Do Photons Experience Time?

[Voyager55]

From my current and limited understanding, as you approach the speed of light your time relative to others slows until you reach the speed of light and time entirely ceases to pass. Does this mean the a photon traveling hundreds of millions of light years across the cosmos bounces off multiple objects and ends up in my eye has experienced absolutely no time? Does this mean that from a photon's "perspective" it's essentially just a stretched beam of infinite photons that exists every where that it ever is going to exist at every point in time with which it's ever going to exist?

[miracmert]

Well, I don't know much about this and it bugged me too and I read two different opinions about this and I'm not a physicist so what I'm going to say is probably not more than two opinions:

One thing I read was that even though you could travel at light-speed (imagine looking from a photon's perspective) there is still lightspeed that you are not going to be able to reach because the speed of light is there in every frame, so relative to you there is still light faster than you, going at lightspeed.

Another opinion that I read was that since photons were going at the speed of light which means there is no more time, all of the photons were actually only one photon that is independent of time and can be in any place in the space at the same time (because it's not bounded/limited by time and 3 dimensions anymore).

So yeah these are the different perspectives on the subject that I read looong time ago and I'm not even sure if I remember them correctly, having an explanation from a more-knowing-person here would be better because I'm curious too.

[Bill Phil]

They wouldn't experience time like us, if they do. Maybe time is a position relative to a photon?

[maltesh]

From my current and limited understanding, as you approach the speed of light your time relative to others slows until you reach the speed of light and time entirely ceases to pass. Does this mean the a photon traveling hundreds of millions of light years across the cosmos bounces off multiple objects and ends up in my eye has experienced absolutely no time? Does this mean that from a photon's "perspective" it's essentially just a stretched beam of infinite photons that exists every where that it ever is going to exist at every point in time with which it's ever going to exist?

Yes, the photon has experienced no time.

From the viepoint of the photon, (inasmuch as can be said that the a photon can have a viepoint), the universe has zero thickness in the direction of its motion, thanks to relativistic length contraction. So to the photon, its source and destination are in the same place.

That said, the photon doesn't /actually/ bounce off things. It goes from its source, hits an atom, and the atom absorbs its energy. Then, after some finite amount of time, the excited atom emits a photon of the same energy as the one that struck it..

[Tommygun]

Yes, the photon has experienced no time.

From the viepoint of the photon, (inasmuch as can be said that the a photon can have a viepoint), the universe has zero thickness in the direction of its motion, thanks to relativistic length contraction. So to the photon, its source and destination are in the same place.

That said, the photon doesn't /actually/ bounce off things. It goes from its source, hits an atom, and the atom absorbs its energy. Then, after some finite amount of time, the excited atom emits a photon of the same energy as the one that struck it..

This made me think of a photon from the Big Bang existing in the past, present and future all in the same instant.

[LordFerret]

From everything I've read and understand thus far: Photons are generated deep within a star's core (gamma rays and neutrinos), and travel to the surface via convection currents (absorbed and re-emitted by atoms enroute) before being emitted from the photosphere. The current belief of transit time in those convection currents is anywhere from 1 to 3 million years ... meaning those photons are not traveling at 'light speed'. That tells me they're 'experiencing' time.

[Camacha]

That said, the photon doesn't /actually/ bounce off things. It goes from its source, hits an atom, and the atom absorbs its energy. Then, after some finite amount of time, the excited atom emits a photon of the same energy as the one that struck it..

Is this actually accurate?

[xXIndestructibleEVAXx]

Is this actually accurate?

Yes. It's part of quantum mechanics.

[-Velocity-]

From everything I've read and understand thus far: Photons are generated deep within a star's core (gamma rays and neutrinos), and travel to the surface via convection currents (absorbed and re-emitted by atoms enroute) before being emitted from the photosphere. The current belief of transit time in those convection currents is anywhere from 1 to 3 million years ... meaning those photons are not traveling at 'light speed'. That tells me they're 'experiencing' time.

You're taking a oft-stated fact about how long it takes energy from the core of the Sun to reach the surface far too literally. Photons produced in the core of the Sun never make it to the surface. Any source that says so is wrong. ENERGY produced in the core of the Sun takes millions of years to reach the surface. If the photons produced in the core of the Sun actually reached the surface, then the Sun would have the spectrum of a 16 million degree Celsius blackbody. We'd be bombarded by vast amounts of gamma rays and x-rays, and life on Earth could not exist. In fact, the Sun has a spectrum of a 6000 degree C blackbody, and its radiant power peaks in visible light, not x-rays or gamma rays. That's because all the photons we receive from the Sun originate on the surface, where it's relatively cool.

