# Photon & Time: Is Movement Possible?

• taylrl3
In summary, the conversation discusses the concept of time and its relationship to photons and other elementary particles. It is argued that photons do not experience the passage of time due to their lack of internal structure, and the concept of "experiencing" something is defined in the context of special and general relativity. It is also suggested that photons form images of the past within our eyes and do not age, and the question is raised about whether electrons experience the passage of time.
taylrl3
I'm just wondering how a photon can move if it does not experience the passage of time?

What makes you think it shouldn't?

How can anything change if does not pass?

Ok, suppose we freeze you cryogenically and put you on a train. When the train moves, do you move?

Ridiculous example. But that shows what I'm trying to express here, which is that the question you asked is not a useful one. You've tried to project human assumptions onto a system which does not know or care about your opinion or how you think things 'ought' to behave. The real way to understand physics is to examine the mathematical formalism, which will then show you that questions as vague as this have no meaning.

Nice response. Thanks :-).

I've just been thinking about it a bit further. In the reference frame of the photon t=0 and always will. Therefore it is not the photon which moves but my movement through time which causes it to reach my eye.
Quite a nice way of seeing how space and time are so intrinsically connected, ay?

Sorry my first response should have said; "how can anything change if TIME does not pass?".
(I should read my messages before posting. lol)

I think the answer might be that there is no 'reference frame of the photon'. If you could have such a frame wouldn't it contract space in the direction of propagation to a point, so that spacetime becomes only three-dimensional in that frame (ie loses a dimension)?

this thread gave me an interesting thought, which is related to the topic.

when we observe photons are we observing them with no time?

so to try to make that clearer, the closer something gets to c the slower time for that thing appears to an observer in a rest frame, so wouldn't a photon appear to be frozen in time to us?

powerplayer said:
when we observe photons are we observing them with no time?
...
wouldn't a photon appear to be frozen in time to us?

We cannot observe photons until they hit something and are detected. Detecting a photon ends its existence. Observing a photon ends its existence. Photons have no appearance while they are in transit, only when they hit something and are detected. We can measure the time at which they hit something and are detected but otherwise, there is no point in trying to determine anything related to time with regard to photons while they are traveling at the speed of light.

I'm just wondering how a photon can move if it does not experience the passage of time?

I like thinking of photons both ways, with the matter wave standing still and the photon expanding at c into it, or the photon standing still with the matter wave dilating into it at c.

"how can anything change if TIME does not pass?".

Time is local and changes are how we count it.

In the reference frame of the photon t=0 and always will. Therefore it is not the photon which moves but my movement through time which causes it to reach my eye.

The photon moves through space at c, we on the other hand must be moving in time at the same speed just to receive these photons with no gaps.

so to try to make that clearer, the closer something gets to c the slower time for that thing appears to an observer in a rest frame, so wouldn't a photon appear to be frozen in time to us?

Does a photon form an image of the past within my eye? I think of these images as my present but in some cases I see an image over a billion light years old.

And does the electron experience the passage of time?

Fredrik said:
For something to actually age, it needs to have an internal structure that can change with time. No elementary particles do, so they can't really age.

For something to really experience the passage of time (or anything else), it needs to be conscious. Things without internal structure certainly can't be conscious.

What we mean when we say that an object or a particle "experiences X" is that in the coordinate system that the standard synchronization procedure associates with the object's world line (or its tangent), some sequence of events is described as "X". That's how the term "experiences" is defined in the context of special and general relativity. The problem is that the standard synchronization procedure doesn't work for null geodesics, i.e. for the curves that can be world lines of massless particles. So the term "experiences" is undefined for photons.

## 1. Can a photon move through time?

According to Einstein's theory of relativity, time is relative and can be affected by speed and gravity. Therefore, it is possible for a photon to move through time, but not in the same way that we perceive time. A photon moves at the speed of light and experiences time at a different rate than we do. From the perspective of a photon, time does not pass at all.

## 2. How does a photon's speed affect its perception of time?

As mentioned before, a photon moves at the speed of light, which is the fastest speed possible in the universe. This means that time for a photon essentially stands still. From our perspective, a photon may travel across the entire universe in a matter of seconds, but for the photon, no time has passed.

## 3. Can photons travel back in time?

While photons can move through time at a different rate than we do, they cannot travel back in time. The concept of time travel is still theoretical and has not been proven to be possible, even for particles like photons that move at high speeds.

## 4. How does light travel through space if time stands still for photons?

Although time stands still for photons, they can still travel through space at the speed of light. This is because space and time are interconnected, and the speed of light is a constant in the universe. So even though time does not pass for a photon, it can still travel through space.

## 5. Is movement possible for anything other than photons?

Yes, movement is possible for all particles and objects in the universe. However, the speed at which they move can affect their perception of time. The closer an object gets to the speed of light, the slower time moves for that object. This is known as time dilation and is a key concept in Einstein's theory of relativity.

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