If you had a time machine…

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    Profile photo of RevMen

    “Brian of Paco” wrote:
    anyone understand the logic behind that? if speed is relative, then how the hell can there be a limit to how fast you can go?

    It has everything to do with energy. Einstein really came and screwed everything up with his relativity theories. In Einstein’s world, energy and mass are two versions of the same thing (e=mc^2 and all that). (I’m going off of memory here, so I might get some of this stuff wrong) Mass, instead of being its own thing, becomes something called rest energy. As you speed something up, more of its rest energy becomes kinetic energy. Eventually, when you reach the speed of light, you’ve got all kinetic energy and no rest energy, and so there’s no way for it to be any faster. At least that’s how I remember it.

    People often sum up the relativity theories by saying “everything is relative” or “speed is relative.” This is very far from the truth. It is possible to have an absolute speed, which would be speed with respect to the universe. All of our usual equations for speed and acceleration are designed around the concept of choosing a point of reference, and so that’s the way we think. For the vast majority of cases, they work fine. Same with Newton’s gravity equation, for the great majority of applications, it’s fine. Problems start to arise when you deal with extreme speed or gravity. That’s where Einstein made his “adjustments.”

    The key to understanding special relativity is the speed of light. The most important concept is this: no matter where you are or how fast you’re going, light will appear to you to be traveling at 300k km/s.*

    So what if you’re in a car that’s going 200k km/s and you have your headlights on? Does the light from your headlights appear to be going 100k km/s? Nope, to the person driving the car, the light from the headlights is moving away from the car at 300k km/s.

    So what if I’m standing by the side of the road and you go zooming by me at 200k km/s, does that light appear to be going 500k km/s to me? Nope, if I’m standing by the side of the road when you go zooming by, the light from your headlights is going 300k km/s and your car is going 200k km/s. To me standing by the road, you are indeed going 2/3 the speed of the light from your headlights.

    These seemingly contradictory points of view are reconciled by
    1) A change in time, which has been discussed quite a bit here and
    2) a change in length, which is really freaky. I don’t remember enough about it to explain it clearly, I’m too lazy to go look it up, and I’m not sure anyone’s interested in reading about it here.

    *In a vacuum. Light actually moves a little slower through gases and liquids. This gives rise to a very cool phenomenon called Cherenkov radiation. It happens when subatomic particles travel through a medium at faster than the speed of light for that medium. The particles are still traveling slower than the speed of light in a vacuum. Cherenkov radiation is a very pretty blue glow that comes from whatever liquid or gas the particles are traveling through. If you’ve ever seen the blue glow from a nuclear reactor core, that is Cherenkov radiation. I have personally seen a Cherenkov glow when I looked into the core of a training reactor at the Budapest University of Technology and Economics where I was studying abroad. Yes, I looked directly at the core with no barriers of any kind blocking my view. The power from the reactor was very small, as it was only a training reactor, but radiation is radiation, and I couldn’t stay for very long. It was the truest color of blue I will probably ever see.

    Ever seen or read Starship Troopers? Their ships were powered by a “Cherenkov Drive.”

    Profile photo of Flash1015

    I don’t know, Doc Brown and Marty Mcfly make it pretty obvious that the future is more of “Random” events then a set plan, but back on the “setting the molecules to it’s exact spot and order to go back in time is pretty interesting to me” Maybe it’s possible to Isolate a chamber and then rearrange the particles in there to go back in time, Then you can brag to your friends saying you were breathing air from 2 weeks ago 😉

    also, very interesting Paradox Cometgreen maybe you should have a discussion with Phillip J. Fry from Futurama and he can tell you his grandfather story.

    Profile photo of Cometgreen

    *gives a Kudos bar to flash* 😉

    Thanks for that more indepth explanation Revmen. I’d like to see one of those reactors too, it sounds pretty cool. At least I’ve now learned a little bit about Cherenkov radiation.


    Profile photo of Drunken Farmer Ben
    Drunken Farmer Ben

    “legogod” wrote: Now, a movie explains (and doesn’t explain) this principle very well. Donnie Darko is THE best film about time travel I have ever seen. I recommend it to everyone who has answered this thread, and even those who think daily about time. If you like it enough, I’d be happy to discuss it through email or PM.


