Discussion:
Post-Truth (Post-Sanity) Education: Einstein's Time Travel
(trop ancien pour répondre)
Pentcho Valev
2018-11-26 11:42:20 UTC
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Brian Greene: "Time travel is absolutely possible. And this is not some sort of weird sci-fi thing that I'm talking about here. Albert Einstein taught us more than 100 years ago that time travel is possible if you're focusing upon time travel to the future. And I'm not referring to the silly thing that we all age, right. We're all going into the future. Sure, I'm talking about if you wanted to leapfrog into the future, if you wanted to see what the Earth will be like a million years from now, Albert Einstein told us how to do that. In fact he told us two ways of how to do it. You can build a spaceship, go out into space near the speed of light, turn around and come back. Imagine you go out for six months and you turn around and you come back for six months. You will be one year older. But he taught us that your time is elapsing much slower than time back on Earth. So when you step out of your ship you're one year older but Earth has gone through many, many years. It can have gone through 10,000, 100,000 or a million years depending on how close to the speed of light you traveled."


Time travel to the future is only possible if Einstein's 1905 conclusion

"the clock moved from A to B lags behind the other which has remained at B" http://www.fourmilab.ch/etexts/einstein/specrel/www/

is true. The conclusion is non sequitur - it doesn't follow VALIDLY from Einstein's 1905 postulates. This means that, even if the postulates were true (actually the second one is false), the conclusion remains unjustified.

The following two conclusions VALIDLY follow from the postulates:

Conclusion 1: The clock moved from A to B lags behind the other which has remained at B, as judged from the stationary system.

Conclusion 2: The clock which has remained at B lags behind the clock moved from A to B, as judged from the moving system.

Conclusions 1 and 2, in their combination, give no prediction for the readings of the two clocks as they meet at B. That is, although conclusions 1 and 2 are logically correct (do follow from the postulates), their combination amounts to nonsense.

In contrast, Einstein's INVALIDLY deduced conclusion

"the clock moved from A to B lags behind the other which has remained at B"

provides a straightforward prediction: The moving clock is slow and accordingly its (moving) owner can remain virtually unchanged while sixty million years are passing for the stationary system (travel into the future par excellence):

Thibault Damour: "The paradigm of the special relativistic upheaval of the usual concept of time is the twin paradox. Let us emphasize that this striking example of time dilation proves that time travel (towards the future) is possible. As a gedanken experiment (if we neglect practicalities such as the technology needed for reaching velocities comparable to the velocity of light, the cost of the fuel and the capacity of the traveller to sustain high accelerations), it shows that a sentient being can jump, "within a minute" (of his experienced time) arbitrarily far in the future, say sixty million years ahead, and see, and be part of, what (will) happen then on Earth. This is a clear way of realizing that the future "already exists" (as we can experience it "in a minute")." http://www.bourbaphy.fr/damourtemps.pdf

Pentcho Valev
Pentcho Valev
2018-11-26 17:30:39 UTC
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The time-travel idiocy does not follow VALIDLY from Einstein's 1905 postulates but the barn-pole idiocy does. Einstein's false constant-speed-of-light postulate entails that unlimitedly long objects can gloriously be trapped, "in a compressed state", inside unlimitedly short containers:

"These are the props. You own a barn, 40m long, with automatic doors at either end, that can be opened and closed simultaneously by a switch. You also have a pole, 80m long, which of course won't fit in the barn. [...] So, as the pole passes through the barn, there is an instant when it is completely within the barn. At that instant, you close both doors simultaneously, with your switch. [...] If it does not explode under the strain and it is sufficiently elastic it will come to rest and start to spring back to its natural shape but since it is too big for the barn the other end is now going to crash into the back door and the rod will be trapped in a compressed state inside the barn." http://math.ucr.edu/home/baez/physics/Relativity/SR/barn_pole.html

"If it does not explode..." - can it explode? Yes, the effect can be called "Einstein explosion" - it can only occur in Einstein's schizophrenic world:

"In a more complicated version of the paradox, we can physically trap the ladder once it is fully inside the garage. This could be done, for instance, by not opening the exit door again after we close it. In the frame of the garage, we assume the exit door is immovable, and so when the ladder hits it, we say that it instantaneously stops. By this time, the entrance door has also closed, and so the ladder is stuck inside the garage. As its relative velocity is now zero, it is not length contracted, and is now longer than the garage; it will have to bend, snap, or explode." https://en.wikipedia.org/wiki/Ladder_paradox

Pentcho Valev
Pentcho Valev
2018-11-27 08:42:46 UTC
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Post-sanity (Einsteinian) science:

"I'm Brian Greene, professor of physics and mathematics at Columbia University and co-founder of the World Science Festival. It's critical that you realize that there are two types of time travel, and they are radically different. Time travel to the future? Definitely possible. We know how to do it because Einstein showed us the way over a hundred years ago. It’s surprising how few people actually really know about this in their bones. He showed that if you go out into space and travel near the speed of light, and you turn around, and you come back, your clock will be ticking off time more slowly. So, when you step off it's going to be the future on planet Earth. You will have time traveled into the future." http://www.businessinsider.com/how-to-time-travel-with-wormholes-2017-11

Lisa Randall, Michio Kaku, Brian Cox, Neil deGrasse Tyson, Brian Greene: "Now, listen carefully. The faster you move, the heavier you get. Light travels at the same speed no matter how you look at it. No matter how I move relative to you light travels at the same speed. No matter who is doing the measurement and no matter what direction you are moving the speed of light is the same. The speed of light is the same no matter what direction or how fast... As you travel faster time slows down. Everything slows down. Everything slows down. Time slows down when you move. Time passes at a different rate. Clocks run slow. It's a monumental shift in how we see the world. It's a beautiful piece of science. It's a beautifully elegant theory. It's a beautiful piece of science. It's a beautiful piece..."


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