Physicist Sean Carroll on time travel (1:06:03)
I recommend you watch the whole video - it's very interesting.
See if you can spot any errors.
When Carroll talked about a party on Alpha Centauri
I'm sure he meant to say "a party on a planet orbiting Alpha Centauri."
I think we can give him a break on that one.
But the more serious disagreement I have with his lecture is this:
Beginning after the 29-minute mark and lasting for about 15 minutes,
Carroll explains Einstein's theory.
He presents a diagram showing someone entering a black hole,
following the curved path of his light cone,
and then meeting up with his past self (the one who entered the black hole).
The problem with this theory is that,
if you meetup with your past self,
then the atoms that make you "you"
would have to be in two places at the same time.
The laws of physics do not allow atoms to have this property.
In Carroll's imaginary scenario, whatever you are looking at - it cannot be you.
It may be something that looks like you ... but it cannot be you.
The argument that even if you aren't the same person,
you still could have traveled back in time also fails
because to do so would require that every particle in the Universe
be in exactly the same position as it was at the time you entered the black hole,
and obviously, that is impossible because then he would have to explain
how he would return every photon in the universe back to where it used to be.
(I was tempted to put this story in "pseudoscience")
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