2017-11-17 17:59:08 UTC
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
Neil deGrasse Tyson: "One of the towering great achievements of the human mind in our understanding of the universe is Einstein's theories of relativity. [...] It makes only two assumptions: that the speed of light in a vacuum is constant no matter who is doing the measurement and no matter in what direction you are moving or how fast. You always get the same measurement for the speed of light. That's Assumption 1 which by the way the experiment has shown to be true. [...] Given those two tenets, extraordinary spooky phenomena derive from them. For example: As you travel faster [...] time ticks more slowly for you than it does for other people who are not."
That the traveling twin returns younger, per se, is an idiocy of course but there is something much more idiotic in the story: The youthfulness of the traveling twin does not follow from the two assumptions (Einstein's 1905 postulates). That is, the assumptions, true or false, logically entail some conclusions, but "the traveling twin returns younger" is not one of them.
Tyson is lying when he says
"As you travel faster [...] time ticks MORE SLOWLY for you than it does for other people who are not."
Actually, special relativity says the opposite:
As you travel faster, time ticks FASTER for you than it does for other people who are not.
Here are Einsteinians who, unlike Neil deGrasse Tyson, are telling the truth:
David Morin, Introduction to Classical Mechanics With Problems and Solutions, Chapter 11, p. 14: "Twin A stays on the earth, while twin B flies quickly to a distant star and back. [...] For the entire outward and return parts of the trip, B does observe A's clock running slow..." http://www.people.fas.harvard.edu/~djmorin/chap11.pdf
"The situation is that a man sets off in a rocket travelling at high speed away from Earth, whilst his twin brother stays on Earth. [...] ...the twin in the spaceship considers himself to be the stationary twin, and therefore as he looks back towards Earth he sees his brother ageing more slowly than himself." http://topquark.hubpages.com/hub/Twin-Paradox
So the correct prediction of special relativity (one that validly follows from the postulates) is that, when he returns, the traveling twin will see his (stationary) brother younger than himself. Another correct prediction is that the stationary twin will see his (traveling) brother younger than himself. The absurdity is obvious.
How can Einstein's relativity be saved? Some additional absurdity has to be introduced, able to neutralize the original one. In 1918 Einstein admitted that special relativity is contradictory and turned to general relativity - he informed the gullible world that, during the turning-around acceleration of the traveling twin, a HOMOGENEOUS gravitational field appears which is responsible for a quick, almost instantaneous, ageing of the distant stationary twin:
Albert Einstein 1918: "A homogeneous gravitational field appears..." http://sciliterature.50webs.com/Dialog.htm
David Morin (quoted above) perhaps finds Einstein's HOMOGENEOUS gravitational field too idiotic but introduces it nevertheless - he calls it "enough strangeness" - words that perhaps sound less idiotic to him:
David Morin: "Twin A stays on the earth, while twin B flies quickly to a distant star and back. [...] For the entire outward and return parts of the trip, B does observe A's clock running slow, but enough strangeness occurs during the turning-around period to make A end up older."