# Does a photon experience time or space?

1. Jul 20, 2009

### dshea

2. Jul 20, 2009

### nnnm4

That's kind of an unanswerable question. How can something without complexity (in a certain sense) "experience" anything. A brain is required.

3. Jul 20, 2009

### negitron

Well, in this case "experience" is simply a colloquialism (and a common one in popular science journalism) meaning "affected by". That being the case, it's pretty well agreed by mainstream physicists that photons do not, in fact, "experience" time; that is to say, they do not age.

4. Jul 20, 2009

### dshea

Your answer seems philosophical and if you want to go that way, does a pencil not experience time? How about bacteria, a bug, a fish, a cow,..., or even a human being. I'm sort of interested in the philosophical side of this discussion, however I was wondering based on current scientific theories (insert above question)

5. Jul 20, 2009

### dshea

so can a photon have spin?

6. Jul 20, 2009

### negitron

According to the Standard Model, photons are particles with spin 1. So, yes.

7. Jul 20, 2009

### Math Is Hard

Staff Emeritus
A pencil is affected by time, but does not experience it. Things with sensory systems and brain structures to process incoming sensory data may have the experience of events occurring in sequence and may be able to make use of it. Most humans have a time experience; bacteria, eh.. probably not. For critters in between it gets more interesting and a bit more testable.

8. Jul 20, 2009

### dshea

Thank you so far for your answers, I am loving this forum. As an observer Is the spin part of the photons energy? How much energy is in a photon?

9. Jul 20, 2009

### negitron

Do I really need to link to a definition of colloquialism?

10. Jul 20, 2009

### negitron

No, it's an intrinsic property of all photons.

A photon's energy is given by E = hf, where E is the energy, h (actually h-bar, but I don't know how to type that) is the Planck constant and f is the frequency.

11. Jul 20, 2009

### maverick_starstrider

This question seems a lot more complex to me. Applying Robertson's Equality (essentially Heisenberg's uncertainty) $\Delta E \Delta t \geq \frac{\hbar}{2}$ which implies a potential energy fluctuation in time.

12. Jul 20, 2009

### dshea

If a photon leaves it's source and it is not affected by time and space at which point I absorb the photon, does it therefore imply that the source had interacted with me. To further develop my question so that you understand what I am thinking. The source is in a way passing it's energy directly to me. In a way I am interacting with something that existed possibly millions of years ago.

13. Jul 21, 2009

### maverick_starstrider

I wish I could provide you with an intuitive easy answer but unfortunately quantum doesn't work that way. I'd imagine you're more or less visualizing a photon being ejected from a scattering event like someone flicking a pee with their finger or some such. However, the photon is a spin 1 boson with a quantum wavefunction propogating through space. Depending on what you're trying to do to the photon or how you're trying to measure it the convenience of a "timeless particle" perspective vs. "a continuously fluctuating entity popping in and out of existance along a signal trajectory" perspective is impossible to distinguish. It propogates like a spin 1 boson. The application of terms like "timelessness" and "experience" is really dubious. In other words we can exactly model its behaviour but conveying that to such vague english terms is always going to be problematic. ESPECIALLY a question like "how OLD is it"

14. Jul 21, 2009

### apeiron

Google cramer and transactional interpretation of QM if you want some sort of thinking along these lines.

15. Jul 21, 2009

### sas3

As I understand it since a photon has no rest mass it must travel at the speed of light and anything traveling at the speed of light does not move through time (i.e. time stops). So for a photon space/time does not exist.
From a photons point of view it never gets to go anywhere, or does it get to go anywhere in no time, Is it a partial is it a wave, or both at the same time, Dam that’s right time doesn’t exist.
OUCH !

16. Jul 21, 2009

### dshea

maverick I wish you could provide me with an intuitive easy answer. On the other hand I have avoided understanding things based on their difficulty for far to long and am pulling up my sleeves and going to work. Gotta start somewhere right! Now what do you mean a spin 1 boson (I know what it means to propagate). Also because of the law of contraction, if light is a particle would it be two dimensional (our perspective). Is it possible for us to view/measure a single photon?

P.S. I will be asking a lot of questions as I have so many of them.

17. Jul 21, 2009

### ibcnunabit

If you interpret the question as whether the change of position or time elapses from the photon's perspective, no, it doesn't. This has interesting consequences, and I believe is one of the prime reasons for many of the peculiarities of light as seen from our perspective in which distance and time DO elapse in our observations of light. (Double slit experiment, etc.)

18. Jul 21, 2009

### maverick_starstrider

The double slit experiment is the result of wave-particle duality. You can perform the double slit experiment with electrons onto phosphorous paper and get the same result. There's nothing special about light.

19. Jul 21, 2009

### maverick_starstrider

A boson is a particle which:
-has an integer spin
-the spatial component of the total wavefunction of a two/multi boson system is symmetric
-they do no follow the pauli exclusion principle (which applied to fermions)
These 3 things are actually all the exact same property stated in different ways. All the messenger particles are bosons (photons, gauge boson's, etc.) as is, for example a helium atom.

I do not understand what you mean about light being 2-dimensional. All particles, including photons, have a quantum wavefunction which is essentially a probability amplitude which inherently obeys Heisenberg's Uncertainty principle (which is actually a specific case of Robertson's Inequality). Therefore, the notion of the EXTENT of a particle is inherently fuzzy just as much as its position is.

And yes, you can detect an individual (real) photon. This was the essence of the double slit experiment. The fact that one observes an interference pattern even though only a single photon is going through the apparatus at a given time http://en.wikipedia.org/wiki/Double_slit_experiment

20. Jul 21, 2009

### dshea

I must say maverick your answers are clear, and you have been very helpful to my understanding thus far. As for light being 2-dimensional I may have been jumping to a conclusion that may have been false. My conclusion came from an observers point of view. If there was a spaceship that was traveling from left to right, as it approached the speed of light I would notice its contraction the closer it came to c. My conclusion was that since light traveled at c that as an observer it would have contracted into a 2 dimensional something. I think of black holes in the same way, all the particles are traveling all directions towards the center at increasing speed reaching c giving a black hole its singularity structure from the point of an observer. If I'm way off track can you set me right?