<p>Time does not exist for photons.  Quoting <a href="https://en.wikipedia.org/wiki/Proper_time" rel="nofollow noreferrer">Wikipedia</a>'s somewhat unnecessarily technical page:</p>

<blockquote>
  <p>In relativity, proper time along a timelike world line is defined as the time as measured by a clock following that line.</p>
</blockquote>

<p>The proper time between any two points along any photon's path in empty space is zero.  So the photon "experiences" no passage of time.</p>

<p>It's not very clear to me how this could explain the double-slit experiment. Proper Time is an entirely relativistic concept, whereas the double slit results are <em>not</em> explained by relativity, but are explained by Quantum Mechanics.</p>

CC BY-SA 4.0
2018-08-03T14:28:29.980Z
Why not stick with the wave-like method of explaining Double-Slit?  Or are you referring to the more recent experiments showing a single photon going thru both, or even different quantum numbers going thru different slits?
Carl Witthoft
CC BY-SA 4.0
2018-08-03T17:03:24.693Z
[The people who wrote that Wikipedia article specifically tried to prevent it from being read in the way that you are reading it](https://en.wikipedia.org/w/index.php?title=Talk:Proper_time&oldid=694143511#Proper_Time_for_Lightlike_Interval).
JdeBP
CC BY-SA 4.0
2018-08-04T14:35:19.667Z
Mark, the photon doesn't take zero time to traverse from point A to point B. During that traversal I can put an asteroid in its way. It's the same for you  if you're travelling at 99.99999999999% of the speed of light. You won't be aware of me putting that asteroid in your way. But BLAM! and everybody else will. Then everybody else will concur that time _did_ exist for you, even if you weren't aware of it.
John Duffield
CC BY-SA 4.0
2018-08-04T14:57:22.800Z
@John Duffield: I didn't say that the photon takes zero time to traverse its path.  I said the *proper time* along the path is zero, which is quite a different thing.  Proper time essentially is the time a clock moving along a path in spacetime records as elapsed. It is **not** what an outside observer experiences, which is what you're speaking of.  You can see that the zero time experienced by a photon is the limit of the time experienced by a spaceship as the ship approaches lightspeed. The faster the ship goes, the less time is experienced onboard, asymptoting to zero at lightspeed.
Mark Olson
CC BY-SA 4.0
2018-08-04T15:10:35.523Z
You also said _time does not exist for photons_, but it does. Ditto for those people on the ship. They might experience no time, but it still takes them 4 years to get to Alpha Centauri. That's if I don't put an asteroid in _their_ way. Time exists for them even though they don't experience any. So that's a -1 from me I'm afraid.
John Duffield
CC BY-SA 4.0
2018-08-04T16:00:33.143Z
OK. Last time. Of course people on the ship experience time. *Everything* travelling slower than light experiences time. But the amount of time experienced (proper time) any any particular path decreases as you approach the speed of light. And *at* lightspeed no proper time elapses at all.  If you wish to keep going, please take it to chat.
Mark Olson
CC BY-SA 4.0
2018-08-03T13:58:32.170Z
2018-08-03T13:58:32.170Z
Mark Olson
<p>If time slows down the closer you get to the speed of light, does it follow that time does not exist for photons. Do photons - even if they travel across billions of light years of space - arrive at the same time as they are created?
And if this is so, does this not explain the peculiarities of the double-slit experiment?</p>

CC BY-SA 4.0
2018-08-03T14:29:01.213Z
Please identify exactly which double-slit phenomenon you're referring to.
Carl Witthoft
CC BY-SA 4.0
2018-08-03T14:32:13.320Z
Electrons also show interference pattens passing through a double slit, and they do not travel at c.
James K
CC BY-SA 4.0
2018-08-03T14:33:01.767Z
I'm voting to close this question as off-topic because this a pure physics question with no astronomy
James K
CC BY-SA 4.0
2018-08-03T15:12:56.567Z
A pure physics question and I'd suggest you start reading at [Would Time Freeze if you could travel at the speed of light ?](https://physics.stackexchange.com/questions/29082/would-time-freeze-if-you-could-travel-at-the-speed-of-light?noredirect=1&lq=1) on Physics SE.
StephenG - Help Ukraine
CC BY-SA 4.0
2018-08-03T18:08:58.157Z
This is on the hot network. Shame it needs to be closed.
Sir Cumference
<light><space-time><photons><time>
Does Time Exist for Photons?
Dean Chalk
# Does Time Exist for Photons?

