# Does a photon experience time or space?

#### dshea

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#### nnnm4

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

#### 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.

#### 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)

#### dshea

so can a photon have spin?

#### negitron

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

#### Math Is Hard

Staff Emeritus
Gold Member
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.

#### 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?

#### negitron

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

#### negitron

As an observer Is the spin part of the photons energy?
No, it's an intrinsic property of all photons.

How much energy is in a photon?
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.

#### 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.

#### 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.

#### 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"

#### apeiron

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

#### sas3

Gold Member
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 !

#### 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.

#### 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.)

#### maverick_starstrider

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.)
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.

#### maverick_starstrider

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.
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

#### 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?

#### maverick_starstrider

Well a spaceship going near the speed of light will appear to contract (lorentz contraction) in the direction of its motion (your vantage point is irrelevant). So, for example, if you were to be directly behind said spaceship you would not notice any contraction at all since it's only contracting length wise (not width wise). i.e. if you're watching the U.S.S. enterprise do its silly warp speed animation and you're looking at it from the side it's going to contract, however, if you're staring at its butt from directly behind it you wouldn't notice anything since that's not the axis through which it is approaching a speed near c relative to you.

A black hole is also in no way 2-dimensional, spatially it is 3-dimensional in extent. It's not like a vinyl record that you could look at on edge it is a sphere.

#### maverick_starstrider

I imagine the confusion over the shape of a black hole (assuming I understand your visualization correctly) is because of images like this: http://lgo.mit.edu/blog/drewhill/files/blackhole.gif [Broken] however, general relativity exists in 4 dimensions, 3 spatial (x,y,z) and time however one cannot draw a picture of time however that is what these illustrations are trying to do. As you see the 2d grid fold it's not folding relative to the 3rd spatial dimension but in the temporal dimension. In other words the z-axis in these pictures is not in meters, it's in seconds. It's an attempt to visualize a 4-dimensional object in 3-dimensions.

Or maybe you're visualizing this http://thesamerowdycrowd.files.wordpress.com/2008/12/black-hole.jpg which is showing an accretion disk around the black hole (the hole itself is not flat like the plane of the accretion disk). For an explanation of why accumulated dust and such in space tend to form these 2d planar disks I'll simply refer you to wikipedia http://en.wikipedia.org/wiki/Accretion_disk

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#### DaveC426913

Gold Member
Also because of the law of contraction, if light is a particle would it be two dimensional (our perspective).
Modeled as a particle, a photon is a point, i.e. zero dimensions.
Is it possible for us to view/measure a single photon?
Yes, using a photon detector.

#### dshea

Well a spaceship going near the speed of light will appear to contract (lorentz contraction) in the direction of its motion (your vantage point is irrelevant). So, for example, if you were to be directly behind said spaceship you would not notice any contraction at all since it's only contracting length wise (not width wise). i.e. if you're watching the U.S.S. enterprise do its silly warp speed animation and you're looking at it from the side it's going to contract, however, if you're staring at its butt from directly behind it you wouldn't notice anything since that's not the axis through which it is approaching a speed near c relative to you.

A black hole is also in no way 2-dimensional, spatially it is 3-dimensional in extent. It's not like a vinyl record that you could look at on edge it is a sphere.
I understand all of this. When I think of looking at a black hole I think of the first visualization you listed below, however I am not thinking of it as a record player, more as a whirlpool that if you moved the center of the whirlpool would seem to move with you. Thats if the blackhole is not spinning or anything.

I imagine the confusion over the shape of a black hole (assuming I understand your visualization correctly) is because of images like this: http://lgo.mit.edu/blog/drewhill/files/blackhole.gif [Broken] however, general relativity exists in 4 dimensions, 3 spatial (x,y,z) and time however one cannot draw a picture of time however that is what these illustrations are trying to do. As you see the 2d grid fold it's not folding relative to the 3rd spatial dimension but in the temporal dimension. In other words the z-axis in these pictures is not in meters, it's in seconds. It's an attempt to visualize a 4-dimensional object in 3-dimensions.

Or maybe you're visualizing this http://thesamerowdycrowd.files.wordpress.com/2008/12/black-hole.jpg which is showing an accretion disk around the black hole (the hole itself is not flat like the plane of the accretion disk). For an explanation of why accumulated dust and such in space tend to form these 2d planar disks I'll simply refer you to wikipedia http://en.wikipedia.org/wiki/Accretion_disk
Thanks for the source on the accertion disk though this wasn't really what I was imagining.

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#### maverick_starstrider

Ya, the point is, a black hole is 3-dimensional sphere of space from which light cannot escape. It's TIME (or rather the time dimension) that's spiking downward like that.

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