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LiquidBleach
2018-Mar-19, 07:20 PM
hi....ive often thought light was the fastest thing....but then one day thinking it popped into my head the question, is maybe time faster than light...or does time have no speed at all?

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Ken G
2018-Mar-19, 07:45 PM
Normally we think of speed as a rate of change of distance, i.e., distance divided by time. In this way of thinking, the speed of time could only be regarded as unity, i.e., one second per second. It is often useful to measure distance in time units by using the speed of light (the concept behind a "light year"), and when you do that, the speed of light is also unity (one light year per year). So in this sense, we can reasonably say that the speed of light, and the speed of time, are the same. Indeed, this is the central idea of unifying space and time into a "spacetime manifold."

swampyankee
2018-Mar-19, 08:26 PM
Speed or velocity is distance divided by a time; assigning a velocity to it [time] is not valid

LiquidBleach
2018-Mar-19, 08:28 PM
Normally we think of speed as a rate of change of distance, i.e., distance divided by time. In this way of thinking, the speed of time could only be regarded as unity, i.e., one second per second. It is often useful to measure distance in time units by using the speed of light (the concept behind a "light year"), and when you do that, the speed of light is also unity (one light year per year). So in this sense, we can reasonably say that the speed of light, and the speed of time, are the same. Indeed, this is the central idea of unifying space and time into a "spacetime manifold."interesting, I hadn't thought of it like that. does the same rules apply to anything that is not moving? when I stand still, time still, time still passes....maybe the distance comes in that I can't go backwards in time...it is constantly only moving in one direction. sorry if my questions are trivial but the answers help quench a curious mind.

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LiquidBleach
2018-Mar-19, 09:04 PM
Normally we think of speed as a rate of change of distance, i.e., distance divided by time. In this way of thinking, the speed of time could only be regarded as unity, i.e., one second per second. It is often useful to measure distance in time units by using the speed of light (the concept behind a "light year"), and when you do that, the speed of light is also unity (one light year per year). So in this sense, we can reasonably say that the speed of light, and the speed of time, are the same. Indeed, this is the central idea of unifying space and time into a "spacetime manifold."time then is a constant, not having speed at all then but used or "put together" with other things to fill in a value in an equation... sorry if what I say is trivial, I only have minimal education but I have a very curious mind.

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Swift
2018-Mar-19, 09:14 PM
interesting, I hadn't thought of it like that. does the same rules apply to anything that is not moving? when I stand still, time still, time still passes....maybe the distance comes in that I can't go backwards in time...it is constantly only moving in one direction. sorry if my questions are trivial but the answers help quench a curious mind.

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Even if you are standing still, things are still happening; things that happen over time. There are chemical reactions in your body (even in a dead body). If there are radioactive nuclei in your body, they are still waiting to decay. The electrons in their orbitals around their atoms are moving around. Photons are hitting your body and are either being absorbed or reflected.

And all of this is true whether you are a non-moving person, or a non-moving rock.

PetersCreek
2018-Mar-19, 09:21 PM
interesting, I hadn't thought of it like that. does the same rules apply to anything that is not moving? when I stand still, time still, time still passes....maybe the distance comes in that I can't go backwards in time...it is constantly only moving in one direction. sorry if my questions are trivial but the answers help quench a curious mind.

Think of it this way: we can only describe an object's position in space using three dimensions. To describe an object's movement through space, you need to use the fourth dimension of time. It isn't really meaningful to say that time is faster or slower than light just like it doesn't make sense to say that distance is faster or slower than light. It's the light, the space ship, the turtle, or the hare that are moving. The dimensions are our yardsticks and stop watches.

Ken G
2018-Mar-20, 02:36 AM
interesting, I hadn't thought of it like that. does the same rules apply to anything that is not moving? when I stand still, time still, time still passes....What is often said is that you always move entirely through time, at the rate 1 second per second, and not at all through space, because that is your perspective. Light, from your perspective, does the opposite-- it moves entirely through space, at the rate of 1 "light second" per second. Objects that are in motion, with respect to you, at speeds less than c move through time and space in some kind of combination of the two, hence you regard them as time dilated as well as moving.

cosmocrazy
2018-Mar-20, 10:39 AM
What is often said is that you always move entirely through time, at the rate 1 second per second, and not at all through space, because that is your perspective. Light, from your perspective, does the opposite-- it moves entirely through space, at the rate of 1 "light second" per second. Objects that are in motion, with respect to you, at speeds less than c move through time and space in some kind of combination of the two, hence you regard them as time dilated as well as moving.

