4 ms·

Explain your last sentence ?

saagarjha 8y ago
From the frame of reference of each proton, the opposing proton is going nearly the speed of light. Edit: someone asked for a more detailed explanation, so here it is. Because of the equation in the article, it's impossible to see anything as moving faster than the speed of light in any reference frame; they just appear to asymptotically approach it. Both protons are moving at nearly the speed of light and perceive the other as moving at a speed that's slightly closer to the speed of light.
- deleted 8y ago
  [deleted]
AceJohnny2 8y ago
As an entity approaches the speed of light, its "timeframe" slows down. So the timeframe of one proton is slowed down so much that, to it, the speed of the incoming proton is only the speed of light. A key insight of Einstein's relativity is that the speed of time isn't fixed and absolute. Hence, "relativity". I highly recommend Chris Lee's excellent 2012 article on the history of "the speed of light" at Ars Technica: https://arstechnica.com/science/2012/09/the-complicated-truth-behind-scientific-findings/ https://arstechnica.com/science/2012/09/the-complicated-trut...
- jujulet 8y ago
  > speed of time isn't fixed and absolute Isn't 'speed' defined with the use of 'time'? Doesn't that make an expression such as 'speed of time' kind of meaningless?
  - saagarjha 8y ago
    This is "speed" in the sense of "how fast does time flow".
    - jujulet 8y ago
      Yeah but 'fast' is also defined in terms of time...
      - saagarjha 8y ago
        Exactly, it's a relative thing.
        jujulet 8y ago
        Maybe I'm missing something, but you're basically saying 'the speed of time is a function of the speed of time'.
        ablerman 8y ago
        Someone please correct me if I misunderstand, but it might be more useful to phrase it as, "the speed through time is a function of the speed through space"
        scottie_m 8y ago
        The whole point of relativity is that space and time are part of the same fabric: spacetime. Movement through both is relative, and inseparable. The Lorentz factor is a factor for distance, time, and mass.
        mikekchar 8y ago
        Even the word "movement" indicates this connection. You can not move if you have no time. And although it may be hard to imagine, the opposite is also true. Time doesn't really make any sense without space -- nothing can happen and therefore it can't take time. I am not a physicist, but I like to imagine that space actually created time. As soon as something separates from a singularity, you have time. It also makes me feel a lot more comfortable about quantum physics. Once you get smaller than a Lorenz wavelength, you don't really have space any more, just a probability that a particle may be somewhere and it magically teleports around. Well, you have to expect that, really, because if travel no distance, it can not (by definition) take any time. Probably not actually how things work, but it makes my brain happy anyway...
  - garmaine 8y ago
    No, the insight of Einstein is that speed (of light) is fixed and space and time are defined with respect to it. Is that weird? Yes. But that says more about our evolutionary instincts being off than anything else. Btw our atomic standard of length is defined with respect to the speed of light, making speed (he first derivative of space with respect to time) more fundamental than space itself. This isn’t just abstract theory.
    - jujulet 8y ago
      Ahh, I see. Thanks!
  - deleted 8y ago
    [deleted]
  - munchbunny 8y ago
    This is a mostly incorrect approximation of the concept, but I think the visual representation is useful. Think of an object's "velocity" as a unit vector in a 2d circle. X axis is fraction of C(meter/second), Y axis is rate of time passage (seconds/second). Every object no matter how slow moving has a velocity on the unit circle. An object that isn't moving is moving forward in time at the same rate as you, the observer. But an object that is moving very quickly moves much more slowly through time than you do as the observer. So the key distinction is that time is not a fixed reference, it's subjective depending on who is watching.
    - garmaine 8y ago
      This isn’t an incorrect approximation. It’s exactly how relativity was taught in my upper division physics class in college. General relativity basically starts with the assumption that everyone is moving through space-time at the speed of light. We sedentary material beings experience that mostly as moving through the dimension of time. Non material things like photons experience it as moving through space (because they lack inertia). When you accelerate to high speeds, you’re somewhere between the two extremes.
- noobermin 8y ago
  This may be a bit pedantic, but I don't like the framing "its 'timeframe' slows down" which is similar to an often used phrase "when you go close to the speed of light, your clock runs slower" because it gets the situation backwards and actually misses Einstein's key insight about relativity. The issue is in your own frame (say if you're a muon or a person), unless you're accelerating, you're at rest with respect to your frame. Physics after Einstein's special relativity assigns to each reference frame a way to measure spatial differences and times (cute terms used in textbooks are rulers and a clock). Now, if another object is moving wrt you at a fast speed that you measure that is close to c, when you measure things that happen to it, it appears to happen slower as measured by your clock. So the reality is it appears slower to you in your frame. An good example of this is a particle like a muon will appear to have a longer lifetime if it were moving relativistically (near c). The converse is (sort of) true: for the moving object, in its frame, when accounting for the distances traveled, your clock also appears slower to it. The reason framing it this way is important for me when I teach students is because it honors ones of the main points of special relativity that it did away with Newton's concept of a universal rest frame and made the important rest frame any inertial frame, and this helps demystify SR from being something esoteric but instead be based on simple logic: everyone is at rest in their own rest frame, so the physical laws in two frames moving respect to one another must be the same laws if you switch from one frame to the other. Since physics in any given rest frame seem to require light moves at c, certain other things must change in order to have both frames agree a light ray observed by both move at c.
- kian 8y ago
  Thank you for this!

