5 ms·

> 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 meaningl

> 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...
      - TallGuyShort 8y ago
        There are multiple references frames, and events can appear to be happening at different rates in different frames. So what you said actually does make sense because there are any number of references frames, each with their own view of how fast events are happening.
  - antonvs 8y ago
    The rate at which time passes is relative. You can in fact express this in terms of "seconds/second", as in how many seconds pass in some other reference frame for each second in yours. In that sense, the "speed of time" can in fact be meaningful. Relativity provides a more rigorous way of modeling this, treating spacetime as a four-dimensional manifold. When you move through the spatial dimensions relative to some reference frame, the rate of your motion through time is reduced relative to that same reference frame. This is commonly modeled on a spacetime diagram: https://en.wikipedia.org/wiki/Minkowski_diagram https://en.wikipedia.org/wiki/Minkowski_diagram
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.

> 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...
    - TallGuyShort 8y ago
      There are multiple references frames, and events can appear to be happening at different rates in different frames. So what you said actually does make sense because there are any number of references frames, each with their own view of how fast events are happening.
- antonvs 8y ago
  The rate at which time passes is relative. You can in fact express this in terms of "seconds/second", as in how many seconds pass in some other reference frame for each second in yours. In that sense, the "speed of time" can in fact be meaningful. Relativity provides a more rigorous way of modeling this, treating spacetime as a four-dimensional manifold. When you move through the spatial dimensions relative to some reference frame, the rate of your motion through time is reduced relative to that same reference frame. This is commonly modeled on a spacetime diagram: https://en.wikipedia.org/wiki/Minkowski_diagram https://en.wikipedia.org/wiki/Minkowski_diagram

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.