-
Due to ongoing issues caused by Search, it has been temporarily disabled
-
You may need to edit your signatures. When we moved to Xenfora some of the signature options didn't come over. In the old software signatures were limited by a character limit, on Xenfora there are more options and there is a character number and number of lines limit. I've set maximum number of lines to 4 and unlimited characters.
Is light time dilated?
- Thread starter ynot
- Start date
CaveDave
Semicentenarian Troglodyte
From what I gather, anything traveling at c does not "experience" the passage of time, so I guess it would be dilated infinitely.
But, I may be talking totally out of my arse, too.
Cheers,
Dave
But, I may be talking totally out of my arse, too.
Cheers,
Dave
MetalPig
Illuminator
Same here. As far as I understand, photons don't age.
Keeps an eye out for the new L'Oreal Anti-Aging cream - "with added photons - because you're worth it".
Reality Check
Penultimate Amazing
Time dilated with respect an observer traveling at what velocity?
The basic answer is yes - light is dilated according to the velocity of the observer (relativistic Doppler effect).
Why should there be any problem with something that is time dilated travelling relative to an observer? Remember that the velocity of an object with respect to an observer is determined in the coordinate system of the observer - it's the rate of change in location (in observer's coordinates) vs. change in time (again, observer's coordinate time). It doesn't involve the object's proper time (the one that is dilated).
While that is true, travel at the speed of light is not necessary for that - electrons, for example, don't age either.
So it would be better to say that photons can't age - or more precisely, can't undergo spontaneous changes depending only on the time they have been travelling. (Note that they can and do undergo other changes - they interact with particles, they get redshifted as they travel through curved spacetime of the expanding universe, etc.)
Last edited:
Wouldn’t the travelling of the light itself be time dilated to the point that it would stop relative to the “proper time” of the observer? (if time stops at c)
ETA - I guess I’m asking that if relative motion causes time dilation wouldn’t that time dilation also dilate the very motion that causes the dilation?
Last edited:
Reality Check
Penultimate Amazing
No because light is not an observer.
Proper time is not dilated according to an observer travelling with the clock.
Superb response.
But I’m talking about light being observed by a “stationary” observer that light is travelling relative to at c. How can anything be observed to be moving at c (or any speed) if time stops at c?
Last edited:
Reality Check
Penultimate Amazing
I do not know what you mean by this.
All observers see light travelling at the speed of light even if they were to be travelling at the speed of light.
There is not such thing as a “stationary” observer -unless you state what they are stationary with respect to.
I believe Reality Check is saying that time dilation is defined as the relative rates as measured by two clocks in relative motion. Since no clock can be at rest in a photon's frame of reference it is not meaningful to speak of the rate at which time flows in a photon's frame of reference. If that's not what Reality Check is saying then it's what I'm saying.
Let’s agree for now that light is “special” and it’s speed isn’t effected by either relative motion or time dilation. But what about how time dilation effects the speed of material things moving relative to each other? Is the observed relative speed of all material things time dilated and their “actual” speed is faster than what is observed?
As I asked earlier - “If relative motion causes time dilation wouldn’t that time dilation also dilate the very motion that causes the dilation?” (discounting light).
As I asked earlier - “If relative motion causes time dilation wouldn’t that time dilation also dilate the very motion that causes the dilation?” (discounting light).
Reality Check
Penultimate Amazing
Time dilation does not case length contraction - it is caused by the relative velocity of the observers.
Thus time dialation will not "dilate the very motion that causes the dilation" if that is what you mean.
Let there be 2 observers Alice and Bob who have clocks. Bob is moving at a different velocity from Alice.
Alice will measure that Bob's clock is dilated (ticking slower).
Alice will measure that Bob's length is contracted.
Alice will measure Bob's velocity according to her reference frame, i.e. she will measure Bob's position at a point in time, measure Bob's position again to get his change in position and then divide by the amount of time that has passed. This velocity is not affected by her measurements of Bob's time dilation or length contraction.
sol invictus
Philosopher
- Joined
- Oct 21, 2007
- Messages
- 8,613
Let's make sure you've understood the basics. You set up a series of markers in your lab, spaced evenly a meter apart in a straight line. Then you stand nearby holding a timer as a clock whizzes by. You measure at what time the clock passes each marker (taking into account the time it takes its light to reach you), and dividing a meter by the time interval you measured gives its velocity in your rest frame.