From the frame of reference of each proton, the opposing proton is going nearly the speed of light. Edit: someone asked for a more detailed explanation, so here it is. Because of the equation in the article, it's impossible to see anything as moving faster than the speed of light in any reference frame; they just appear to asymptotically approach it. Both protons are moving at nearly the speed of light and perceive the other as moving at a speed that's slightly closer to the speed of light.

deleted 8y ago
[deleted]

AceJohnny2 8y ago

As an entity approaches the speed of light, its "timeframe" slows down. So the timeframe of one proton is slowed down so much that, to it, the speed of the incoming proton is only the speed of light. A key insight of Einstein's relativity is that the speed of time isn't fixed and absolute. Hence, "relativity". I highly recommend Chris Lee's excellent 2012 article on the history of "the speed of light" at Ars Technica: https://arstechnica.com/science/2012/09/the-complicated-truth-behind-scientific-findings/ https://arstechnica.com/science/2012/09/the-complicated-trut...

jujulet 8y ago
> speed of time isn't fixed and absolute Isn't 'speed' defined with the use of 'time'? Doesn't that make an expression such as 'speed of time' kind of meaningless?
- saagarjha 8y ago
  This is "speed" in the sense of "how fast does time flow".
  - jujulet 8y ago
    Yeah but 'fast' is also defined in terms of time...
    - saagarjha 8y ago
      Exactly, it's a relative thing.
      - jujulet 8y ago
        Maybe I'm missing something, but you're basically saying 'the speed of time is a function of the speed of time'.
        ablerman 8y ago
        Someone please correct me if I misunderstand, but it might be more useful to phrase it as, "the speed through time is a function of the speed through space"
        scottie_m 8y ago
        The whole point of relativity is that space and time are part of the same fabric: spacetime. Movement through both is relative, and inseparable. The Lorentz factor is a factor for distance, time, and mass.
        mikekchar 8y ago
        Even the word "movement" indicates this connection. You can not move if you have no time. And although it may be hard to imagine, the opposite is also true. Time doesn't really make any sense without space -- nothing can happen and therefore it can't take time. I am not a physicist, but I like to imagine that space actually created time. As soon as something separates from a singularity, you have time. It also makes me feel a lot more comfortable about quantum physics. Once you get smaller than a Lorenz wavelength, you don't really have space any more, just a probability that a particle may be somewhere and it magically teleports around. Well, you have to expect that, really, because if travel no distance, it can not (by definition) take any time. Probably not actually how things work, but it makes my brain happy anyway...
- garmaine 8y ago
  No, the insight of Einstein is that speed (of light) is fixed and space and time are defined with respect to it. Is that weird? Yes. But that says more about our evolutionary instincts being off than anything else. Btw our atomic standard of length is defined with respect to the speed of light, making speed (he first derivative of space with respect to time) more fundamental than space itself. This isn’t just abstract theory.
  - jujulet 8y ago
    Ahh, I see. Thanks!
- deleted 8y ago
  [deleted]
- munchbunny 8y ago
  This is a mostly incorrect approximation of the concept, but I think the visual representation is useful. Think of an object's "velocity" as a unit vector in a 2d circle. X axis is fraction of C(meter/second), Y axis is rate of time passage (seconds/second). Every object no matter how slow moving has a velocity on the unit circle. An object that isn't moving is moving forward in time at the same rate as you, the observer. But an object that is moving very quickly moves much more slowly through time than you do as the observer. So the key distinction is that time is not a fixed reference, it's subjective depending on who is watching.
  - garmaine 8y ago
    This isn’t an incorrect approximation. It’s exactly how relativity was taught in my upper division physics class in college. General relativity basically starts with the assumption that everyone is moving through space-time at the speed of light. We sedentary material beings experience that mostly as moving through the dimension of time. Non material things like photons experience it as moving through space (because they lack inertia). When you accelerate to high speeds, you’re somewhere between the two extremes.
noobermin 8y ago
This may be a bit pedantic, but I don't like the framing "its 'timeframe' slows down" which is similar to an often used phrase "when you go close to the speed of light, your clock runs slower" because it gets the situation backwards and actually misses Einstein's key insight about relativity. The issue is in your own frame (say if you're a muon or a person), unless you're accelerating, you're at rest with respect to your frame. Physics after Einstein's special relativity assigns to each reference frame a way to measure spatial differences and times (cute terms used in textbooks are rulers and a clock). Now, if another object is moving wrt you at a fast speed that you measure that is close to c, when you measure things that happen to it, it appears to happen slower as measured by your clock. So the reality is it appears slower to you in your frame. An good example of this is a particle like a muon will appear to have a longer lifetime if it were moving relativistically (near c). The converse is (sort of) true: for the moving object, in its frame, when accounting for the distances traveled, your clock also appears slower to it. The reason framing it this way is important for me when I teach students is because it honors ones of the main points of special relativity that it did away with Newton's concept of a universal rest frame and made the important rest frame any inertial frame, and this helps demystify SR from being something esoteric but instead be based on simple logic: everyone is at rest in their own rest frame, so the physical laws in two frames moving respect to one another must be the same laws if you switch from one frame to the other. Since physics in any given rest frame seem to require light moves at c, certain other things must change in order to have both frames agree a light ray observed by both move at c.
kian 8y ago
Thank you for this!