Time Travel???

Yep. Think I've got it now. Malcolm's time will not have slowed down - that is his body will experience the same amount of time in his spaceship as it would have done on earth. But seen from earth, his spaceship, and all in it, will appear to be experiencing time slower than the observers on earth. Is that it?

Malcolm's elapsing of time appears slow in the scale of time of the viewer on the earth.

Axon, you are still missing the most interesting part.

When Malcolm returns to Earth and talks to Joshua again (i.e. they are now at the same place and are talking together). Malcolm will have experienced less time than Joshua. This, to them will be a very real and measurable difference.

Malcom will say 10 years have past (and he will be correct). He will be able to prove this with his watch, his body (which will have aged 10 years) and the things he has done -- as well as any other test you can think of to show many many years he has experienced.

At the same time Joshua will say 15 years have past ( and he also will be correct). Joshua will be able to prove this with *his* watch, his body (which will be 5 years older then Malcolms) and the things he has done.

In this case since they are together ... and talking together - you can;'t really say that 10 years "appears" to have gone by for Malcolm or for Joshua. It is more concrete than that. 10 years *has* gone by for Malcolm in every measurable way. At the same "time" (whatever that means) 15 years has gone by for Joshua.

What you said about Malcolm "appearing" to experience time slower than the observers on Earth is correct... IF (and this is a big if) you realize that everyone is just "appearing to experience time".

There is no "correct" time. Malcolm will experience time differently than Joshua, but neither is more correct than the other.

Perhaps we can say that the "appearance" of the rate of time is all we have got.

Malcolm's elapsing of 10 years is real in Malcolm's scale, and it is 15 years in Joshua's scale. Malcolm's elapsing of 10 years viewed from Joshua "appears" slower in Joshua's scale because Joshua's scale is not Malcolm's scale.

I think that is all we've got. If I'm bored time definately passes more slowly. And if that is the case, then we can say that time does exist, but it is unlikely that any two people will experience time at exactly the same rate, any of the time (so to speak).

I have noticed that our bathroom door seems to dilate time.

My wife (on the outside) experiences 2 hours, while I experience 5 minutes.... <<sigh>>

If you swing your foot it is younger than your heart.

It is my suspicion that time has an absolute existence as a physical aspect of the universe, as real as length or mass, and not just as a psychological phenomenon. This is over my head in terms of the physics involved, but the answer may lie within quantum electrodynamics. Perhaps e_brown knows more.

just 1 simple point:
if time travel to the past was possible, why aren't people from the future visiting us?Does this not mean that time travel to the past is impossible?

Perhaps...

Unless maybe the world ends next year. That would explain why no one from the future is visiting.

1) Perhaps there is no future. Maybe the world ends sometime shortly in the future -- or civilization is thrown into chaos by an asteroid hit from which we never recover.

2) How do you know people from the future are not visiting? Maybe they are but are unwilling -- or unable -- to be in contact.




Nope! For the reasons above.

One won't visit uninteresting time/places.
(What a shame for us.)

It couldn't exist, because the Universe/Space-Time is not clockwork and can't be 'wound back'. 2nd Law of Thermodynamics won't let you return chaotic systems back to an original state. Smash a glass and no amount of dials, knobs and 'anti-matter' will make it spontaneously reform.

Accelerating to an extremely fast speed, and maintaining that speed for a while, is the only sort of time travel that is possible, based on what we currently know.

If someone were to accelerate to 90% of the speed of light, for example, and mainatin that speed for a year, by the time they returned from thier little journey an entire lifetime would have passed on Earth. So, in a sense, that is time travel. They would be travelling into the future, in a way.

what about in a few million years time? a billion? a trillion? a sextillion... Would technology not have improved by then to enable people from the future to be in some contact with us. The main paradox is that the time in the future is "infinite" as it just can keep going on and on which means that if time travel was possible, then from the time it was invented onwards, streching to infinite amount of years, people would be able to visit us.
Another point: what would happen if i went back in time and killed my father and mother? i would not have exist, right? Then who would have gone back in time to kill my parents to prevent me form existing....

Playing the devil's advocate, perhaps the universe would not return to an earlier state, but one would be visiting an earlier portion of the timeline, which implies that the whole timeline is always accessible.

Well, then you wouldn't return to your 'past' - or even worse at that point, there would be no 'future' state to 'return' to. So, a single visit be a time-traveller to an event would wipe out the place that they arrived from, making their journey impossible.

You would have to have events 'fixed' eternally, or as each time-visit occured the entire universe would be changed.

Ok, so lets say time travel is possible, for arguments sake.
Let's consider two more questions:
1. What purpose would it serve?
2. Would it be possible to visit a time in the past (or future for that matter) within your own lifetime, and have two of you existing at the same time?

Another question: what would happen if i went back in time and killed my father?

Simply, it is impossible. Not everything is possible when back in time. The range of behavior is limited in space-time.