Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Simple time theory questions

  1. Jul 29, 2009 #1
    What happens to time at the speed of light? If a person is travelling at a high speed do they age faster or slower relative to a stationary person? Is it theoretically possible to stop time?
  2. jcsd
  3. Jul 29, 2009 #2


    User Avatar
    Homework Helper

    Well, I can say this: if you see a person traveling past you at a high speed (relative to yourself, of course), then you will observe them aging slower than you are. But that person will see you traveling past them at a high speed, and therefore they will see you aging slower than they are. It sounds strange but this is actually possible (and real) because there is no "absolute time" to fix one particular rate of aging that all others must be measured against.

    As for stopping time... consider that person from the last paragraph. The closer they go to the speed of light, the slower you see them aging relative to you, so you would think that if they ever actually reached the speed of light, you would see them not aging at all. But it's impossible to actually reach the speed of light, so it's kind of a philosophical question, not a physical one.
  4. Jul 29, 2009 #3
    If you travel with the speed of light, you will see the infinite length contraction of space in the direction you are traveling. So you get to your (final) destination in no time.

    You will also suffer the infinite blue-shift radiation coming head on. And see nothing else in any other directions.

    If you can send back your signal, other people will see you moving at the speed of light, frozen in time, and reach other places in finite-time.
  5. Jul 30, 2009 #4


    User Avatar
    Science Advisor

    If you travel at the speed of light, you are not living in our universe.

    The question is about as meaningless as what's north of the north pole.
  6. Jul 30, 2009 #5
    To ask another way. If we could attach an atomic clock to a photon and start timing the instant the photon leaves the surface of the sun, how much "time" would pass, from the photon’s perspective, before it hits our eyes on Earth?

    And please don’t respond with “if you could attach a clock to a photon, you don’t live in our universe…”
  7. Jul 30, 2009 #6


    User Avatar
    Science Advisor

    If you could attach a clock to a photon, you don't live in our universe.

    Seriously, I'm not just giving a flippant response, this question is just as meaningless as the other one. It is IMPOSSIBLE for anything with mass to travel the speed of light. It is MEANINGLESS to ask what things "look like" in the frame of the photon (or any particle moving at c).

    The only similar meaningful questions are what happens as you approach c. As velocity approaches c, the proper time to travel between any two points shrinks arbitrarily close to zero, but this does not imply that a photon experiences "no time", because to ask such a question is (see paragraph 2).
  8. Jul 30, 2009 #7
    Okay, so if I ask the same question but change "photon" to "neutrino" and "c" to "nearly c" - The clock would read something arbitrarily close to zero.

    So from the neutrino's perspective, it takes – arbitrarily – almost no time to traverse 1 AU, while we would time that journey as something slightly over 8 minutes. Or am I still off in my own universe?
  9. Jul 30, 2009 #8


    User Avatar
    Homework Helper

    No, that's right. From the neutrino's perspective it takes a very small amount of time to traverse what we would measure as 1 AU. (How small exactly the amount of time is, of course, depends on how fast it's traveling)
  10. Jul 30, 2009 #9
    Thank you diazona, this is my first day on this site. very cool. Now I need to find where the "absolute rest" discussions are hiding. (i know, i know - not in this universe)

    So many questions, so few physics classes…
  11. Jul 30, 2009 #10
    Thanks, that was helpful.
  12. Jul 30, 2009 #11
    Heres what I am getting at, we are basing all of our knowledge on our size. If you had a motor in space spinning anything with a circumference of 186,000 miles at 60 rpm there is the speed of light. Why wouldn't the earth be twisted inside due to time infraction in the core vs. the surface? If there is a time infraction twist does it pull inward or push outward. It, to me would look much like the milky way if this were true. Is there such a thing as time related friction? Sorry for the disjointed thought, I just spent all day grinding steel in a factory and the beer went down easy.
  13. Jul 30, 2009 #12
    Thank you for putting that in simple terms, I am just a thinker with no math background. Trying to digest it though, I'll post later.
  14. Jul 30, 2009 #13


    User Avatar

    Staff: Mentor

    That is a violation of special relativity and so impossible. As the object spins faster and faster, it takes more and more power to continue the acceleration.
    I don't understand any of that - it sounds like gibberish.
  15. Jul 30, 2009 #14
    i think he's asking if time moves slower on Earth's surface than in the core due to the difference in rotational velocity. If so, what would be the implications?
  16. Jul 31, 2009 #15
    Exactly, if you stretch a rubber band, there is energy expended and that energy becomes heat. So does the time differential stretch of the earth mass create heat consequentially slowing the rotation or some other effect?
    Last edited: Jul 31, 2009
  17. Jul 31, 2009 #16
    If I can spin an object on earth at 60 RPM and the only difference between it and an object 186,000 miles in circumference is size (I assume this is related to mass), why is the speed of light a limiting factor? Is it because of time slowing or the theoretical increase in mass? Both objects have the same rate of rotational velocity in the center. Only a small portion of the object would actually reach the speed of light. What does relativity say about a single object traveling at different velocities within itself?
    Last edited: Jul 31, 2009
  18. Jul 31, 2009 #17
    Is it possible that this twist/pull could be the cause of gravity? Sorry for so many questions, I'm sure this stuff is elementary to you guys.
  19. Jul 31, 2009 #18
    What about in the case of a black hole where the diameter is so small that the time differential is very minute. Does the twist unwind releasing all of it's energy or would this require a reversal of time?
  20. Jul 31, 2009 #19
    I wish I understood enough to give you any type of answer. I'm still not sure if anyone has confirmed whether time differential on a given object exists. Even if it does, i'm not sure if anyone has confirmed that a time differential within an object can cause mass to stretch or create any type of energy whatsoever.
  21. Jul 31, 2009 #20
    Do you think this makes some sense though or am I just babbling?
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook