Thursday, April 16, 2009

Time Travel - Part 2


Casey and Brett are right, time travel into the future is possible. See below for an excerpt from Scientific American:
"The Twin Paradox is arguably the most famous thought experiment in relativity theory. In this supposed paradox, one of two twins travels at near the speed of light to a distant star and returns to the earth. Relativity dictates that when he comes back, he is younger than his identical twin brother.
So the star six light-years away to the homebody appears to be only 4.8 light-years away to the traveler at a speed of 0.6c. Therefore, to the traveler, the trip to the star takes only eight years (4.8/0.6), whereas the homebody calculates it taking 10 years (6.0/0.6). It is instructive to discuss how each would view his and the other's clocks during the trip. Let's assume that each has a very powerful telescope that enables such observation. Surprisingly, with careful use of the time it takes light to travel between the two we can explain the paradox.
Both the traveler and homebody set their clocks at zero when the traveler leaves the earth for the star (event 1). When the traveler reaches the star (event 2) his clock reads eight years. However, when the homebody sees the traveler reach the star, the homebody's clock reads 16 years. Why 16 years? Because, to the homebody, the craft takes 10 years to make it to the star and the light six additional years to come back to the earth showing the traveler at the star. So to the homebody, the traveler's clock appears to be running at half the speed of his clock (8/16.)?"
Still confused? It has to do with the amount of time it takes light to travel. It works just like sound. When there is an explosion miles away, the sound happens instantly, but the sound waves have to travel to your location in order for you to hear it. But by the time you hear it, a few seconds might have gone by since the explosion happened. Light is the same way. Many of the stars we see in the night sky might have already burned out, but in some cases it takes millions of years for the light to reach us, so our perception of events is happening at a different 'time' than those of the star.
So Nancy, to respond to your last comment, you can't travel backward in time because what has happened has already happened. But you could hop into a vehicle going near the speed of light and come back 20 earth years later to check out the scene... But don't expect to see your future self to see how life turned out, because there is only one of you. And when you left us here on Earth in 2008, you did not return until 2028. And I am assuming that the US had by that time fully embraced Communi...oh sorry, I mean a progressive system of government where everyone is truly treated equally and no one has the opportunity to get ahead, well except for the people in charge.

34 comments:

  1. Are you saying that only a twin can travel close to the speed of light?

    Doesn't anyone watch Lost? Time travel definitely swings both ways.

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  2. Very interesting article. So does this mean the time traveling brother will only age 8 years? This gives me a headache and makes me want to find my copy of A Wrinkle in Time. Also, I liked that even though this was an article about time travel you were still able to incorporate your political views. Bravo! I think you have this blog thing down :)

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  3. Very well said Jake. The thing about this whole topic is that you are not really traveling through time as much as you are changing your own perspective on time by altering the contributing factors that dictate how time is perceived.

    I had to vote for you Jake on the new poll. There is no way I could keep my focus with you drunk, running down I-35 in an all silver jumpsuit.

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  4. The example used doesn’t make any sense to me. Why is the relative distance to the traveler 4.8 light years? If he is going 60% the speed of light, how would he ever be able to say that he is less than 6-light years away from a star that is 6-light years away? Wouldn’t that require him traveling faster than the speed of light? Maybe I am wrong here but I thought that a light-year was the distance traveled at the speed of light for 365 days.

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  5. JB, he is six light years away from the perspective of the twin brother that reamins on earth. Since time is slowing down for the twin that is traveling, the light travels farther in the same amount of time. Remember, the speed of light is constant, so if the time is slowing down, then the speed of light per some measurement of time must increase.

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  6. I need to have this conversation live. This is the one set-back to the blog. I like bouncing things back and forth for immediate response and comments.

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  7. And I'm really having problems understanding how the traveler is 4.8 light years away from a star that is 6 light years from earth when he never goes faster than the speed of light.

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  8. JB - don't focus on the distance, but rather the clock that each of the twins has. The distance to the star is still x miles away. But the time that each twin experiences is different. Because from the homebody's perspective it takes more time for the traveler to reach the star because the light is having to travel back for him to see it whereas the traveler is experiencing it real time.

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  9. Correct me if I wrong, but if the brother that traveled to the distant star, immediately departed for the return trip to earth, the round trip would take 16 years, right? Would it not then be possible to "observe" (in the giant telescope) his arrival in both places at approximately the same time?

    If this is true, I wouldn't consider this time travel, but rather a limitation of what is perceivable with the human eye.