What I find fascinating is that from the perspective of the light (a photon) no time or distance passes. So would it be fair to say that time emerges from the existence of mass and that the rate/speed at which it passes is gravity and speed dependent relative to reference frames ?

John Mendenhall
2018-Mar-20, 12:28 PM
What I find fascinating is that from the perspective of the light (a photon) no time or distance passes. So would it be fair to say that time emerges from the existence of mass and that the rate/speed at which it passes is gravity and speed dependent relative to reference frames ?

I don't think time is emergent from mass.

Ken G
2018-Mar-20, 12:35 PM
What I find fascinating is that from the perspective of the light (a photon) no time or distance passes. So would it be fair to say that time emerges from the existence of mass and that the rate/speed at which it passes is gravity and speed dependent relative to reference frames ?I don't think so. The frame of a photon itself is regarded as singular, but you can see what is happening by simply taking the limit of a particle with less and less mass going closer and closer to c. What you find is that nothing strange happens with the passing of time-- all the particles in that series experience the passing of time completely normally. It only appears that the time they experience is getting shorter if we fix some time interval in our own frame, but there's no reason to do that if we are interested in what is happening to those particles, because none of those particles care what we regard as a fixed interval of time. What does happen for that series of particles is that lengths across the galaxy get length contracted, so matter gets quite a bit denser in the direction the particle sees the masses as moving. At some point in that series, everything we regard as the observable universe gets contracted into a single meter of distance, so of course the particle traverses that distance almost instantly. But that doesn't mean time isn't passing, because for all we know the universe is infinite in size so there's plenty more universe to traverse even as we take the limit of that series. So what all this suggests to me is that proper time is just proper time, and there is no sense to which the rate that proper time is passing does anything as we consider faster and faster particles-- it's always one second per second, so that holds even in the limit.

cosmocrazy
2018-Mar-20, 01:06 PM
I don't think so. The frame of a photon itself is regarded as singular, but you can see what is happening by simply taking the limit of a particle with less and less mass going closer and closer to c. What you find is that nothing strange happens with the passing of time-- all the particles in that series experience the passing of time completely normally. It only appears that the time they experience is getting shorter if we fix some time interval in our own frame, but there's no reason to do that if we are interested in what is happening to those particles, because none of those particles care what we regard as a fixed interval of time. What does happen for that series of particles is that lengths across the galaxy get length contracted, so matter gets quite a bit denser in the direction the particle sees the masses as moving. At some point in that series, everything we regard as the observable universe gets contracted into a single meter of distance, so of course the particle traverses that distance almost instantly. But that doesn't mean time isn't passing, because for all we know the universe is infinite in size so there's plenty more universe to traverse even as we take the limit of that series. So what all this suggests to me is that proper time is just proper time, and there is no sense to which the rate that proper time is passing does anything as we consider faster and faster particles-- it's always one second per second, so that holds even in the limit.

This is the part I'm confused about (my bold). From the perspective of a particle travelling at C space is contracted to zero, time is dilated to zero. So time and space become meaningless from the particles perspective, or does the particle experience time as if it were in suspended animation?
If space is contracted to zero then how does this relate to a universe which is infinite in size (space).

cosmocrazy
2018-Mar-20, 01:19 PM
What I have read is this

"There is no such thing as a “lack of time flow at c”. This is a common misunderstanding, which arises when people try to extend the laws of SR outside its domain of applicability. A photon is not a valid frame of reference, and neither is any other particle with zero rest mass, so asking what time a clock co-moving with a photon would record, is physically meaningless, since no clock can move at c. However, the world line of a photon in spacetime still has a well defined geometric length, but to find it you need to parametrise the world line with something other than proper time. When you do this for (e.g.) a photon going from the sun to the Earth, you will find that this world line has a length of approx eight light minutes, and all observers agree on this (geometric world line lengths are relativistic invariants)."


This sort of clears it up some for me.

Ken G
2018-Mar-20, 02:19 PM
This is the part I'm confused about (my bold). From the perspective of a particle travelling at C space is contracted to zero, time is dilated to zero. Actually, it is what you and I regard in our reference frame as a finite time and distance that are contracted to zero for the photon, but we don't know there is not infinite space and infinite time. So it's a bit like the ratio x*(1/x) as x goes to zero. If you only consider the first number, it looks like you should get zero, but if you consider both numbers, and if you take the limit as x gets smaller and smaller, the ratio is always 1. It's pretty reasonable to attribute a limiting value of 1 to a series of numbers that are always 1 everywhere in the series.