What actually happens in the Sun is that photons produced in the core (a lot of gamma rays) get absorbed by solar material, heating that material. The solar material then emits new photon(s) at a different wavelength, a wavelength dependent on the solar material's temperature, according to Planck's Law.

And also, just because the effective speed of light is slower through a medium (like glass) doesn't mean the photons are actually moving slower. The photons move at light speed between their interactions with atoms, and those interactions don't slow them down, they just absorb/re-emit them. Though really, it's overly complicated to use the particle behavior of light to understand how light propagates through refractive mediums, it's much better to look at it as a wave.

[YNM]

From everything I've read and understand thus far: Photons are generated deep within a star's core (gamma rays and neutrinos), and travel to the surface via convection currents (absorbed and re-emitted by atoms enroute) before being emitted from the photosphere. The current belief of transit time in those convection currents is anywhere from 1 to 3 million years ... meaning those photons are not traveling at 'light speed'. That tells me they're 'experiencing' time.

The 1 - 3 billion years is measured by our clocks, not photon clocks - not to mention they're different photon. Look up mean free path.

Or, else, think this way: In a huge, flat endless grassfield, and in a traffic jam, where will your car are likely going faster ? In a traffic jam, your car stops every now and then because of the car in front of you started to go away, then stops again because the car at your front stops (even probably reversing some other time). On the field, you can roam anywhere as you like, as straight as you like, as fast as you like.

The same happen to photons - Sun is an extremely dense thing for them that they only goes a short way after being emitted from one particular event / matter before absorbed again by another matter. But once it's not so dense, they can just go away as fast and as unobstructed as they like - this tendency is called optical depth. Neutrinos, on the other hand, while most likely having mass, they don't interact easily with Sun's matter - they just merely passing it at near-lightspeed.

Even you can search for attempts where people have "stopped" light to slower than walking speed by using cryogenics.

[impwarhamer]

Micheal talked about this recently on vsauce

[LordFerret]

You're taking a oft-stated fact about how long it takes energy from the core of the Sun to reach the surface far too literally. Photons produced in the core of the Sun never make it to the surface. Any source that says so is wrong. ENERGY produced in the core of the Sun takes millions of years to reach the surface. If the photons produced in the core of the Sun actually reached the surface, then the Sun would have the spectrum of a 16 million degree Celsius blackbody. We'd be bombarded by vast amounts of gamma rays and x-rays, and life on Earth could not exist. In fact, the Sun has a spectrum of a 6000 degree C blackbody, and its radiant power peaks in visible light, not x-rays or gamma rays. That's because all the photons we receive from the Sun originate on the surface, where it's relatively cool.

What actually happens in the Sun is that photons produced in the core (a lot of gamma rays) get absorbed by solar material, heating that material. The solar material then emits new photon(s) at a different wavelength, a wavelength dependent on the solar material's temperature, according to Planck's Law.

And also, just because the effective speed of light is slower through a medium (like glass) doesn't mean the photons are actually moving slower. The photons move at light speed between their interactions with atoms, and those interactions don't slow them down, they just absorb/re-emit them. Though really, it's overly complicated to use the particle behavior of light to understand how light propagates through refractive mediums, it's much better to look at it as a wave.

Did I not state: "(absorbed and re-emitted by atoms enroute)" ???

[ZetaX]

Did I not state: "(absorbed and re-emitted by atoms enroute)" ???

Yes, but you seemed to think that this makes the photons very slow, while in reality there is no photon most of the time, or it is "bouncing" around.

[LordFerret]

The 1 - 3 billion years is measured by our clocks, not photon clocks - not to mention they're different photon. Look up mean free path.

Or, else, think this way: In a huge, flat endless grassfield, and in a traffic jam, where will your car are likely going faster ? In a traffic jam, your car stops every now and then because of the car in front of you started to go away, then stops again because the car at your front stops (even probably reversing some other time). On the field, you can roam anywhere as you like, as straight as you like, as fast as you like.

The same happen to photons - Sun is an extremely dense thing for them that they only goes a short way after being emitted from one particular event / matter before absorbed again by another matter. But once it's not so dense, they can just go away as fast and as unobstructed as they like - this tendency is called optical depth. Neutrinos, on the other hand, while most likely having mass, they don't interact easily with Sun's matter - they just merely passing it at near-lightspeed.

Even you can search for attempts where people have "stopped" light to slower than walking speed by using cryogenics.

Old news. I remember the day the announcement was released... the implications tied to hopes for data transmission.

http://adsabs.harvard.edu/full/1992ApJ...401..759M

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Yes, but you seemed to think that this makes the photons very slow, while in reality there is no photon most of the time, or it is "bouncing" around.

Not very slow, but not at 'light speed' either... as demonstrated in the Monte Carlo study. And they are, in essence doing exactly that - bouncing around. (Edit: Yes, I know, apples and oranges, but it does apply.)

Edited March 5, 2015 by LordFerret

[ZetaX]

Not very slow, but not at 'light speed' either... as demonstrated in the Monte Carlo study. And they are, in essence doing exactly that - bouncing around. (Edit: Yes, I know, apples and oranges, but it does apply.)

What "Monte Carlo study" are you talking about?

And them bouncing around (by the way a huge oversimplification) is a huge difference. Would you actually claim that a car on a racetrack driving in circles has speed 0 because it always comes back to where it started?

[LordFerret]

What "Monte Carlo study" are you talking about?

And them bouncing around (by the way a huge oversimplification) is a huge difference. Would you actually claim that a car on a racetrack driving in circles has speed 0 because it always comes back to where it started?

The Monty Carlo reference was with regard to a somewhat different study - photon migration through tissue ... but it does apply. The actual reference I had in mind (but referred to improperly) was...

http://physics.wooster.edu/JrIS/Files/Walker_Web_Article.pdf

That's the bouncing around I'm referring to. I don't think your car and racetrack analogy fits here.

[Camacha]

So, when we are talking about bouncing, you actually mean it being absorbed and re-emitted, right? This seems quite a difference.

What is not clear to me is how a photon reflects off a surface, as in, makes things shiney. How come the angle of the newly formed photon following a mirror trajectory/bouncing off at the same but opposite angle it arrived?

[-Velocity-]

What is not clear to me is how a photon reflects off a surface, as in, makes things shiney. How come the angle of the newly formed photon following a mirror trajectory/bouncing off at the same but opposite angle it arrived?

Viewing light as a solely particle phenomenon, you're going to run into things that don’t make sense. Like everything else, electromagnetic radiation is a wave phenomenon, and you can’t understand how it works without acknowledging this.

Let’s look at a partial example of how light reflects off of a perfect electric conductor (PEC). The electric field must go to zero in a perfect electric conductor. Metals are very close to being PECs, which is why they are “shiny†when polished smooth as compared to the wavelength of light. A PEC can support a surface charge, so they can have electric fields that are normal to their surface, but any tangential electric fields are neutralized by the flow of charge. Furthermore, the accumulation of surface charges screens any normal electric fields and prevents them from penetrating into the PEC.

For simplicity, I’ll only show you half of a solution- I’ll only look at electric fields and one polarization case, but it will hopefully get the point across. Imagine an incident electromagnetic wave coming in from a random angle. In this example, the polarization is such that the electric field is tangential to the surface of the PEC. When that electromagnetic wave reaches the surface of the PEC, the boundary condition of the PEC- that tangential electric fields go to zero- forces the surface to "launch" a reflected wave that exactly cancels out the electric field right at the surface boundary. There are boundary conditions that apply for magnetic fields too, and that relate them to surface currents, and these are equally important, but I’m trying to keep things simple here, so I’m only presenting half of the solution. Suffice it to say, the boundary conditions set that the direction of the reflected wave follows the law of reflection (the angle is the same but opposite). But hopefully, this example should get the point across that you really can’t ignore the wave nature of light.

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Did I not state: "(absorbed and re-emitted by atoms enroute)" ???

But it's not true that the same photons were absorbed and re-emitted in route. The photons are absorbed and their identities- as much as they can be said to have identities- is gone. The photons that are re-emitted are of a different wavelength, and contain different quantum information. They are entirely different particles. Imagine that you shine an invisible ultraviolet laser beam (just as an example, but any light source of any wavelength would do for this example) on a piece of metal and heat that metal until it's glowing red-hot, then turn the laser off and record the photons emitted by the heated metal. The metal continues to glow even though the laser is off, because energy is stored in vibrations of the particles that make the metal up. The photons emitted by the red hot metal are NOT coherent ultraviolet laser light. They are entirely different photons, and emitted at a spread of wavelengths determined by the temperature of the metal and Planck's law for thermal blackbody radiation. THAT is what is going on inside the Sun. It is entirely false to claim that photons in the center of the Sun can ever make it to the surface. It is only the energy produced in the center of the Sun makes it the surface.

Edited March 5, 2015 by |Velocity|

[YNM]

Quite important to get some better view on the absorption - reemittance : p-p chain in Sun (that gives Sun it's enourmous luminosity) produces gamma rays, yet the radiation from the surface of Sun peaks up in yellow - green portion of visible wavelength. The photons you see from Sun's surface aren't the same with those directly from the p-p chain - different photons, just enough amount to ensure hydrostatic equilibrium (by emitting the same amount of energy, so radiation pressure doesn't build up inside) and also, temperature gradient as one of the implication.

Edited March 8, 2015 by YNM