On Aug 24, 6:19 pm, Rex wrote:
They say time is what the clock measures and time is something
that has already happened. But i've been continued puzzled about
what time really is. How come physicists explore the possibility of
time travel. How can you go back to the past when it has already
happened. In newtonian argument, it may be as plain as this. But
in light of SR and GR. Time seems to be something more and
has an almost magical quality to it. Can you describe time in
such a way that it can make time travel makes sense (theoretically
speaking)?


No I can't, but I think I can explain why such a concept arises.

Space is a relational concept. There is no absolute space, there are
only spatial relationships betwen objects.

When you get get to some "place" that seems to be some "place" that
you've been before - that's an illusion.

Let's say you visit Trafalgar square, which isn't really a "place" -
it's a collection of objects in certain spatial relationships with
respect to each other and the Earth and with the Sun.

"Return" to Trafalgar Square 6 months later and that "place" has moved
186 million miles wrt the Sun and the Sun has moved further still wrt
the Gakaxy. The Galaxy itself as moved..... ... and so on.

So you're not really in the same "place".

If you stay in the same "place" wrt the Sun, you'll find that the
Earth quickly leaves you behind.


Time is also a relational concept. There is no absolute time, there
are only temporal relationships amongst objects.

If you stay fixed at some time, you'll quickly find that the Earth has
left you behind.

These relational concepts are not well understood.

No rational person would think that if you went back to some "relative
location in space" (Trafalgar Square) the same people would be there
as were there on your last visit.

Yet those same otherwise rational persons think that if they go back
to some "relative location in time" that their grandfather would still
be there and they could kill him.

Love,
Jenny