Photon

[Findthepin1]

Photons move at the speed of light so time doesn't pass for them. If time doesn't pass for them they can't be moving from their own perspective. How does that work?

[KerikBalm]

It gets even weirder... relativistic length contraction mean that from a photon's perspective... the universe has no volume.

No time... and no space... things are clear getting arbitrarily close to lightspeed... but actual lightspeed? its like what is on the other side of an even horizon... diving by zero.... I don't quite know either

[Findthepin1]

That's another thing. If the universe has no volume from the photon's perspective, how can it go in any specific direction?

Edited November 6, 2015 by Findthepin1
it's a photon :D

[lajoswinkler]

Maybe from photon's perspective, direction is meaningless. It is formed and is destroyed in the same moment.

[Findthepin1]

Maybe from photon's perspective, direction is meaningless. It is formed and is destroyed in the same moment.

Destroyed? AFAIK photons can't be destroyed. Absolutely crazy amounts of energy can theoretically be turned into matter, but that doesn't actually happen by chance.

[Nikolai]

Destroyed? AFAIK photons can't be destroyed.

They can, and are all the time when they hit matter and are absorbed. Technically, even when a photon is "reflected", what happens is that the initial photon is absorbed and a new photon is re-radiated.

But what other posters have said here is correct. The universe appears to have zero width in its direction of travel in the photon's reference frame, and since it travels at light speed and can go no other speed in a vacuum, it is created and destroyed instantaneously (from its perspective).

[peadar1987]

Even when travelling through a medium, photons still travel at light speed. One photon will jump at light speed from one molecule to the next, then another photon will jump with a slight delay. The beam of light travels slower than the speed of light in a vacuum, but the individual photons still move at c. Just thought that was interesting

[Gaarst]

Has no mass, but is affected by gravity = It's magical. Disregard any sort of 'science' about photons, because I'm pretty sure we have no idea how light actually works, any more than gravity.

This is so wrong; like really, really, really wrong, in all aspects you can possibly imagine.

Has no mass, but is affected by gravity = It's magical.

General Relativity states that gravity distorts space and time, so mass doesn't matter: particles without mass will be affected by gravitation (maybe not all types of particles, but photons are definitely affected by it, it is observed empirically).

Disregard any sort of 'science' about photons, because I'm pretty sure we have no idea how light actually works

We do actually, thanks to Maxwell, Einstein, Planck and ultimately everyone who helped creating the standard model (which even though incomplete is pretty accurate) and quantum mechanics.

any more than gravity

Then again, we pretty much know how this works, thanks to Newton and Einstein (again). Except in black holes or at really high energies (like Big-Bang high); thing is we don't really know how anything works in singularities.

[K^2]

If time doesn't pass for them they can't be moving from their own perspective. How does that work?

You cannot have "perspective of photon". It's not a valid frame of reference precisely for the reasons you've stated. In particle physics, sometimes it's convenient to define light-front coordinates, but it only works because we take something that moves "almost" as fast as a photon as our reference frame. In these coordinates, some quantities become almost negligibly small, while others extremely large. Which allows to simplify computations. But it's precisely the fact that it's not actually light speed, and these quantities aren't exactly zero or actually infinite that allows us to carry out computations to begin with.

[YNM]

Actually, photons goes trough no distance and no time is called null trajectory/geodesic/path. In most metrics that makes time as an "axis" and reassert that they move at it's own speed, or it limits the so-called light cone.

[maltesh]

That's another thing. If the universe has no volume from the photon's perspective, how can it go in any specific direction?

Relativistic length contraction shrinks distances parallel to the direction of motion. As you approach the speed of light, the distance you experience between your source and destination approaches zero, and the time you experience to get from source to destination /also/ approaches zero.

From the nonexistent "photon viewpoint", source and destination are in the same place, so it takes zero time to go from one to the other.

[K^2]

Relativistic length contraction shrinks distances parallel to the direction of motion.

Which is consistent with "universe has no volume" claim. Although, I also found it to be oddly phrased.