Linked Questions
61 questions linked to/from Does a photon in vacuum have a rest frame?
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Photons moving relative to photons [duplicate]
I know we can't move at the speed of light, but if we were to travel on a photon how fast would we see other photons going? The speed of light is constant... So do photons see other photons moving at ...
user24082
4
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1
answer
940
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How can a photon "stop"? What does its world line look like? [duplicate]
Einstein famously made a thought experiment: what would he see if he sat on a beam of light? His answer was -- it's impossible. Owing to him being a body with mass, he can never ever reach light speed ...
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4
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Photon Emission/Absorbsion from the Photons Perspective [duplicate]
First some assumptions.
1) Photons travel at the speed of light.
2) From the photon's reference spacetime is contracted to 0 length in the direction of photon travel.
3) From the photon's reference ...
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2
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2
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Why isn't it valid to consider a photon at rest with everything else moving at $c$? [duplicate]
Since relativity postulates that the laws of physics are invariant in all inertial systems, why can't photons have an inertial reference frame?
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3
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Does a photon not having a reference frame result in logical inconsistency? [duplicate]
So, I know that SR makes two statements.
One is the first assumption it has:
"Speed of light is the same with respect to all reference frames".
Second, the statement:
"A photon cannot have a ...
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4
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762
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Does light in vacuum actually travel at the speed of light? [duplicate]
I know my question sounds like a joke (and I suppose on some level it is) but I'm confounded by the following:
As the thought experiment goes, if I'm in a spaceship flying rapidly the people on earth ...
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1
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According to Einstein & Brian Greene, does the photon remain stationary in the fourth dimension? [duplicate]
According to Einstein and Brian Greene, does it logically follow that the photon remains stationary in the fourth dimension?
In An Elegant Universe, Brian Greene writes:
“Einstein found that ...
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3
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Are photon rest frames distinguishable from other inertial frames? [duplicate]
The principle of relativity suggests that all inertial frames are indistinguishable. But if I consider the rest frame of a photon (i.e. an IRF traveling at speed $c$ w.r.t. me), then won't it be ...
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2
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2
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366
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Is it possible for a photon to be at rest? [duplicate]
I know it doesn't really make sense if looking at the photon from the wave point of view, but is there any law of physics which prohibits a photon from stopping completely? Thanks.
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2
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How can photon have wave properties if they travel at the speed of light? [duplicate]
I am not a physicist so please excuse me if this is a dumb question.
As far as I understand Relativity, as observer (in this case a photon) travels at the speed of light, time stops. So how can the ...
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3
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930
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From the photons perspective [duplicate]
Probably been answered but couldn't find the answer.
From the perspective of a photon:
- For the photon to travel from body A to body B would take 0 secs.
- The universe would be one point in "...
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1
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488
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What is the velocity of a photon with respect to another one? [duplicate]
When light comes from a source, there are numerous photons associated with the energy packets.
Now, what is the velocity of a single photon with respect to another photon coming form the same source i....
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1
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562
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Can a frame of reference travel with the speed of light? [duplicate]
I read that nothing with mass can travel at the speed of light. Therefor one can not ask what happens when an observer in a car moves with the speed of light. But, is it possible for a frame of ...
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2
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If a massless observer is going at the speed of light, what speed will it measure of a light beam going parallel to it? [duplicate]
If a massless observer is going at the speed of light, what speed will it measure of a light beam going parallel to it?
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1
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158
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Do photons exist from point of view of photon? [duplicate]
If photons are travelling with speed of light, it means that time is stopped for photons and there is no any distance in the Universe for them. So, does it mean that photons do not exist? From the ...
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1
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What is the speed of one photon of a beam of light with respect to the other photon of the same beam? [duplicate]
as according to special relativity the relative speed is $u'=\frac{(u-v)}{1-(uv)/c^2}=\frac{0}{0}$ because $v=c$ the speed of second photon with respect to any inertial observer and $u=c$ speed of ...
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1
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Observers at the speed of light [duplicate]
Just a quick question to help me see if my reasoning is right. The speed of light is constant from all frames of reference. So does this mean that an observer travelling at the speed and taking into ...
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1
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149
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Why aren't we all moving at the speed of light relative to photons? [duplicate]
Using basic logic.... We know speed and velocity is relative. My point is if we take our speed with respect to a photon moving in opposite direction we are practically moving at speed greater than ...
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1
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102
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How many quanta can travel at light speed relative to each other simultaneously? [duplicate]
How many quanta can travel at light speed relative to each other simultaneously?
I know the concept of being "simultaneous" breaks down at a distance so let's assume for the sake of ...
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1
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0
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81
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Light at the Speed of Light [duplicate]
Since light particles travel at the speed of light, we know it's possible for something to travel at that speed. However, since all things are relative, and if time does stop at the speed of light, ...
user108794
1
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1
answer
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Implication of Relativity [duplicate]
According to relativity, no useful matter can travel faster than light. Suppose that your are a light beam travelling. Now you have a parallel light beam travelling beside you. Suppose you look at the ...
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1
answer
75
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What is speedlight travel "really" like (for a photon)? [duplicate]
To begin with, I'm clearly not a physicist but I'm certainly interested by several physics questioning.
So, my question here is, according to Einstein's relativity, I understood that travelling at the ...
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2
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Spacetime in photon frame [duplicate]
The time-axis and the space-axis overlap for a photon's world line. Does it mean that photon has no "past" or "future" but only "present" and no "there" but ...
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1
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Do photons move from their point of view? [duplicate]
If at light speed time doesnt exist do photons not move from their point of view? If they dont, what would happen if you took a photon and somehow stopped it would it be at the same point at its POV ...