(Asked by: username_0 on 2018-08-03)

If time slows down the closer you get to the speed of light, does it follow that time does not exist for photons. Do photons - even if they travel across billions of light years of space - arrive at the same time as they are created?
And if this is so, does this not explain the peculiarities of the double-slit experiment?

**Tags:** light, space-time, photons, time
> **Comments:**
> **username_1**: Please identify exactly which double-slit phenomenon you're referring to.  
> **username_2**: Electrons also show interference pattens passing through a double slit, and they do not travel at c.  
> **username_2**: I'm voting to close this question as off-topic because this a pure physics question with no astronomy  
> **username_3**: A pure physics question and I'd suggest you start reading at [Would Time Freeze if you could travel at the speed of light ?](https://physics.stackexchange.com/questions/29082/would-time-freeze-if-you-could-travel-at-the-speed-of-light?noredirect=1&lq=1) on Physics SE.  
> **username_4**: This is on the hot network. Shame it needs to be closed.  

---

## 1 answers

### Answer by username_5 on 2018-08-03. Score: 4

Time does not exist for photons. Quoting [Wikipedia](https://en.wikipedia.org/wiki/Proper_time)'s somewhat unnecessarily technical page:

> In relativity, proper time along a timelike world line is defined as the time as measured by a clock following that line.

The proper time between any two points along any photon's path in empty space is zero. So the photon "experiences" no passage of time.

It's not very clear to me how this could explain the double-slit experiment. Proper Time is an entirely relativistic concept, whereas the double slit results are *not* explained by relativity, but are explained by Quantum Mechanics.

> **Comments:**
> **username_1**: Why not stick with the wave-like method of explaining Double-Slit?  Or are you referring to the more recent experiments showing a single photon going thru both, or even different quantum numbers going thru different slits?  
> **username_6**: [The people who wrote that Wikipedia article specifically tried to prevent it from being read in the way that you are reading it](https://en.wikipedia.org/w/index.php?title=Talk:Proper_time&oldid=694143511#Proper_Time_for_Lightlike_Interval).  
> **username_7**: Mark, the photon doesn't take zero time to traverse from point A to point B. During that traversal I can put an asteroid in its way. It's the same for you  if you're travelling at 99.99999999999% of the speed of light. You won't be aware of me putting that asteroid in your way. But BLAM! and everybody else will. Then everybody else will concur that time _did_ exist for you, even if you weren't aware of it.  
> **username_5**: @John Duffield: I didn't say that the photon takes zero time to traverse its path.  I said the *proper time* along the path is zero, which is quite a different thing.  Proper time essentially is the time a clock moving along a path in spacetime records as elapsed. It is **not** what an outside observer experiences, which is what you're speaking of.  You can see that the zero time experienced by a photon is the limit of the time experienced by a spaceship as the ship approaches lightspeed. The faster the ship goes, the less time is experienced onboard, asymptoting to zero at lightspeed.  
> **username_7**: You also said _time does not exist for photons_, but it does. Ditto for those people on the ship. They might experience no time, but it still takes them 4 years to get to Alpha Centauri. That's if I don't put an asteroid in _their_ way. Time exists for them even though they don't experience any. So that's a -1 from me I'm afraid.  
> **username_5**: OK. Last time. Of course people on the ship experience time. *Everything* travelling slower than light experiences time. But the amount of time experienced (proper time) any any particular path decreases as you approach the speed of light. And *at* lightspeed no proper time elapses at all.  If you wish to keep going, please take it to chat.  

---

