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Does relativity have any day to day life applications?

  1. Nov 30, 2011 #1
    Can you use any of these theories in daily life? Or how can you?
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  3. Nov 30, 2011 #2
    Depends on your definition of "use" and also on who you are and what you do.

    If by "use" you mean that relativistic effects affect you or that you can directly observe or use the effects then the answer is yes.

    If by "use" you mean that an understanding of relativistic effects will help you achieve a goal then the answer depends on who you are and what you do. If you don't already know then you are probably a carpenter or attorney or something besides an engineer or scientist. In that case the answer is no. If you were an engineer or scientist then you would already know that the answer was yes.

    As for how, you need to pick your definition of "use" before I can answer that.
  4. Dec 1, 2011 #3


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    Every gps unit has to take relativity into consideration.
  5. Dec 1, 2011 #4


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    Magnetic fields exist because of relativity. So just about every electric machine you use depends on it.
  6. Dec 1, 2011 #5
    It depends on your 'daily life".

    Billions upon billions of people live and die without knowing anything about relativity. The very successful Roman legions didn't need it to conquer much of the known world. If a lion is chasing you on a savannah, relativity is a rather unimportant theory. And you don't need to know about it to watch TV or make popcorn.

    On the other hand, if you were thinking about trying to define absolute rest, or how fast information can be transmitted, or how relative speed or gravitational potential affect the passage of time, or how acceleration and gravity are similar, it could save you many years of effort.
  7. Dec 1, 2011 #6


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    There are also a lot of things you use , without thinking about it, that were designed by people who did understand relativity and used the theory of relativity when they were doing design. But you don't need to understand relativity to push the off/on switch.

    IT's rather interesting though, that people who claim to not believe in relativity don't usually seem to have any problem pushing the off on switch. They simultaneously claim the people who designed the device in question were wrong, while using the device in question (say, GPS) as if it were trustworthy, rather than regarding it as some faulty ill-designed bridge, liable to malfunction or fall down at any minute.
  8. Dec 1, 2011 #7


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    Yes, and we are fortunate to have different ways to know what time it is (and therefore what day it is) whether that be by getting time from a television, radio or internet broadcast, or from our cell phone, or from a GPS receiver, or even from a clock plugged into the wall, without the experts taking care of the details, it couldn't be done without them understanding relativity.
  9. Dec 1, 2011 #8
    Unless you are amish or an amazonian indigenous tribe the yes.
  10. Dec 2, 2011 #9
    By that definition even they depend on reletivity. Reletivity provides the fundamental speed limit of causality. Without this limit everything that has ever or will ever happen would have happened all at once. The universe would have been over at the big bang.
  11. Dec 3, 2011 #10
    Gold glows because of relativity
  12. Dec 7, 2011 #11
    TVs aren't built using CRTs anymore, but when they were, the electrons in the picture tube were accelerated to a sufficient percentage of the speed of light that the design engineers had to take relativistic effects into account, to ensure that the electron would hit the intended spot on the screen.
    Last edited: Dec 7, 2011
  13. Dec 7, 2011 #12
    Yeah, but the engineers didn't necessarily take it into account. It might help their understanding of electromagnetism, but that's it.

    The only major application I'm aware of for general relativity is GPS. Also, the orbits of bodies moving around the sun will have slight relativistic corrections, so I imagine that ought to have some practical significance for predicting the trajectories of asteroids and comets. That's rather important, since it is inevitable that one day the Earth will be hit by a big one, and we had better know as soon as possible.

    With special relativity, it's a different story. Lots of applications. One example would be nuclear physics. Nuclear power, nuclear weapons. Even in chemistry, you have to take relativity into account. Molecules may be moving very fast if the temperature is high. That means things have slightly more mass as they heat up. I'm sure there are many more. It's pretty far-reaching, actually, even though it's probably relatively rare overall in engineering that you can't get away with classical approximations.

    A full understanding of spin in quantum mechanics depends on relativity, and many other very fundamental things. The relativistic view of quantum mechanics is, of course, much more complete. And, even from the very beginning of quantum mechanics, starting with de Broglie, relativity played a role.


    So, you might be able to argue that any application of quantum mechanics is an application of relativity in that sense.
  14. Dec 12, 2011 #13
    Hm. Didn't know that. Sounds way to overcomplicated compared to now, although technology at the time of CRT TVs didn't allow for that, but still.
  15. Dec 13, 2011 #14
    The main reason which special relativity is taken into consideration in chemistry is not because molecules move very fast at very high temperatures (probably most molecules would dissociate before being accelerated to speeds comparable to that of light), but because inner electrons move very fast in heavy nuclei.

    In #10 I said that gold glows because of relativity; this is a typical relativistic quantum chemical effect.
  16. Dec 13, 2011 #15
    I may have said "very" fast, but it would be a mistake to interpret that as saying that they move near light speed. I didn't make that claim. The claim was just that they move faster, hence they have higher relativistic "mass".

    If I am wrong about this, it's my chemistry prof's fault, since this is essentially exactly what he told us. But at least I was right that relativity has a role in chemistry.
  17. Dec 13, 2011 #16
    Well, by «speeds comparable to that of light» I did not mean «near light speed», but speeds v<c for which special relativistic effects cannot be ignored. Notice that for v=0.05c typical terms as 1-(v/c)2 = 0.9975 ≠ 1 and relativistic corrections are relevant by the needed quantum chemical precision {*}

    As said, it is not needed to accelerate molecules to observe relativistic effects. They are already observed in the inner electrons of heavy atoms (as those of Gold) at rest.

    Some scientists continue using the old concept of relativistic mass, which varies with speed; however, the tendency in modern relativistic physics is to use invariant mass m≠m(v)

    {*} For high-precision computation, special relativity is not enough and QCD corrections are needed.
    Last edited: Dec 13, 2011
  18. Dec 13, 2011 #17
    Relativity seriously impacts my daily life. Without it, I would not have as many interesting educational videos to watch.
  19. Dec 13, 2011 #18
    Well, I was more or less aware of that. I wasn't saying it's normally needed in chemistry. It was my impression that it could come up, not that it's something that's normally necessary, and I was well aware it wouldn't be relevant in the vast majority of chemical situations.

    Somehow, I'm lazy about getting a sense for exact numbers and quantities, though. I don't know what kind of molecular velocities would ever come up normally in chemistry. But, let's say your gamma is 1.000001. If you have 1000 kilograms of stuff move at a speed giving you that gamma, you get that the relativistic mass increases by 1 gram. I'm no chemist, but it's conceivable that if you wanted a lot of precision in a high temperature kind of thing, maybe you would care. But I don't know.


    Actually, I was recently won over to the side of the invariant mass just a few days ago because of another thread here, the point being that the invariant mass is what is relevant for gravitational purposes. Up until then, I was never really sure which to use. I still think it helps to think of the other mass as an "apparent mass" in some situations.
  20. Dec 13, 2011 #19
    Good one. I don't know about videos, but any theory that is interesting enough and fun to learn about has a daily life application of just being fun in its own right.

    I can even impress women with my knowledge of physics on occasion. I told an ex about time dilation once and she seemed pretty surprised. I don't even know if she believed me or not. Short-lived relationship. Not much opportunity to follow up on it.
  21. Dec 14, 2011 #20
    I have two questions:

    (i) How many precision you think that we can measure mass? Hint look to the display of a modern high precision balance


    (ii) Did you read the note {*} in the message that you are replying?

    It is not true that the invariant mass «is relevant for gravitational purposes» only. When solving the Dirac equation in relativistic quantum chemistry and atomic physics, you must input the invariant mass of the electron.
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