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Mr. X
2001-Oct-28, 05:33 AM
Doesn't the Bad Astronomer ever tire from being right all the time?

There was some astronomy in the movie, and if I remember correctly some bad astronomy, but unlike some people (wink wink) I do not take notes of bad astronomy during an otherwise rather enjoyable movie.

There was some BA, probably more Bad Physics but I don't remember the exact thing I wanted to remember about it. /phpBB/images/smiles/icon_smile.gif

Oh yes, at some point he says they travel at superluminal speeds (quite clearly), yet afterwards he says the voyage took 7 years. He even compares his speeds of voyage to tachyons, mythical particles with an imaginary mass that would travel faster than light. From what I have read on tachyons it has been said that they would also travel back in time. [Conlusions should be drawn here].

This is getting very complicated, as it's two in the morning, I am tired and my brains are off-line. Could someone complete these thoughts for me please!

Donnie B.
2001-Oct-28, 01:25 PM
I think it's fair to say that tachyons (if they have any physical existence) do go back in time. Remember that in the relativistic universe, time is defined by the velocity of light in a vaccuum. Photons are timeless; they leave Sirius and enter the Hubble telescope at the same time (from their perspective). Therefore anything that leaves Sirius when those photons do, and gets to Hubble before them, must do so in t < 0.

Mr. X
2001-Oct-28, 01:51 PM
Some confusion arises from this. If you took a ship that traveled nearly as fast as light your time would go really slowly. At lightspeed his time would be stopped. So he would instantly be there. To him, I guess his time would seem to continue normally.

Now above the speed of light his time would go backwards. If he didn't notice it the two other times, why should he notice it now? The condition is very special but he wouldn't see it. Or would he?

By induction from the other two cases I'd say he doesn't notice it, yet he arrives before he left. A round trip of a certain time would place him back on his planet perhaps some time before he left. Or it could be calculated just to come back immediately after he left.

Um, right?

James
2001-Oct-29, 02:04 AM
On 2001-10-28 08:51, Mr. X wrote:
A round trip of a certain time would place him back on his planet perhaps some time before he left. Or it could be calculated just to come back immediately after he left.

Um, right?

I think that he would arrive home before he left if he were to make the trip home right away. I would say that if he wanted a little time to elapse on his home planet, he'd just stay at his destination for some time. /phpBB/images/smiles/icon_confused.gif /phpBB/images/smiles/icon_confused.gif /phpBB/images/smiles/icon_confused.gif

_________________
Calling evolution a religion is like calling baldness a hair color.

<font size=-1>[ This Message was edited by: James on 2001-10-28 21:06 ]</font>

Wally
2001-Oct-29, 12:04 PM
The website below describes the author's idea's on what might prevent paradox's from occurring in faster than light travel. Pretty interesting stuff, and a great primer for those interested in SR. . .

http://www.physics.purdue.edu/~hinson/ftl/

SeanF
2001-Oct-29, 02:27 PM
On 2001-10-28 08:51, Mr. X wrote:
A round trip of a certain time would place him back on his planet perhaps some time before he left.

Um, right?

Um, why?

The time dilation effect is on the traveller, not the rest of the universe.

That is, if two planets are four light-years apart, and you travel between them at .5c, sixteen years will pass on the planets (eight out, eight back), but fewer for you (about thirteen years, I think?).

If you travel between them at 2c, four years will pass on the planets (two out, two back). Presumably, since you're travelling at superluminal speeds, "negative time" would pass for you (whatever that means), but everybody on your home planet would still be four years older when you got back . . .

Wouldn't they? /phpBB/images/smiles/icon_smile.gif