When you do this you'll also notice the clock is running a bit slowly, and that it's a bit contracted in length. The degree of dilation and contraction is given by the relativistic gamma factor, as a function of the velocity you measured in the way I just described.
Now, is in some sense the velocity you measured a "dilated" version of the "real" velocity? Yes, I suppose so... you could think of the reason nothing can exceed the speed of light that way (the dilation gets arbitrarily large there, preventing any increase in the velocity you measure). But there's no need to think of things like that - the formula takes as its input the speed you measure, and it's much simpler to express things in those terms.
The answer is no, because a single photon or wave of light can't experience an event or anything else upon which to base a calibration of time. One of the implications of Special Relativity is that the word "time" doesn't really mean anything until you specify a context for the discussion, that is, a frame of reference within which an observer can exist. To be clear, it's OK for that observer to be purely theoretical, but you can't talk about how long something takes to happen, or whether any two events can be thought of as simultaneous, or when any event happened relative to any other event, until you know how fast your frame is moving relative to the other things around it. That is why it's called "The Theory of Relativity" in the first place.
Under normal conditions, things work the way Newton said they did. If you could go fast enough for relativistic effects to come into play, you would have to expend enormous amounts of energy to get to .9 times C, then .99, then .999. But at each point, the speed of light remains constant from your frame, light doesn't play by the same rules, and you can't get to C. You just can't, and forming a thought experiment that postulates that you can is beyond discussion, although perhaps not entirely beyond meaning. Einstein himself supposedly conducted that thought experiment many times.
So the best possible answer is that the behavior of time for a theoretical observer traveling along at the speed of light is undefined. For example, we know the light from the Sun takes around 8 minutes to get to us, but if we could ride that beam of light, would it take some brief number of seconds, or would it take no time at all and seem instantaneous?
No one knows the answer because there is no way to define or calibrate time in that context. Science doesn't have an answer. It's a mystery.
Under normal conditions, things work the way Newton said they did. If you could go fast enough for relativistic effects to come into play, you would have to expend enormous amounts of energy to get to .9 times C, then .99, then .999. But at each point, the speed of light remains constant from your frame, light doesn't play by the same rules, and you can't get to C. You just can't, and forming a thought experiment that postulates that you can is beyond discussion, although perhaps not entirely beyond meaning. Einstein himself supposedly conducted that thought experiment many times.
So the best possible answer is that the behavior of time for a theoretical observer traveling along at the speed of light is undefined. For example, we know the light from the Sun takes around 8 minutes to get to us, but if we could ride that beam of light, would it take some brief number of seconds, or would it take no time at all and seem instantaneous?
No one knows the answer because there is no way to define or calibrate time in that context. Science doesn't have an answer. It's a mystery.
Singularitarian
Banned
- Joined
- Jul 14, 2009
- Messages
- 1,007
Simply stated, the photon from its frame of reference does not experience time. According to relativity, this is because the speed it moves at has stretched time till it no longer experiences it pass. If we are to take relativity theory seriously, it then means that as a mathematical implication, it does not move through space either.
Now, conceptually understand that, and you can pretty much believe anything the relativistic theories provide.
Reality Check
Penultimate Amazing
Correctly stated, the photon from its frame of reference does "experience" time. According to relativity, this is because the photon is observing itself and thus its relative velocity is zero. Therefore the photon "experiences" no relativistic effects such as time dilation or length contraction.
Singularitarian
Banned
- Joined
- Jul 14, 2009
- Messages
- 1,007
What the heck are you on about?
A photon from its point of view does not experience time pass at all. In fact, it does't even have a proper existence at all. It's death and birth are simultaneously the same thing. It's internal experience is stuck in null trajectories, making the time dilation infinitely-stretched.
