surface on the earth.

You fool, that laser is used only to target ICBMS (according to a different thread!)

Unfortunately the relative movement there is fairly low.
 

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