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Any in depth explanations on why near lightspeed affect aging?

  1. May 16, 2013 #1
    The time dilation effect on a lightclock moving horizontically is very easy to understand. But how does the speed affect our biological processes? "Because time slows down!" you might say. But specifically, what does make say the cells move slower? If they are moving in the same direction of a spaceship going really fast, then its logical to me that they'd get slowed down. But if the move in the opposite direction of that, surely they would travel quicker to a certain point in the body, thus eliminating the time dilation effect in this example?

    I was hoping that anybody could maybe explain how speeds this high specifically affects any biochemical process, similar to how the slowing of a clock is explained with the horizontically moving lightclock. Has anyone been able to explain this? I might be asking for the impossible here...

    P.S: I know that time isn't actually going slower or quicker per se. Time only moves quicker or slower in comparison to another point of reference, so that is not what is causing my confusion ;)
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  3. May 16, 2013 #2


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    Yes it is! :wink: Your biological processes do not slow down. In fact, all things in a moving spaceship behave exactly the same way as things in a ship that happens to be stationary. The slowdown is only an apparent effect, as observed by someone in a different reference frame.
  4. May 16, 2013 #3
    Let's consider an astronaut walking from the rear of a fast moving spaceship to the front of the spaceship, carrying a light clock, taking one step each time the light changes direction.

    The steps follow each other at slowed down pace, and the steps are lorentz contracted. So the astronaut proceeds really slowly. But luckily the spaceship is also lorentz contracted.

    When the walking direction is reversed, the light clock is tiny bit less slowed down, but the steps are not slightly less lorentz contracted (for whatever reason). So the astronaut proceeds a little bit faster in that diraction, but not according to himself, but according to us.
    Last edited: May 16, 2013
  5. May 16, 2013 #4


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    Somewhat simplified, SR says that there's simply "less time" along a path through spacetime that corresponds to a higher velocity. The theory tells us how to calculate the exact amount of time, but it doesn't explain why that formula holds.

    So your question is essentially "Why is SR a good theory?" This is a question that can't be answer by SR. It can only be answered by a better theory. Unfortunately the only better theory we have is GR, and everything I said about SR in the first paragraph is true about GR as well. So GR can't answer this either.
  6. May 16, 2013 #5


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    Have you never read even an introductory book on relativity? There is NOTHING that makes "biological processes" in particular slow down. All that happens is that time (as observed from a stationary frame of refrence) slows down. As far a the person in whom those "biological processes" are occuring is concerned there is no slowing down. It is only from the viewpoint of a person, with respect to whom he is moving very rapidly, that he has slowed down. And from his point of view, that person has slowed down, not him.
  7. May 16, 2013 #6


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    I'm not sure where the disjoint in your thinking is.

    First lets consider a light clock, next to a wide variety of clocks. In the mechanical clock section, one clock has a balance wheel, another has a tuning fork, and a third is a quartz crystal. Then we have a chemical clock, based on how fast some particular chemical reaction occurs. And one based on radioactive decay. And add in as many more types of clocks as you want to put in.

    If you can detect any difference between ANY of those clocks and the light clock, the principle of relativity is not satisfied. You can detect 'absolute motion', just by comparing that particular clock to a light clock.

    So the point of relativity isn't that "light clocks" slow down. All clocks slow down. If they didn't, we'd be able to detect when we were moving. There would be something "different" about the laws of physics of moving object than ones that were not moving.

    It happens to be more obvious that the clock must slow down in the light clock, but once one sort of clock slows down, the idea that the laws of physics are the same in all reference frames implies that all sorts of clocks must slow down.

    Biology isn't any different (from a scientific point of view) than any of the other clocks. I'd say it was most similar to the one based on chemical reactions.
  8. May 16, 2013 #7
    You have to keep in mind that observers in neither frame can be said to be the ones moving. All that can be said is that they measure processes occuring in the moving frame are going slower when compared to the same process going on in their, rest, frame. Make a dozen clocks of different construction and make one light clock. Let them all tick at the same rate and adjust that rate to be the rate of the average human heart beat when at rest. Then observers in a frame moving relative to yours reckon that all those clocks slowed down and are keeping pace with each other.
  9. May 19, 2013 #8
    Relativity which says that Time Dilation is relative,says that we cannot use or think it as a time travel to the future. I have seen many videos which says that Time Dilation can be used to stay younger than the others... We can find that those videos are not right.. Because Time Dilation is relative.
  10. May 19, 2013 #9
    How can two identical clocks separate, take different paths, and have different elapsed times when compared, if it's only apparent? the Haefele-Keating experiment is a specific case.
  11. May 19, 2013 #10


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    I think you might be confusing time dilation ( a coordinate effect ) with differential ageing - which is coordinate independent. The time accumulated between two events along a clocks worldline is invariant and is a property of the worldline. This is the twin paradox.
  12. May 20, 2013 #11
    Oh.. differential ageing is coordinate independent.. ok..
  13. May 20, 2013 #12


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    From the definition of proper time ( with c = 1 )

    ##d\tau^2= dt^2 -dx^2 - dy^2 - dz^2##

    If we make the transformation

    ##t = \gamma t' + \beta\gamma x', \ \ x = \gamma x' + \beta\gamma t',\ \ y'=y,\ \ z=z'## we can get the transformed differentials