The photon has what’s called a 4-momentum [latex]p^{\mu}[/latex] and a 3-momentum [latex]P_i[/latex]. The photon in relativity
is said to move along a null trajectory so [latex]p^{\mu}p_{\mu}=0[/latex], but in considering the energy, traditionally given as [latex]E[/latex] and the 3-momentum this is [latex]-E^2+|p|^2=0[/latex]. The path it moves through space from
an observers point of view is completely different to that of a photons however. In usual metric structures, you have [latex]p^{\mu}p_{\mu}=-M^2=+E^2-(p^1)^2+p^{2}_{j}[/latex] with a perpendicular component given as [latex]j[/latex] in
this case.
Only from our perspective can a photon be seen to move through time.
A photon from its point of view does not experience time pass at all. In fact, it does't even have a proper existence at all. It's death and birth are simultaneously the same thing. It's internal experience is stuck in null trajectories, making the time dilation infinitely-stretched.
The photon has what’s called a 4-momentum [latex]p^{\mu}[/latex] and a 3-momentum [latex]P_i[/latex]. The photon in relativity
is said to move along a null trajectory so [latex]p^{\mu}p_{\mu}=0[/latex], but in considering the energy, traditionally given as [latex]E[/latex] and the 3-momentum this is [latex]-E^2+|p|^2=0[/latex]. The path it moves through space from
an observers point of view is completely different to that of a photons however. In usual metric structures, you have [latex]p^{\mu}p_{\mu}=-M^2=+E^2-(p^1)^2+p^{2}_{j}[/latex] with a perpendicular component given as [latex]j[/latex] in
this case.
Only from our perspective can a photon be seen to move through time.
Reality Check
Penultimate Amazing
What the heck are you on about?
The reason that I put "experience" in quotes is the obvious reason - a photon is not an observer and so it cannot experience time. Thus a photon has no point of view.
Now add an observer travelling with the photon. That observer does have a point of view. That observer experiences time passing as normal.
ETA
A photon also does not have a have a frame of reference as they are assigned by observers.
Last edited:
Singularitarian
Banned
- Joined
- Jul 14, 2009
- Messages
- 1,007
It's classed as a subatomic observer, it's still an observer. Just like the electron is a observing system, capable of decohering due to defining attributes with other particles. Like a spin-spin relationship, for instance. It just so happens as well, that particles experience time. The electron is even found to possess an internal clock.
But for the photon, it cannot move through time, because the Dilation has been stretched into infinity.
But for the photon, it cannot move through time, because the Dilation has been stretched into infinity.
Singularitarian
Banned
- Joined
- Jul 14, 2009
- Messages
- 1,007
And its impossible for inertial mass, like myself to travel at that speed. I contain rest mass, so my observation is pointless to imagine.
Reality Check
Penultimate Amazing
I am not sure what you mean by the last couple of posts.
But maybe you are talking about real observers such as you or me who cannot be accelerated to the speed of light.
However the observers used in relativity are theoretical observers. Their only property is the ability to observe. They can travel at the speed of light.
Dialtion is an observed effect.
An observer observing a clock travelling at the speed of light would measure that the clock has stopped. An observer travelling with the clock looking at a clock with the first observer would measure that the clock has stopped.
Thus your "Dilation has been stretched into infinity" statement means that time does not exist for either observer.
One observer is you. The other observer is attached to a photon.
Has time stopped for you?
Or to put it another way: A photon from its point of view sees that Dilation has been stretched into infinity for you since you are travelling at the speed of light relative to it. You cannot travel through time.
But maybe you are talking about real observers such as you or me who cannot be accelerated to the speed of light.
However the observers used in relativity are theoretical observers. Their only property is the ability to observe. They can travel at the speed of light.
Dialtion is an observed effect.
An observer observing a clock travelling at the speed of light would measure that the clock has stopped. An observer travelling with the clock looking at a clock with the first observer would measure that the clock has stopped.
Thus your "Dilation has been stretched into infinity" statement means that time does not exist for either observer.
One observer is you. The other observer is attached to a photon.
Has time stopped for you?
