Time travel !!

[danbaron]

Time travel!!..............................................................................................., is impossible.

(Who knows if this actually "closes the door" on the possibility of time travel - but, I thought it was impossible, and I think it is impossible, so I'll put the happy devil emoticon below.)

:twisted:

http://news.discovery.com/space/time-travel-impossible-photon-110724.html

[Charles Pegge]

The easiest form of time travel is sleep! Admittedly in one direction only.

[danbaron]

Yes, sleep. Also, anesthesia, suspended animation, death (assuming you can be re-animated). You can also effectively travel into the future by traveling from Earth in a spaceship, and approaching the speed of light (c). Depending on how close you come to c, and how long you are gone (from your point of view), everyone you knew may have been dead for hundreds of years when you return.

To me, there are so many seemingly logical impossibilities associated with traveling into the past.

If I get into a time machine and travel one minute into the past, will I meet another me there? If then, we both get into the time machine and travel another minute into the past, will we meet still another me there? If so, then, where did the atoms for the extra two me's come from?

Or, what happens if I get into a time machine and travel back to before I was born. When the time machine arrives, should it be empty?

My guess is, the past exists nowhere, and the future exists nowhere. There is only a continuous sequence of now.

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I forgot. I previously thought of sort of a way to travel into the past.

Maybe it violates quantum mechanics. But, anyway, I'll put it here.

(By the way, I'm pretty sure that according to quantum mechanics, two atoms of the same element are absolutely identical. In other words, theoretically it is impossible to differentiate between two atoms of the same element, which seems to me to be, pretty amazing.)

Say that on a particular date, in a particular town, you instantaneously record the type and position of every atom there. Maybe do it like this. Put the origin of the coordinate system, at the top of the pavement, somewhere in the middle of town. Then, at the specified time, you record the type and position of every atom within, say, a five mile radius spherical volume.

At some later date, maybe in a hundred years, you can reconstruct everything in the town (dirt, stones, pavement, buildings, ants, trees, cars, people, etc.) exactly as they were on that day and at that time, one hundred years previously. (And, you would not necessarily have to do the reconstruction at the same location.) You have a machine which instantly "spits" out all of the correct types of atoms into all of the correct (relative) positions. A person then walking into that town, would effectively find himself one hundred years in that town's past.

I think the problem is with the boundary of the spherical volume. As soon as you did the reconstruction, and set everything in motion, you would have an interface between the past and the future at the sphere's surface. The future, would flow across the boundary, and "contaminate" the past, so that the simulated past would diverge from the actual past. But, the larger the volume was, the longer it would take for the sphere's origin (center) to be contaminated.

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Bonus problem:

Say you are communicating with an alien in space, by radio. The alien is basically a humanoid (head, two arms, two legs, etc.). But, his internal organs are different in type and location. Is there any way to communicate to him which is his left arm, and which is his right?

[Charles Pegge]

Assuming we share the same organic chemistry, it should be possible to explain left and right to the extraterrestials in terms of asymmetric molecules like the amino acids.

Charles

[danbaron]

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I think that's pretty good.

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I read a book about Richard Feynman.

He asked the same question.

I couldn't find it now in the book.

I tried to find it online, and to my surprise, I did.

http://www.physicsforums.com/archive/index.php/t-247428.html

I think you can find an explanation towards the bottom of the page under, "George Jones".

[kryton9]

I never cared for the word impossible, especially in science. History shows over and over again whatever man can dream of, someday he can make it come true.

[zak]

there is an idea i read somewhere that the living being (not only the human) must be able to travel to the very near past ( a few microseconds) to be qualified as a life form. ie if we can't access the very near past realy then we will not aware of the existence either inside or outside. and when we sleep we lost our short time travel ability temporarily. yes we dream of the past but this is not a real time travel it is just the unrolling of the chemical memory.
i find this is possible , dan just contemplate a little of this possibility and you will find it of value, but without experimental evidence yet.
the continuous sequence of now means dust, and absurdity, and the negation of the "sequence" idea itself. if there is just now, then the original one pixel before the big bang must stay as it is without the need to expand to 3|4|5|...|D universe.
the duration idea itself encapsulates within itself the time travel idea.


and regarding the aliens , may be some aliens have different awareness than humans by a property that the alien brain units can travel to his past for 10 microseconds while we the humans for 5 microseconds, the cat may be 1 micro. so the aliens are completely different from us, not only from the biochemistry structure, they have different awareness than us ,and they look at us as we look at the cat.
the physicists can find a huge info if they focus on learning more from the living beings, but we will not bring their attention to this because of the huge agony they will cause to the mice, cats, ... .

[danbaron]

Of course, as Kent said, who can guess what a species a million years ahead of us can do?

When I said there is only now, I guess I meant in terms of being able to interact and change events. We have memories of what previous nows were like. But, as far as we know, we cannot cause the previous nows to again become the current now, so that we could in any way alter them. In other words, I think the past and future have no existence - they are not located at some place that we can travel to, and then either change the past, or, view the future. Just from your life experience, have you ever been able to change even the tiniest detail of the most trivial event that has already happened? Similarly, how is it possible to travel to the future, if, by definition, the future has not yet happened?

A person could make the case that a video recording is equivalent to traveling back in time. But, I think the difference is that when you watch it, you are only viewing what previously happened. You have no ability to interact with it or to change it. Similarly, in the future I think we will be able to make holographic records of events. Then, you could in a way potentially walk around within previous events. You could feel that you were part of them. I think the difference would be that you could not interact with them. Your actions could change nothing. And, no matter what you did, the holographic people would ignore you.

I can again make the case that it is impossible to prove that the universe did not begin just one second ago. Everything could have appeared one second ago exactly as it is - people, records, memories, fossils, buildings, etc. It would be impossible for us to know it. Of course, in that case, it would seem that the perpetrator was trying to fool us. But, I think he could be successful.

In terms of torturing animals as part of scientific research, medicine has been doing it since probably, the beginning of medicine. And, medicine will continue to do it (especially as long as there is a source of money for doing it). I think it is absolutely morally wrong, and, I would never condone it. Actually, I think it is morally wrong to kill animals for food, too. (And, I think that in the future (if there is one for humans on Earth), people will view us as savages for enslaving and eating other species.) The people who do that "research", I view as sociopathic - it isn't them who experience the suffering, so, as far as they are concerned, it's a beautiful day! And, you could ask the question, "If a person feels no compassion for animals, is it likely that he feels it for other humans, regardless of the way he presents himself?".