Photon Questions: Atom-Atom Travel & Purpose

[Darken-Sol]

are there photons traveling from every atom to every other atom in the universe? hypothetically, if i were standing on an atom and i looked in any direction at another atom would i be able to see it? also what purpose does a photon have besides carrying information?

 

[Darken-Sol]

should have went to wiki first. last question answered. i can't find an answer to the first question though. and the second was just to describe my line of thinking.i didnt understand the absorbing and emitting. is there always the same number of photons? it seems unlikely since most of them are heading away from everything.

 

[Drakkith]

Photons are emitted in finite quantities, generally in a random direction from an atom, and not towards any specific atom.

 

[Darken-Sol]

Photons are emitted in finite quantities, generally in a random direction from an atom, and not towards any specific atom.

an atom was a poor choice i was trying to simplify my thought. i have trouble getting answers because i lack the terminology everyone uses. from any frame of reference, does every atom send photons my way?i mean i can see every thing in this room. i find it absurd to think one big table photon is how i see a table.

 

[BillSaltLake]

There are ~10⁸⁰ atoms and ~10⁸⁹ photons in the observable universe. Your scenario would require ~ 10¹⁶⁰ photons.

 

[Darken-Sol]

There are ~10⁸⁰ atoms and ~10⁸⁹ photons in the observable universe. Your scenario would require ~ 10¹⁶⁰ photons.

how did u come across those numbers?

 

[DaveC426913]

does every atom send photons my way?i mean i can see every thing in this room. i find it absurd to think one big table photon is how i see a table.

If the room were completely dark, then there would be no external source of photons impinging on the atoms of the table. If the table were near absolute zero, then it would be emitting virtually no photons in the form of black body radiation.

Normally though, neither of the those conditons are true.

The table has been irradiated with heat from a room tempature environment, so it is continually abosrbing and remitting photons, a portion of which are in the infrared range.

The table is also in a lighted room, meaning it is constantly being bombarded by photons from the lgiht source, and is merely reflecting those photons. Turn up brightness of the lights, and more bombardment by photons and more re-emission of them from the object (i.e. it is easier to see).

How many photons?

Here's an article that talks about it.
http://zfacts.com/p/791.html

Basically, a candle, even at .0017 watts, emits enough light for millions to billions of photons to enter your eye every second.

And here's another that says in the room you're in right now (assuming it has a single bulb emitting 25-watts of visible light) there are on the order of one hundred billion photons.
http://scienceblogs.com/builtonfacts/2009/03/counting_photons.php

Photons are massless, chargeless and bosonic - many can occupy the same volume of space simultaneously.

 

[Darken-Sol]

a photon from a star is traveling to my eye. if this photon gets absorbed by a speck of dust on the way, it then reemits as a (speck of dust) photon? or it wings of in a random direction and i never see it.

 

[Drakkith]

a photon from a star is traveling to my eye. if this photon gets absorbed by a speck of dust on the way, it then reemits as a (speck of dust) photon? or it wings of in a random direction and i never see it.

If an atom in that dust absorbs the photon, it will most likely emit another photon (not the same one) in a random direction. It is POSSIBLE that emitted photon from the dust could continue in the same direction, but very very unlikely. The ways that atoms absorb and emit light is fairly complicated and you would need to get into quantum mechanics to accurately describe them.

 

[DaveC426913]

a photon from a star is traveling to my eye. if this photon gets absorbed by a speck of dust on the way, it then reemits as a (speck of dust) photon? or it wings of in a random direction and i never see it.

Effectively, the absorption and emission are to be treated separately. Regardless of how it absorbs photons, it will simply emit photons in a random direction as blackbody radiation.

 

[BillSaltLake]

See
http://en.wikipedia.org/wiki/Observable_universe
for # of atoms. Photon:baryon ratio is ~ 10⁹. This ratio hasn't increased much due to hot objects (stars) emitting photons.

 

[Darken-Sol]

after a bit more studying i have more questions.
what happens to a photon at rest? or they don't rest?
if they are affected by gravity can we cause one to orbit something? besides a black hole?
if a photon is entangled what is the limit of messing with it and getting results for its partner?

 

[DaveC426913]

after a bit more studying i have more questions.
what happens to a photon at rest? or they don't rest?
if they are affected by gravity can we cause one to orbit something? besides a black hole?
if a photon is entangled what is the limit of messing with it and getting results for its partner?

1] Photons always travel at c.
2] It is sort of possible to get photons to orbit a BH, but the orbit is not stable. (Photons aren't subject to losing velocity as they climb away from a gravity well, so an elliptical obrit won't work. You'd have to make it circular.)
3] Entanglement is a whole nother kettle of wax...

 

[Darken-Sol]

1] Photons always travel at c.
2] It is sort of possible to get photons to orbit a BH, but the orbit is not stable. (Photons aren't subject to losing velocity as they climb away from a gravity well, so an elliptical obrit won't work. You'd have to make it circular.)
3] Entanglement is a whole nother kettle of wax...

i read somewhere photons travel at c in a vacuum, but they can be slowed in a medium.
i was wondering if we could send an entangled photon into a black hole and collect data from the other one.

 

[BillSaltLake]

A photon has to keep moving or it dies, just like sharks. [OK not exactly like sharks.]

 

[Darken-Sol]

A photon has to keep moving or it dies, just like sharks. [OK not exactly like sharks.]

but where does the energy go?

 

[BillSaltLake]

Bit of a joke above. The momentum is proportional to the energy of a photon in free space. These are proportional to 1/a, where "a" is the expansion parameter. In free space, a photon always travels at c with respect to any local frame regardless of how much stretch has occurred (i.e., how big a has become). The energy just disappears in that it does not flow anywhere. The energy loss is equivalent to putting a group of blackbody photons in a perfectly reflective cube with (increasing) side length "a". The increase will redshift the photons inside.

 

[DaveC426913]

i was wondering if we could send an entangled photon into a black hole and collect data from the other one.

Entanglement cannot be used to transmit information.