| From: matt | 17/06/99
16:35:26 |
| Subject: Time & Space travel | post id:
18383 |
| 1) If you went back in time and
changed something, would it change the present OR would the fact that you
changed the past have shaped the current present ie.NOT going back would
change the present. 2) Theory for Time Travel - you know that sci-fi thing about building the "Ring City" (Where there's a huge ring-shaped city/space station around the Equator supported on three legs)? If you built a mag-lev carriage inside that, you could build up some pretty good speed, right? Anyway, do you reckon we could do that fast enough to cross the date line multiple times in 24 hours?And would we then be in the future?Or the past?Or would it not work at all? Anyway... 3) Would a true spaceship have to be symmetrical, and it's mass centered about it's axis/axes? Cause if not, wouldn't it wobble or turn funny, being an absolute nightmare to turn or dock? That's it. Have fun thinking these ones through. | |
| From: James Richmond (Avatar) | 17/06/99
19:05:02 |
| Subject: re: Time & Space travel | post id:
18428 |
| 1. Since we are talking about
something which is probably impossible (reverse time travel), either
option could conceivably be correct. The only ways we could determine
which option is in fact correct would be (a) to build a time machine and
try it; or (b) to invent a really good theory of reverse time travel
(supported by other experiments) and look at what the theory predicts
(although ultimately we'd need to do (a) to be sure). There are other options apart from the ones you've mentioned here. For example, changing something in the past might start a parallel, diverging time line, meaning that you will change a "present", but not the same "present" as you were in before you started time travelling. 2. Crossing the date line multiple times in 24 hours is not equivalent to time travel, since on each circuit you "gain back" the time you lost by crossing the dateline. Astronauts in the space shuttle orbit the earth once every 90 minutes or so, but they don't time travel (ignoring relativistic effects). 3. A spaceship need not be symmetrical, but if it isn't this has to be taken into account in manoeuvering it, as you say. JR | |
| From: Chris W (Plebeian) | 17/06/99
19:09:58 |
| Subject: re: Time & Space travel | post id:
18430 |
| 1) Do the experiment and let us
know :-) 2) The international date line is not a time machine, just a convenient line drawn for political reasons. Let's say you circled the Earth for 48 hours at 10 km/sec and stopped where you started. It'd now be two days after you left. Not much of a time machine. 3) The craft does not have to be symmetrical in outer space. The main propulsive force must be applied in a direction that passes through the centre of mass of the object, or other forces used to correct for torque. Of course, symmetry and streamlining does matter in the atmosphere where frictional forces must also be balanced. | |
| From: Brett Hall | 18/06/99
1:40:11 |
| Subject: re: Time & Space travel | post id:
18475 |
| Whether time travel is or is not
possible may be a matter for the theoretical physicists. There are some
paradoxes associated with time travel (however it can now be argued that
the "grandfather paradox" (i.e: if you go back in time and kill your
grandfather will you cease to exist?) is not one of them. I take my cues from Dr. David Deutsch on this topic who is a proponent of the multiverse explanation of Quantum Physics (as well as the inventor of the concept of Quantum Computation) - who argues that if time travel is possible and we were to go back in time we would be *physically* prohibited from interacting with that time. That "time" has already happened and is set in stone and we are unable to alter it at all. Consider this example. Last Saturday you had a cup of coffee at home. Today is Sunday (say). Let's say you can travel back to *last* Friday. Let's say you were somehow able to remove all the coffee from your house so that on Saturday you would be unable to have your cup of coffee. This would mean that the Saturday following the Friday you have travelled to is in actual fact *not* the same Saturday you experienced *last* Saturday - because last Saturday you *did* have a cup of coffee (but this time around you won't as you removed all the coffee from the house when you went back in time to last Friday!) The problem is considerably more complex than this, however matt if you are interested in this topic you might like to head out to the library for: David Deutsch: "The Fabric Of Reality" Penguin 1998 Chapter 12 "Time Travel" for a detailed discussion. [ ISBN 0-14-014690-3] | |
| From: Daryn Voss | 18/06/99
1:53:04 |
| Subject: re: Time & Space travel | post id:
18480 |
| How's this for a suggestion?
Suppose we take a deterministic view that the 4D universe is set in stone. Suppose further that there is a "law of conservation of logic" that states that no such paradoxes can exist. If a man goes from year 2500 to year 2400, then he was always destined to do this, and in fact the effects of him emerging in 2400 were already in place in 2500 when he decided to go back. If this were the case, then a question like "What if a man went back and did something that prevented him from going back?" would be on the same as questions like "What if I designed a system that produced more mass-energy than it consumed?" The answer would be that such a thing would be against the laws of conservation. I suppose the only arguments against such a system being workable are that: (a) there are big problems with determinism, and (b) it is all a load of stupid nonsense. 8^) | |
| From: Chris (Avatar) | 18/06/99
11:16:09 |
| Subject: re: Time & Space travel | post id:
18502 |
Daryn -> You can eliminate the determinism to make it more attractive. Suppose you are to travel back in time. You could consider all the possible interacting paths back into time with their associated events, etc, as a series of unresolved possibilities - virtual paths, if you will. (If the reversed time troubles you, consider Wheeler's advanced and retarded wave theory). Travelling back in time results in the selection of a possible path and the collapse of the others. Now it doesn't really matter which quantum explanation you prefer - the mechanics are all the same - but it might be easier to visualise this with the "many universe" interpretation. Anyhow those paths which lead to temporal contradictions will collapse. Given that a sort of time symmetry has been introduced to the traveller's worldline by the travel, there isn't a problem with causation. The result mimics the determinist view you mentioned where reversed paths seem to be integrated into the time stream, and yet for once the quantum explanation makes more sense. Contradictory paths collapse, the time stream becomes symmetrical, and the resolved path seems to magically fit. Comments? Chris | |
| From: Cam (Avatar) | 18/06/99
11:26:04 |
| Subject: re: Time & Space travel | post id:
18507 |
| Sounds like a simple feedback
loop to me. Common in control systems. | |