something about physics, light in space

Lets say I got a photon, travelling at light speed, in a completley empty region of space. No stars, no plants, nothing.
From Einstein theory, light always travel at the speed of light, no matter who measures it, but in an empty region of space, it’s impossible to measure this speed because the speed of an object is something which is relative to other objects.

How will this photon behave? what will it look like?

My English is not so good so I hope I made myself clear


Well if it behaves and looks like there must be someone measuring it, so it’s just a regular photon, nothing special.

We don’t know without looking. Once we look, it is no longer alone. What’s it doing while we’re not looking? We have absolutely no idea other than what is probable, but anything’s possible.

See above.

Anyway, no matter if it is in space or not, as long as it is within the known universe it is travelling relative to something else. It does not exists in a totally unrelated vacuum of nothingness.

And for that matter we know its speed without needing anything to refer it to. In fact, if you measure its speed using two different objects as your references, and the two objects are moving at speeds different from each other, both your speeds for the photon will be equal. It was trying not to make any assumptions that violated this condition that lead Einstein to question the role of time and space and come up with the special theory of relativity.

Thanks for the answers

Lets say some superbeing is looking at it, not interrupting its movement.
So you look at the photon moving, but moving relative to what?
It can look like it is standing still, but it’s impossible for a photon to do.
According to Einstein special relativity, you get different views from different ovservers. If two people are in an empty region of space, and of them is moving, you can’t tell which one it is and each one will say the other is the one that is moving.

Another question:
If I put two photons in an empty region of space, does the photon have a point of view?
It can not be in rest, because it doesn’t exist if it’s not moving.
Will we be able to determine if both of the photons are moving?
What will each photon “say” about the other?

Thanks again

Any observers, regardless of their speeds with respect to one another, will all measure the photon as moving at the speed of light. Two people moving in opposite directions near the speed of light will both measure the photon’s speed as the speed of light.

Can’t remember what happens if someone riding on a photon at the speed of light measures the speed of another photon moving right alongside. Funny things happen at c. You would think he would measure the other photon’s speed as zero but not sure that’s the case. If you’re moving at the speed of light, your time dilation is infinite. Haven’t seen the equations for all this stuff in many years, though.

My understanding exactly. The speed of light is what you use as a base for any movement.
But what happens if (Hypothetically) only one atom exists in our universe! Does one measure it compartive to the speed of light? Who’s around to measure it?
Is there a “Speed of Light?” if no cognizant being is in existence?

My understanding exactly. The speed of light is what you use as a base for any movement.
But what happens if (Hypothetically) only one atom exists in our universe! Does one measure it compartive to the speed of light? Who’s around to measure it?
Is there a “Speed of Light?” if no cognizant being is in existence?

A photon can’t have a frame of reference because light must move at c relative to all frames of reference and light can’t move at c with respect to light.

So any questions wrt to what a photon would see or what time it would experience are meaningless.

That being said Albert proposed a thought experiment called “Riding on a Light Beam.” He realized that were this possible he would see a non time varying spatial waveform and since light is composed of time varying electric and magnetic fields it couldn’t exist.

This is what made him realize that nothing with mass can travel at c. (Or so they say)

Hmm, with a little work, we might be able to work this argument into a disproof of God. “If God made a universe with only one photon, would it be moving at c?” or something like that.

Something rude, no doubt.

To expand upon that; a photon does not experience movement in the “time” direction; as far as it is concerned (assuming some kind of metaphorical awareness) it would exist as a waveform extending from genesis to terminus, continuous and unchanging throughout spacetime. Similarly, it would see other photons, and indeed, all particles, as being strings rather than discrete entitites. In a sense, all particles are moving at c, but some have a significant portion of that “velocity” in the time direction, while the massless photon onlhy measures motion through the spacial dimensions.

So, photons can’t see motion. Which is good, 'cause if they could, they’d clean up at the racetrack.


If there is only one photon in a universe, then the radius of that universe expands at the speed of light, as the region where the photon might exist to interact with another object expands. Since the space defined by that radius cannot experience any change, the speed of light cannot be defined as less than infinite. (There is no here, or there, and no now or then.) I think the symmetry of the described universe’s vacuum increases, though, and that might cause inevitable quantum instability.

I could be wrong about that.

Don’t try this at home.


“It should be possible to explain the laws of physics to a barmaid.” ~ Albert Einstein ~

“You should see the place where Einstein used to drink!” ~ Triskadecamus ~

This answers my question.
A photon just can’t have a frame of reference.
That creates a paradox.
So we just say it can’t have.

Thanks for the answers people.