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  10. OK, let me try to explain a little better since I was apparently not convincing enough. The speed of light is constant. But when we say that that light travels however many miles per hour or this far in a year, we are taking a constant and measuring it with our own perceived notion of time. Since time is relative, and can change, that means that light years or mph for speed must also change to keep the ratio the same. Basically, the speed of light is remaining the same and is being perceived differently in relation to time. He would not be traveling faster than the speed of light, because in his "time" the speed of light is that much faster.

    This would be way easier to talk about live, but unfortunately we do not all work at the same place JB, so get over it.

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  11. yeah or Brett will blow up your house...

    And screw all of you people! You think the only way I can beat Brett is with an all silver jumpsuit? Granted, it would make me a lot faster, but I think I would even have a shot without it.

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  12. But why would the twin on Earth see a different time on the clock? When it is 11:00 on the travelers clock, the earth twin will see "11:00" but it will be x years later, where x is the distance in light years from earth the traveler was when his clock said 11:00. The time gap between the two clocks I think is well-illustrated by the purple and pink lines in your graph above. As the earth twin watches the traveler's clock and the traveler starts traveling at his desired speed, the traveler's clock as perceived by the earth twin will slow down and the minutes may eventually take hours, days, etc as the traveler continues to get further and further away and the light takes a longer time to reach earth. However the reverse happens when the traveler returns to earth. As the traveler gets closer and closer, the minutes start to speed up to the earth observer until they finally catch back up to the relative earth speed when the traveler returns.

    I think your graph represents this well but I think that the traveler's clock line should run from 0-20 years and meet back up with the earth's clock. Now if somebody can explain to me why the star is perceived as 4.8 light years away for the traveler to begin with then I may be able to admit that time has to change.

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  13. To the person from earth, the star is 6 light years away and the ship is traveling .6 the speed of light, therefore the trip takes ten years and the roundtrip takes twenty years.

    To the traveler, it looks from the example that time slows down 20 percent. So now what was 6 light years away is now only 4.8 lightyears away. He will perceive the trip as only taking 16 years and will return to earth 4 years younger than his twin brother.

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  14. Yes, as the traveler returns to Earth, the clock speeds up until it is spinning at the same rate as the homebody's clock. But that doesn't account for the time that was already lost on the journey to the star or the partial trip back when the two clocks were off. That's where the missing years or the time travel enters in. The return trip does not undo the time that was lost on the way out there...it just brings both brothers back into the same frame of reference.

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  15. To anyone out there reading this and wondering what the hell is going on, this is what our entire high school and college years were like. Arguing/debating about random things including the mysteries of the universe.

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  16. Would it really be worth it to spend 16 years (your time) on a spaceship just so you could time travel 4 years into the future? We need a faster ship.

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  17. All you have to do to admit time is changing is accept the fact that it has been proven numereous times. Not only with atomic clocks, but there have also been experiment where they take smaal amounts of elements and have them travel in those accelerators for a long period of time. When they finish the experiment, they find that the element has not decayed at the same rate that it should have, and is infact younger because of the change in speed.

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  18. The traveling twin will always take 6 years traveling at the speed of light to reach a star that is 6-light years away. The traveling twin still has to spend 365 days relative to himself going the speed of light to make this happen. I still don't understand how the 4.8 is valid.

    Where was time lost? The gap in visible time between the traveler and homebody clock is only because of the limitation of the speed of light. If it were possible for immediate, direct communication between the two twins during the entire voyage, when would there be 4 years of communication lost? There wouldn't be. Both twins would be able to verbally report the current time and date to each other 24 times a day and they should be dead-on for the entire 20 years. But when the traveling twin says "It is 8pm on 4/20 and I am currently waving my arm" then the homebody twin will hear this immediately, confirm that it is indeed 8pm on 4/20 on his clock but then wait for x number of years before he sees the traveling twin wave.

    I just think that this kind of time travel is not actually time travel, but like Keith touched on, is more a limitation to what we can perceive. Because we perceive what we are currently viewing as "now" but the limitations of the speed of light (which allows us to see) gives us the situation where when you see a star explode, you are witnesses an event that happened in the past.

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  19. Sign me up, although...my doctor said I can't do space travel...can we build one of those ball things like in Contact?

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  20. OK Justin, You are staring to upset me.

    A. Where were you when we argued this in high school and basically disproved everything you are trying to argue now? You are making the same arguments I made before we really started looking into this and found the truth.

