Time Travel?

Question

Just a thought here. Is it possible to travel back in time by circling the Earth around the equator, going over the International Date Line, faster than the Earth itself is spinning. (I know, it's a scenario from an old Superman film, but is it possible all the same - surely, if you can do it in less than 24 hours, you will cross the International Date Line twice, backwards, in 24hrs so you are two days back in less than a day)

I not only want to know if it is possible or not - but also WHY? I have a feeling that you can't, as astronauts orbit the Earth very fast, yet do not travel back in time. WHY?

Answer 1

No, the Prime Meridian is irrelevant. You first have to remember what Einstein said when asked what the definition of time is: “It is a phenomenon that you measure with a clock”, was his reply.

Way back when I was taking physics in undergraduate school we talked at length about time. I do not remember the exact functions or principles that were involved but it was demonstrated that as an object approaches the speed of light, the passage of time changes relative to objects moving at “normal” speed (the two clock theory). Of course the change is very slight and as the object decreases speed the phenomenon disappears. Perhaps some Physicists out there can shed some “light” on it.

I personally do not believe in "time travel". The event is now, the future is only a forcast and the past does not exist, only the results of what happened in that "now".

One additional point. I have a BSEE as well as a couple of other worthless degrees, one being in laser optics. I was always confused about light and its properties. Since light energy acts not only like a wave but also as a particle and has mass, how is it that light particles travel at the "speed of light"? It is possible for light to travel slower than lightspeed but is it possible for it to travel faster?

Answer 2

Let's just blame superman and give you a break. No its not possible. Superman was supposed to pull off the trick by going faster than light - now some non-scientific types have concluded that as time gets slower as you approach the speed of light flying faster means you will go backwards in time but nothing with mass can accelerate past (or even up to) the speed of light.

In fact because time doesnt pass at light speed (remember spacetime is a combined entity and if you're travelling at that speed all your movement is through space and none left through time) you wouldnt be able to say 'a little bit faster!' you'd just experience the whole universe in an instant. If Superman could accelerate up the speed of light he'd never be able to stop because the whole universe would be over in an instant from his perspective and Lois would be even more dead. Its only the speed of light that makes it plausible (superficially) going around the dateline takes time, it doesnt make you go back in time. Phileas Fog gained a day but you cant exactly say he went back in time. You'll come unstuck if you get your physics from dodgy movies! Besides Lois wasnt worth saving. Now at least Mary Jane liked Peter Parker and not just Spiderman - Lois Lane is shallow and horrible.

So no. No, its not possible. If you want to read about time travel I can suggest the fabric of reality by David Deutsch.

pcpy - Photons dont have REST mass. Thats where you're getting confused. You can say they have mass because they have energy and E-mc2 but they're not made of matter in the same way in which a neutrino or proton is.

Answer 3

Theoretically if you can travel faster than the speed of light you could go backwards in time. . There is a currently a professor at Harvard, Lisa Randall, doing research (in conjunction with a few hundred other scientists around the world) on the concept of dimensions. It might shed some light on this topic. However, "presentist" hold that there is no time but the present, and that time is a man made concept. Hence the past and future do not exist to be explored.

Answer 4

No, the international date line is an arbitrary line which was created by people -- just as time designations are created by people. It's actually the same -time- everywhere (for all practical purposes) at any moment in -time-... we just have different times in different places to reflect the fact that the sun shines differently on different parts of the earth AT THE SAME TIME.

Even if you flew around the earth faster than it was spinning and passed the international date line, time would still be passing at pretty much the same speed for you and people on Earth. So if you flew around the Earth at 3:00 pm Pacific Time and did it in one minute, it would be 3:01 Pacific Time when you got back to where you started.

Answer 5

I've got a time machine, but it went wrong tomorrow.

Seriously, though, according to Einstein and others, (a) you could do it if you travelled faster than light, (b) but you can't travel faster than light though (c) while your are winging your way round the world, time will pass by at an (imperceptibly) different rate, so you will not be quite the same age when your trip round the world is over as you would have been had you stayed put. Are they right? I don't know, and my car isn't fast enough to test out (a) or (b), and nor is my watch accurate enough for (c).

There was a young fellow called Bright,
Who travelled much faster than light,
The physicists say
That he went out one day
And came back the previous night.

Answer 6

I note that the majority of the respondents have already pointed out that the international dateline is man-made definition. Even if you were able to fly fast enough to travel the dateline twice in a day you would keep returning to the date when you started your journey.

However, if you are really interested in time travel a good book to read is Professor Stephen Hawking's "A Brief History of Time". Theoretically, if you were to travel into a black-hole, time inside the hole would appear to slow down.

Answer 7

No. As you travel it is taking you just as many days to complete the journey. This means you have only moved the same distance that the Earth has revolved over the same period. Now that that sounds like you haven't moved at all. But in reality it has still been the same distance-only in the opposite direction.
Its a bit like if you walk to the front of a jumbo jet, are you walking at 500mph?. If you walk towards the tail, how fast or slow are you walking?.
Its a paradox!!!.

Answer 8

Your personal time in relation to a stationary observer will be a teeny tiny bit slower due to relativistic effects (reduced gravity and increased velocity), but this time difference is largely negligible. So, your personal time and time for us folks on earth is, in all practical aspects, progressing at the same speed.

The international date line is an arbitrary datum which determines the calendral date in relation to the Earth's rotation. It has no relevance in terms of the progression of time, except from a clerical perspective.

Ta.

Answer 9

The Date Line is an imaginary convention of society. Simply flying around the earth in any direction does not imply time travel.

Answer 10

No. You haven't thought this out have you ?

You seem to think that crossingthe IDL means you go back in time. It doesn't. For us, time is always going forward.

Suppose you are in London and its 5pm Friday. Whiz round the planet in 1 minute coming back to London. Its now 5:01, still on Friday. Its not Thursday or Saturday, its just one minute later on Friday. If you went Eastwards, you will reach a place that has midnight on Friday. The next point it will be early saturday. Then you come to the IDL. Cross it, and its 00:00 Friday again. Keep going till you get to Friday 5:02 in London.