    ##dt = \gamma dt' + \beta\gamma dx', \ \ dx = \gamma dx' + \beta\gamma dt',\ \ dz=dz',\ \ dy = dy'##

    and substituting these into the first equation we get

    ##d\tau^2= dt^2 -dx^2 - dy^2 - dz^2= dt'^2 -dx'^2 - dy'^2 - dz'^2##
  14. May 22, 2013 #13
    Hey,and i know proper time is invariant in SR.. Why did you prove it to me?
  15. May 22, 2013 #14


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    I know what you mean, but I think that that way of putting is misleading, because it makes it seem that time dilation is an illusion and is not real. But there are time-dilation effects that are objective and not observer-dependent. If a traveler starts at point A and travels to point B, the amount of aging along the trip will depend on the velocity profile along the trip. That's not just an apparent effect.
  16. May 22, 2013 #15


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    Yes, that's why it's useful to differentiate between "time dilation" and "differential aging".
  17. May 22, 2013 #16


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    Sure, but I think people can be confused by that, as well. If you think of time dilation as an "illusion" of some sort, but differential aging as "real", it's a little weird that the time dilation formula gives you exactly the correct amount of differential aging for two travelers.

    I think it's not completely correct to say that time dilation is "apparent". It's relative to a coordinate system, but it's not an illusion.
  18. May 22, 2013 #17
    Well, I'm sorry for phrasing it wrong. Yes, I have read an introductory book on relativity. The biological processes do in fact slow down upon travel near lightspeed, in comparison (!) to a stationary frame of reference. I'm talking about a scenario similar to the twin paradox.
  19. May 22, 2013 #18
    Hey, I think that you misunderstood my question. I know that any type of clock (even biological) would slow down just as much as a light clock when moving near light speed, in comparison to a stationary frame of reference. I was merely wondering what the mechanical (hopefully the right word) aspect of it would look like, which is so beutifully depicted with the light clock. I would claim that I do understand and accept relativity and time dilation, I would just like to explore the some scenarious deeper, asking myself "How does it work?". If you respond "because time slows down" I think I'll start crying.. I know time slows down! xD
  20. May 22, 2013 #19
    Hey! Thank you for a humble answer. This sort of confirms what I thought, that it is very hard to explain mechanically or biochemically why everything relatively slows down due to high speeds. That is, however, not to say that we can't prove relativity as a fact (for example the slowed down decay of muons). So, I definetely don't doubt that SR is a good theory, or an accurate one for that matter.
  21. May 22, 2013 #20


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    It's the fact that the laws of physics (including chemistry and any other laws you can think of) remain unchanged when processed through the Lorentz Transformation. This was a major significance of Einstein's contribution in his theory of Special Relativity. Prior to Einstein, some laws transformed unchanged using the Lorentz Transformation and others transformed unchanged using the Galilean Transformation. Of course, this incompatibility only worked at slow speeds and with low resolution but eventually, all the laws that followed the Galilean Transformation had to be modified so that they would no longer follow the Galilean Transformation but would instead follow the Lorentz Transformation. Once we bring all laws into conformance with the Lorentz Transformation, we are guaranteed, without looking at the details, that all processes, biological, mechanical, optical, etc. will exhibit the same time-related consequences.

    Of course, if you wanted to, you could look into the details of some complicated biological process in a particular rest frame and then transform all the coordinates of significant events into another frame moving at high speed and you would find that everything compares identically to the results of a light clock. But once you do it for a light clock and a few other simple scenarios, you just realize that it will work the same for complex scenarios and so the mystery goes out of the issue and the motivation to work out the details in the complex situations evaporates.
  22. May 22, 2013 #21


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    That's one way of looking at it. Another is that clocks don't slow down due to high speeds. They just keep doing what they always do, which is to indicate the proper time of their world lines (the curves in spacetime that describe their motion). This is the most natural interpretation of relativity. If we stick to it, it doesn't make sense to ask what process is effecting the final ages of the the twins in the twin paradox. If they had any other ages, that would have required explanation.

    The idea that clocks actually slow down is a less natural interpretation of relativity, inspired by human intuition and the old ether theory. If we adhere to this interpretation, then it's natural to blame the slowing of clocks on their interaction with the ether as they move through it.

    I recommend that you don't think about clocks in this way (because there's zero evidence for the existence of an ether), and instead try to understand the concept of proper time.
  23. May 23, 2013 #22
    Hi Viktor.....

    THAT is your answer. The clock you carry along your journey [Fredrik describes it as your 'worldline'] records your proper time at a steady, unchanging tick tock tick tock. What other people may see is their problem, not yours. After all, you see their clocks ticking differently than your clock.

    Fredrik's explanation says it all.....

    Here is an analogy: When you stand next to, say, a house and it seems so big to you while at the same time your friend looks at it from a mile away and it looks so small, and so do you, how can that be??

    You don't even think that way because it is an 'illusion', a 'paradox', you are used to....You can resolve it mathematically by comparing the tangents of your viewing angles....you can estimate different observational heights based on observer distances from the object....

    [In fact sailors use such an approach to determine their distance offshore.....when they know the actual height of an object [always provided on US NOAA navigation charts]. No mystery.

    As Fredrik suggests, different ways of thinking make things easier: So when I think about relativity of time, I always keep in mind the two things that affect the relative passage of time: relative speed [in SR] and gravitational potential [in GR]. And since time and space conspire to keep the speed of light a constant, c, that quick memory device also tells me that those two factors must affect distance [length] as well.
    Last edited: May 23, 2013
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