    B. Do you just not believe what we have talked about with the atomic clocks reading different times and the rate of decay slowing when elements are put in accelerators. These are actual tests that have been conducted, no longer just theory.

    C. You will never be able to accept that in the traveler's perceived time he is only 4.8 light years away until you can accept the fact that time is relative. If time is not relative, you are correct...this is impossible. But it is really just simple math. If the speed of light is constant and the time measured can change, then it is not hard to see that 6 light years to one person can be 4.8 light years to another that is perceiving time differently.

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  21. Can we please reenanct every one of these blog conversations on the river this summer?

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  22. The faster you go, the slower time goes for you. Time is relative and is directly related to your speed. The traveler doesn't feel younger, he is younger. Less time has passed for him, 4 years to be exact. He has not aged as much as the homebody brother.
    For example, when I race Brett in my silver jumpsuit, the faster I go the less quickly time will pass for me because I will be going so fast. You might say that this difference would be imperceivable to me, but I would respond with you have never seen me run in my silver jumpsuit. I am very fast.

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  23. I understand everything in theory it just doesn't make fundamental sense to me. And yes, I realize that I am not a physicist or a relativist. I guess I am not sure I am ready to accept that time is relative.

    The atomic clock experiments are very interesting but obviously they are not concrete evidence that Einstein's theory is proven, otherwise we would not be having this discussion. However, from what I read, there has been nothing found to show that Einstein's theory would not work if we had the means to try. There are also other theories about infinite alternate universes that all co-exist that capture every possible outcome of a situation. This is said to explain some paradoxes such as killing your mother because you are simply creating another universe in which your mother is now dead but there still exists a universe where you mother is alive and gave birth to you, thus allowing you to go back in time and kill her later.

    I think you have to keep in mind that Einstein's theory is just a theory and we can not yet prove it one way or another with our current technology. While there may be evidence supporting the theory and many scientists devote their lives studying and analyzing, it still cannot be proven. Sounds kind of like Christianity to me. Oh no he didn't!!!

    Also, nobody has argued against my instant communication example. It may be wrong but I think the question has merit.

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  24. When are we getting the next baby picture

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  25. Yes but Eistein's theory isn't about traveling into the past, so the mother paradox is irrelevant. Interesting that you chose mother...

    The alternate universe thing you mentioned has to do with string theory. I also find it very interesting and will do a post about it.

    I can accept the time travel theory as well, but it's very hard for me to accept the implications of what it actually means. It's insane.

    I don't think your communication thing makes any sense because it would have to travel faster than light for it to beat the speed of them seeing each other. Instant communication is an oxymoron. There is no such thing as instant (except instant rice, it's pretty fast) anything. Everything, including sound and light takes time to travel for one point to another.

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  26. I'm going to have to reserve the rest of my questions/comments to the first river trip. This is too great of a topic for blog comments to do them justice.

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  27. Perhaps you guys could set up a conference call and work this out, or go rent Carl Sagan's "Cosmos." If you're really trying to understand this, a blog isn't the best way.

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  28. Also, the instant communication thing, assuming it would even be possible, wouldn't work because when the traveling twin says "It's 8am" the homebody twin will say "no, it's 10am", because their two clocks will be different.

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  29. That's the problem is that Justin doesn't understand that these two people are not experiencing things at the same time. So instant communication is not possible. And Casey, technically, it could be 8am where both twins are, but they would probably need to clarify the day, month, and year.

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  30. Justin, Einstein's theory of Relativity is a lot more complicated than time dilation. Time dilation is only a piece of his theory and if the experiments that have already been conducted do not prove that time dilation exists I don't know what you want.

    There is no reason to argue against your instant communication argument because the atomic clock experiments prove that you are incorrect. You can say that the clocks are just malfunctioning, but that doesn't explain the rate of decay slowing down in elements tested at high speeds.

    And as for it not making fundamental sense to you...welcome to the club. I doubt there are very many people on the planet that this makes fundamental sense to.

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  31. I'm really satisfied that I played a part in breaking up the two love birds. Now that you guys aren't finishing each other's sentences perhaps I can try out my debt-free blog again.

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  32. What we need is a worm hole! I found a video of a guy who found one. http://www.youtube.com/watch?v=E2sp-clMk8s if an old man and a young man having the same tattoo doesn't prove it, I don't know what will!

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  33. Jake wants to know if he can have his blog back.

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