Over a century ago, Einstein wrote his theories of special relativity and general relativity. Within those theories, he predicted that, as an object moves faster, it slightly contracts in length. However, 50 years later Penrose and Terrell predicted that what one would see is instead that the object is rotated. In a recent experiment, physicists proved that this Penrose-Terrell effect is actually real. Let’s take a look.She is a big Einstein idolizer. Her favorite prop is an Einstein bobblehead.
Let me review the basic facts.
The relativity length contraction was discovered by Fitzgerald in 1889 and Lorentz in 1892. Lorentz also discovered time dilation in 1895. Both of them used these to explain the 1887 Michelson-Morley experiment.
Poincare in 1905 and Minkowski in 1907 explained these as a new geometry of spacetime. In their interpretation, the spacetime distortions are not real, but an artifact of choosing a frame in the 4D non-euclidean geometry. This interpretation was quickly accepted, and is the dominant one today.
Dr. Bee starts:
0:00 Albert Einstein totally changed our understanding of space and time. ...No, Lorentz and others made those remarkable predictions 10+ years ahead of Einstein. They said that the motion actually actually made the Michelson apparatus shorter. I think most physicists today would say that it only appears shorter.Einstein’s theory of 0:46 special relativity makes two most remarkable predictions. The first is time dilation, 0:52 the other one is length contraction. Time dilation means that if an object moves faster 0:58 than its internal time passes slower. Length contraction means that the same fast-moving 1:05 object will also be shorter. It’s not that it appears shorter, it actually is shorter.
In 1931, a group of scientists went so far 1:24 as to publish a book called “100 authors against Einstein.” It’s an interesting historical summary 1:31 of why people rejected Einstein’s insights, more than 2 decades after he had put them forward.Her opinion is very strange. Lorentz and Poincare had all the equations and predictions before Einstein. The only way to credit Einstein for relativity is to say that he had a superior philosophical construction. If the Lorentz contraction is real and the 1931 book was wrong to say that Einstein had a philosophical construction, then Lorentz had it all before Einstein.1:38 Some of them claimed Einstein’s maths is wrong. Some said the maths is right, 1:44 but they did it earlier.
The most frequent objection though was that they thought 1:49 Einstein’s theory is merely a philosophical construction. They thought that special 1:55 relativity tells us something about the way we see things. Not about how they really are. 2:01 Well, they were wrong. We know that length contraction is real. A moving object really is 2:08 shorter.
Here is what Poincare wrote in 1905, before Einstein:
But the question can still be seen form another point of view, which could be better understood by analogy. Let us suppose an astronomer before Copernicus who reflects on the system of Ptolemy; ...He says his view is like Copernicus rejecting Ptolemy, putting a new view on the same data. The relativity contraction is only apparent, due to our methods of measurement.Or this part which would be, so to speak, common to all the physical phenomena, would be only apparent, something which would be due to our methods of measurement. ...
so that the theory of Lorentz is as completely rejected as it was the system of Ptolemy by the intervention of Copernicus.
This is the modern view of relativity. It was popularized by Minkowski in 1907-8, and accepted ever since. Einstein is only credited because of a mistaken belief that he contributed to this modern view. In fact, the view was published before Einstein, and Einstein rejected it when he learned about it.
Most of Dr. Bee's video is about a new paper confirming a visual illusion that Penrose discovered.
Just a simple thought experiment to show that the ED- (and STR-) relativistic length contractions cannot be real:
ReplyDeleteTake two identical poles, P1 and P2. You know the rest of the story: Keep P1 on earth, send the other aboard a rocket, built by some alien civilization so that it really goes to (and maintains) a constant velocity of, say, gamma = 2 (w.r.t. the earth).
Fitzgerald and Lorentz said that P2 really contracts to half of P2's original length (when it was on the earth).
Then Poincare realized that to the alien, P2 maintained its length all the time, and P1's length had become half the original length.
Both contractions can't really occur in reality, at the same time, and so, the length contraction cannot be real; it can only be apparent.
All that has been a very well known story --- actually well worn out. But some insisted (and still do) that the relativistic length contractions and time dilations are real; that P2 really contracts to half its length. (A few years ago, I had read a tweet in which a well read guy had said that people carry this misconception (and that was the word he had used) that moving clocks don't really run slower, whereas, according to him, they actually do run slower.)
Hence the labour of writing this reply. Hope they all read this one (too).
Just take a third identical pole, P3; another alien rocket; the second rocket moves at constant velocity of gamma = 3 (w.r.t. the earth) at the same time.
They would say: Yes, so P3 contracts to 1/3rd its original length. Really.
OK. But what is the contraction of P2 that is seen by the alien in the *second* rocket (the one which carries P3)? Of course, it won't be 1/3rd, but the point is: It can't be 1/2 either.
If so, the question is: By what amount does P2 really, really(, really, ...) contract?
--Ajit
PS: The only ``loop-hole'' they might come up with:
No, they would say (to the rest of physicists): But you are comparing the reality of this observer with the reality of that observer. You aren't comparing realities of two objects to the same observer.
So, to them, reality (the identity of an object) is not independent of any and all observers. The very reality itself dances differently to the respective tunes of different observers.
They can't have any other escape.
And, if they are mathematically trained, too, then a good question to raise would be: Is LT invertible? In other words, can LT apply from two different (inertial) frames?
But I guess the time for raising such questions, too, has already run out. ... Sigh... Time doesn't dilate either.
The relativity length contraction was discovered by Fitzgerald in 1889 and Lorentz in 1992. Lorentz also discovered time dilation in 1995.
ReplyDeleteWow he did live a long life.
Thanks. Fixed.
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