So time and space become meaningless from the particles perspective, or does the particle experience time as if it were in suspended animation? The latter is what is not supported by that limiting series I'm talking about. The former does create a problem, because throughout the series, distances between galaxies are getting shorter and shorter until it's not clear what you have there. The density of matter observed by the fast particle is reaching a kind of singularity, as are some other aspects explained in another current thread by grant hutchison about what you see as you approach c. So the frame of a photon is clearly a singular frame and should probably be avoided by observers, but one can still imagine a series of faster and faster observers, and throughout that series the one thing that stays the same is that nobody gets any closer to being in "suspended animation"-- proper time is just proper time for all of them.

If space is contracted to zero then how does this relate to a universe which is infinite in size (space).
Exactly the point.

Ken G
2018-Mar-20, 02:40 PM
"There is no such thing as a “lack of time flow at c”. This is a common misunderstanding, which arises when people try to extend the laws of SR outside its domain of applicability. A photon is not a valid frame of reference, and neither is any other particle with zero rest mass, so asking what time a clock co-moving with a photon would record, is physically meaningless, since no clock can move at c. However, the world line of a photon in spacetime still has a well defined geometric length, but to find it you need to parametrise the world line with something other than proper time. When you do this for (e.g.) a photon going from the sun to the Earth, you will find that this world line has a length of approx eight light minutes, and all observers agree on this (geometric world line lengths are relativistic invariants)."I've also heard about parametrizing world lines in ways other than proper time, but I haven't heard of "geometric world line length," and I'd be interested in hearing more about how that is determined (it sounds like a distance between world lines of objects in the same frame, as reckoned in that frame, but I suspect it encounters difficulties in general relativity). But it doesn't particularly matter to me if there are other ways to find invariant lengths along a curve, as proper time is the one that we are actually talking about (in terms of the experience of the observer following that world line). To me the issue is, what are we keeping fixed as we consider world lines that are closer and closer to the light cone.

The approach you are taking is to keep fixed a time as perceived in your coordinates, and then you get that the proper time along this series of curves is less and less. But another approach is to keep the proper times along the curves fixed, and then the world lines simply cover more and more distance and time in your reference frame as they get closer to the light cone. So taking this latter approach, the singularity you approach is not a shortening of the amount of time the observers experience until it gets to zero, it is an increase without bound in the number of galaxies the observer passes in a given amount of their own proper time.

I argue that this latter approach is what we would use if we could really build spaceships that travel at close to c. So I don't think we would say that astronauts in those spaceships are nearing a state of suspended animation, though people who like the concept of "time dilation" might indeed imagine that. Instead, I think we would say that our astronauts simply have a greater range that they can travel in their lifetimes. Proceeding to the limit of a photon then means the range increases without bound. If the photon eventually hits something and is destroyed, then it can't reach its potential range, and it would never experience any time elapsed, but not because it was in suspended animation-- it would just get a zero lifetime, just as our hypothetical astronauts in near-c ships would get a very short lifetime if their ships hit a star before they even got out of our galaxy.

Someone who gets a short lifetime is not said to have time passing more slowly, they just get less time before their life ends. It's all a question of what are you holding fixed whenever you make a comparison. But if we do fix the distance covered, for example by saying we have particles emitted at given point A and absorbed at given point B, then we can take the limit of faster and faster speeds and get shorter and shorter proper times. But even then, in the same vein as "astronaut lifetimes," I would say that in the limit of photons, we just have a lifetime of zero time in their own frame (a concept supported by taking a limit of faster and faster particles), not that they were ever in suspended animation or that time ever stopped for them. There's a big difference between having time stop, and just not getting any time because something else happened right away. That's something we can relate to in personal experience!

cosmocrazy
2018-Mar-21, 06:44 AM
Thanks Ken, I see your point and it makes better sense to me than what I had previously imagined.

borman
2018-Mar-24, 05:30 PM
While the speed of light is the speed limit within space-time, space-time itself can expand faster than light. This would give the appearance that distant galaxies slow their rotation rate and get dimmer and eventually fade away behind the horizon. This is not because light is slowing down but because space-time is expanding faster than the speed of light.