Or to put it another way: A photon from its point of view sees that Dilation has been stretched into infinity for you since you are travelling at the speed of light relative to it. You cannot travel through time.
Singularitarian
Banned
- Joined
- Jul 14, 2009
- Messages
- 1,007
Look - a photon cannot experience time pass.
That's a mathematical certainty.
That's a mathematical certainty.
Reality Check
Penultimate Amazing
Last edited:
edd
Master Poster
- Joined
- Nov 28, 2007
- Messages
- 2,120
How, then, can a photon have a frequency?
Singularitarian
Banned
- Joined
- Jul 14, 2009
- Messages
- 1,007
For crying out loud.
I do wonder sometimes about this place.
Quoted from Gribbin´s "Schrodinger´s kittens":
The Lorentz transformations tell us that time stands still for an object moving at the speed of light. From the point of view of the photon, of course, it is everything else that is rushing past at the speed of light. And under such extreme conditions, the Lorentz-Fitzgerald contraction reduces the distances between all objects to zero. You can either say that time does not exists for an electromagnetic wave, so that it is everywhere along its path (everywhere in the Universe) at once; or you can say the distance does not exist for an electromagnetic wave, so that it "touches" everything in the Universe at once. ''
I do wonder sometimes about this place.
Quoted from Gribbin´s "Schrodinger´s kittens":
The Lorentz transformations tell us that time stands still for an object moving at the speed of light. From the point of view of the photon, of course, it is everything else that is rushing past at the speed of light. And under such extreme conditions, the Lorentz-Fitzgerald contraction reduces the distances between all objects to zero. You can either say that time does not exists for an electromagnetic wave, so that it is everywhere along its path (everywhere in the Universe) at once; or you can say the distance does not exist for an electromagnetic wave, so that it "touches" everything in the Universe at once. ''
sol invictus
Philosopher
- Joined
- Oct 21, 2007
- Messages
- 8,613
Very strange, then, that (for example) the phase of a photon rotates as it travels, isn't it?
Last edited:
Singularitarian
Banned
- Joined
- Jul 14, 2009
- Messages
- 1,007
Strange as well that we observe a photon moving 150,000,000 km from the sun, but it's frame dictates there is no space to travel through.
As I understand it . . .
“travelling” things always experience their own “proper time” regardless of their relative speed. In other words a thing never experiences it’s own time dilation. Time dilation is the slowed rate of the “proper time” of a “travelling” thing relative to the “proper time” of a “stationary” thing and time dilation is only evident as a comparison of both “proper times“.
Light therefore wouldn’t experience any time dilation of it’s own “proper time” but would be time dilated to the point of 0 time relative to the “proper time” of everything else.
I don’t understand how time dilation wouldn’t dilate the very relative speed that creates it. I also think that everything in the Universe is moving/travelling in an absolute sense and don’t see how any relative movement/travel can be correctly defined as being either faster or slower that any other relative movement/travel
“travelling” things always experience their own “proper time” regardless of their relative speed. In other words a thing never experiences it’s own time dilation. Time dilation is the slowed rate of the “proper time” of a “travelling” thing relative to the “proper time” of a “stationary” thing and time dilation is only evident as a comparison of both “proper times“.
Light therefore wouldn’t experience any time dilation of it’s own “proper time” but would be time dilated to the point of 0 time relative to the “proper time” of everything else.
I don’t understand how time dilation wouldn’t dilate the very relative speed that creates it. I also think that everything in the Universe is moving/travelling in an absolute sense and don’t see how any relative movement/travel can be correctly defined as being either faster or slower that any other relative movement/travel
sol invictus
Philosopher
- Joined
- Oct 21, 2007
- Messages
- 8,613
It does, in a sense. For example, imagine a rocket accelerating at a constant rate in its own rest frame. To an observer, the apparent acceleration will get less and less as time passes and the rocket's speed approaches c.
Or is what you're confused about is some kind of infinite regression: velocity causes time dilation, but that reduces the velocity, which changes the time dilation, which changes the velocity... ?