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4
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130
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Photons confuse me [duplicate]
I'm not entirely sure if my question is valid or not but I'll ask it anyway. So my physics porf. told us the Photons are constantly in motion and they never come at rest and the sub-topics relating to ...
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Reference frame for massless particles like light [duplicate]
One of the axioms of special relativity is that the speed of a massless "particle" such as light is c in all reference frames. In this comment from another question, The reference frame of $c$, ...
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0
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Is any photon really moving? [duplicate]
I read that when something moves at the speed of light, length contracts at the direction of motion. Now consider a photon traveling in the z axis. Since it is travelling at the speed of light, the z ...
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0
answers
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Would it be ok to say that not all light travels at the same speed when you consider its own perspective? [duplicate]
The reason I am asking is because higher energy would cause greater gravitational time dilation. Therefore I would expect, from the perspective of a radio wave, a gamma ray having more energy would ...
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10
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Would time freeze if you could travel at the speed of light?
I read with interest about Einstein's Theory of Relativity and his proposition about the speed of light being the universal speed limit.
So, if I were to travel in a spacecraft at (practically) the ...
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3
answers
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What are galactic speeds measured against?
The Earth moves through space at 67,000 MPH. The Milky Way travels through a local group at 2,237,000 MPH.
Wouldn't you need a fixed point to be able to measure velocity against? After all, compared ...
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5
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How do electromagnetic waves travel in a vacuum?
This is perhaps a total newbie question, and I will try to formulate it the best I can, so here it goes. How does an electromagnetic wave travel through for example, the vacuum of space?
I usually ...
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3
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Do we move at the speed of light relative to light?
My understanding of relativity isn't very sophisticated, but it seems to me that relative to a photon moving at the speed of light, we are moving at the speed of light. Is this the case?
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7
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What is $c + (-c)$?
If object A is moving at velocity $v$ (normalized so that $c=1$) relative to a ground observer emits object B at velocity $w$ relative to A, the velocity of B relative to the ground observer is
$$ v \...
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6
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Why do photons travel?
Photons travel at the speed of light.
Is there a known explanation of this phenomenon, and if yes, what is it?
Edit:
To be clearer, my question is why do photons travel at all. Why do they have a ...
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6
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1
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Frame of reference of the photon? [duplicate]
In the frame of photon does time stop in the meaning that past future and present all happen together?
If we have something with multiple outcomes which is realized viewed from such frame? Are all ...
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1
answer
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Why can't we make measurements in a photon's rest frame when loop diagrams make measurements possible?
It is one of the axioms of special relativity that the photon has no rest frame; light travels at speed c when measured in any inertial frame of reference. As a corollary, it is often said that if one ...
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3
answers
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I have an issue with how long sunlight takes to reach Earth
It is a well-known fact that light from the Sun takes about 499 seconds to reach Earth. However, there is such a thing as time dilation; different observers experience time differently due to there ...
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vote
1
answer
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Is distance always 0 relative to an object moving at speed of light $c$? [closed]
As I understand it, when an object is traveling at the speed of light, relative to itself all travel is instantaneous and the distance is zero. If a photon traveling from the sun was aligned with the ...
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2
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Is space-time a property of mass?
Imagine looking at a quasar millions of light years away. From your perspective, a photon emitted by the quasar has spent millions of years travelling through space, and its trajectory has been ...
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1
answer
2k
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Why doesn't light travel instantly? [duplicate]
I've read that the faster you travel in space, the slower you travel in time.
And when you reach the speed of light (which we won't be able to) time will stand still.
So when light travels at the ...
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3
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487
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Why do we say that light travels at a speed? [duplicate]
According to Einstein's theory of relativity, the more speed something has the slower that time passes for it; and presumably when traveling at the speed of light, time stops entirely. So this means ...
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3
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Length contraction speed of light
The Special Theory of Relativity tells us that a moving object eg spaceship measures shorter in its direction of motion as its velocity increases.
At the speed of light it would have zero length, but ...
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2
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Is the non-existence of a rest frame for photon in vacuum a consequence of the second postulate?
So there are multiple reasons given as to why does a photon (or any massless particle) have no rest frame (inertial, of course). I perfectly understand all the possible explanations one can give - it ...
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3
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If time is relative, how could time pass? [duplicate]
EDIT:
I appreciate people who answered below. But it does not answer the question, so I will clarify my questions:
-It seems like everyone is saying that time passing is actualized by physical ...
3
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2
answers
544
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Do photons have absolute motion?
Absolute rest is not possible as the concept of motion is relative. But can we assert that photons have absolute motion as the observers in all the frames of reference would agree to the same value of ...
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1
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Is Lorentz transformation applicable of light itself?
I've just studied Einstein's Special Theory of Relativity and have followed most part of it. I was just wondering that whether the equations of Lorentz transformation are applicable on light? i.e. can ...
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1
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Why is it more acceptable to assume that photons move at the universal speed limit instead of near it?
If both choices explain the same experimental observations, then the latter seems more reasonable. In the former case, the frame of reference of a photon would look like everything in the universe, ...
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2
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Does a graviton in vacuum have a rest frame?
I have read these questions:
Does a photon in vacuum have a rest frame?
Based on dmckee's answer, the answer is no to a photon's rest frame.
In the modern view each particle has one and only one ...
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2
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Does a photon also come to rest after some time while travelling through a medium?
If you fire a bullet in air, after some time it comes to rest because of air resistance forces. But what about photons? If they are also particles, then the same thing should happen with them. It ...
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2
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Can light travel with a speed less than its speed at same time?
I know that the velocity of light with respect to anything is constant ($c$) . What, then, is velocity of light with respect to light?
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