    Geez, that movie is confusing 😕 And that bunny was scarry :-( But it was good when at the end it all came together (just to be screwed up again at the very end 😮 ) (NOTE: Parts of the movie aren’t really appropriate for younger kids. You’ve been warned, so dont come to us :P)

    I just need to replace my flux capacitor, and I’m good to go!

    Profile photo of Stefan

    RevMen missed a small point: depending on your definitions, Einstein’s most famous formula is not relativistically correct. It should read

    E = gamma m c^2, where gamma is 1 over the square root of 1 – gamma^2/c^2.

    That square root is what causes all trouble in the theory: as the speed approaches c, the number under it goes to 0 and consequently the energy approaches infinity. Another way to look at it is that your mass increases as you approach light speed. Accelerating further costs increasingly much energy, and reaching light speed costs an infinite amount of energy. Only particles with absolutely no mass (photons) can therefore travel at light speed. It is debatable whether wormholes will solve this problem, but new theories of physics (most notably string theory) might provide workarounds by introducing a set of new dimensions, which are curled up…

    Confused yet? Donnie Darko (which I saw only last week, and which is one great film) certainly won’t make things clearer! I was most puzzled by the man in the red suit: why does he re-appear just when the party starts?

    Oh, personally I’d travel about 20 to 30 years back and buy all these great sets at retail-prices!


    Profile photo of Cometgreen

    It is debatable whether wormholes will solve this problem, but new theories of physics (most notably string theory) might provide workarounds by introducing a set of new dimensions, which are curled up…

    Hmm, never heard of the string theory. I think I’m gonna have to look that up.

    And thanks for introducing that gamma into e=mc^2; it now becomes all the more confusing. :(

    Cometgreen, making the third page

    Profile photo of timdrage

    “Drunken Farmer Ben” wrote: So, why not steal our lego collections from ourselves, and have twice the Legos! And when we steal them from ourselves in the future, we will have the set we stole from ourselves in the past.

    Ah, but this will cause a feedback loop which will destroy the fabric of time + space, thus:
    When you steal your own Lego, you will then later have twice the amount, granted. But then, when you come to the future to steal it you will steal that double amount, and then end up with 4 times the Lego… but then you’d have stolen that amount, + thus actually have EIGHT times the Lego! And so on until the entire universe is solidly filled with LEGO and all other matter is extinguished!

    Profile photo of NewLegoCinema

    But…If your time machine didn’t have a time sheild,the whole world would warp into the furture with you.If you watch the end of The Time Machine(2001),The Uber-Morlock’s Arms are inside the time sheild while the rest of his body is outside.When Alexander pushes the lever forward,everything outdside of the time sheild moves forward in time.Because Alexander is going through thousands of years,the Uber-Morlock disindigrates,but his arms are still in the time sheild.
    Also,in the same movie,Alexander’s little picture of Emma falls out of the time sheild.Alexander tries to grab it,but his fingernails grow.
    In THAT SAME MOVIE( 😆 ),When Alexander tries to go back in time to save Emma,she gets run over by a cart.When Alexander sees the Uber-Morlock,he tells him that if Emma was alive,he would have no purpose to build the time machine.

    Profile photo of Marty

    Once you open this can of worms it’s amazing what comes out of the woodwork, fact! Time travel, in theory, is the only thing that has been proven, in 1960’s I think?
    But there is another theory thats been doing the rounds for a while, it’s called timeslips, I won’t go into details, but there have been some well documented cases about this, most of it has to do with seeing the past or future, infact it would explain why people see things before they happen or think they have seen ghosts, spooky eh?
    As for time travel itself, I think if you want to travel then cyro-genics is the way to go, providing they ever get it right and you don’t end up like mush.
    Hey! It’s a one-way trip with out the jet-lag. Another possiblity is to send a radio message back through time. Fact, they are already working on this. Just a bit of trivia, Marty

    Profile photo of Brian of Paco
    Brian of Paco

    bah, time to start my own branch of theoretical physics, stupid einstein

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