If so, that's fully taken into account by the formula. It's like interest compounded continuously - there's interest on the interest on the interest ad infinitum, but the total is still finite, and we can write down a formula that takes all those corrections into account simultaneously. Math is powerful.
I can't figure out what you're confused about there. If motion is absolute, there's no problem defining relative velocity - just subtract the two absolute velocities. If it's not (and it isn't) there's still no problem.
infinitely dilated indeed.
Edit:
Also reading through these remember there is no ultimate frame of reference its always the observers frame, and light does not observe you, "dam light quit watching me at all stages of my life all at once dam you!"
Edit:
Also reading through these remember there is no ultimate frame of reference its always the observers frame, and light does not observe you, "dam light quit watching me at all stages of my life all at once dam you!"
Last edited:
So light is omnipresent all-seeing and all-knowing . . . Hmmmmmm.
bobdroege7
Illuminator
- Joined
- May 6, 2004
- Messages
- 4,162
Isn't the speed of light a theoretical maximum anyway, and doesn't matter bend light in essence slowing it down, so as long as there is one electron and one photon in the universe, that photon is slowed by the electron, no matter how far away the electron is?
Given there is no universal/absolute stationary I don’t see how relative velocities can be applied to things other than being universally/absolutely equal and opposite. If A is moving at x relative to B then B is also moving at x relative to A. Relative motion is motion between things not of things. Periods of acceleration doesn’t establish that anything is moving universally/absolutely faster or slower than anything else. Any time dilation that applies to a thing should apply equally to all other things that it moves relative to.
sol invictus
Philosopher
- Joined
- Oct 21, 2007
- Messages
- 8,613
They aren't, so long as you're considering only two objects or reference frames. But it's sometimes necessary to consider more than two.
You meant -x, but yes.
Yes.
Yes.
That's not quite how it works. Time dilation is an effect measured by some observer. That observer doesn't notice any time dilation of herself - only of something moving relative to her. Of course that thing would measure an equivalent time dilation of her - is that what you mean? - because as you say, the relative velocity is equal and opposite.
As far as I can tell everything you said is more or less correct, but you still seem to be confused by something...
Ziggurat
Penultimate Amazing
- Joined
- Jun 19, 2003
- Messages
- 59,064
Let's take a step back. Special relativity is all about the space-time metric:
ds2 = dx2 + dy2 + dz2 - (c dt)2To transform from one inertial reference frame to another, we must preserve ds2. The class of continuous transformations which do this are called Lorentz transformations. When we apply these transformations to an object, we can derive things like length contraction and time dilation, which are consequences of the Lorentz transformations. The Lorentz transformations are usually formulated in terms of a relative velocity between our initial reference frame and our final reference frame, and so are the length contraction and time dilation formulas. If we plug in c to our time dilation formula, it looks like time stops.
But we've actually skipped a step. What happens if we plug in c to our Lorentz transformations directly, and THEN see what we get? Well, we encounter a problem: if you try plugging in c for your relative velocities for the Lorentz transformations, you get a divide by zero. Which is undefined. So we cannot use the Lorentz transformations to change to a reference frame moving at the speed of light, and so the length contraction/time dilation equations derived from that are just not valid. Now, there are a number of ways of looking at that, but I think the simplest way to handle it is to simply conclude that a frame moving at c is not a valid inertial reference frame. This doesn't mean that nothing can move at c, it means that you cannot adopt it as a reference frame. So the question of what happens to time in the reference frame of the photon becomes meaningless.
Yes that is what I mean. But time dilation isn’t just an effect that is measured only by some single observer. If two observers are moving relative to each other they should both measure the same amount of time dilation of the other as you have agreed - “Of course that thing would measure an equivalent time dilation of her“. I can’t see that one observer might have undergone periods of accelerated to cause the relative movement is of any importance because as you have also agreed - “Periods of acceleration doesn’t establish that anything is moving universally/absolutely faster or slower than anything else”. I guess in my mind the only correct observation/measurement is a universal one that considers all observers simultaneously. This would create a paradox however with self-observed proper times conflicting with other-observed dilated times when they are in the same inertial frame.