# What is a photon

#### yyttr2

I didnt know were to post this so it just goes here :).

(btw I'm in 9th grade so complexity is not an option.)

photons have zero mass, and zero rest energy.
are they a wave? or a partical?
If it has zero mass how can it be anything at all?
If its a partical, how can it exist without mass?
If there a wave...well, wtf is a wave without particals?

I have been studying chemistry and it is these questions, or ones similar to them that make me wont to stab something.

trying to understand atomic orbitals and electron configuration is easy. untill you start trying to understand how N,L, and m changes the shapes,sizes, and orientation of orbitals.
and why m doesnt only change the orintation
i.e.
n3l2m0
is 2 balls with a ring around it but.
n3l2m1
is four balls.

I might be stupid and the answer be simple and easy but for the moment I am frustrated as hell!

forgive spelling errors

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#### Pythagorean

Gold Member
they're wave packets!

what?

#### Pythagorean

Gold Member
it doesn't have zero mass, just zero rest mass

#### yyttr2

but...then, what happens if an photon stops moveing?...

#### Pythagorean

Gold Member
but...then, what happens if an photon stops moveing?...
it doesn't necessarily "stop moving". It can be absorbed by another particle like an electron, but it always travels at the speed of light.

Gold Member

#### Blenton

Surely when it gets absorbed it must decelerate.

#### yyttr2

how can a partical absorb another partical?...
Things I cannot visualize tend to confuse me.

#### DaveC426913

Gold Member
Do not attempt to apply common sense or classical physics to the subatomic world. You are entering a realm where there is no analogy. You've got to accept the physics at face-value.

The best thing to do is to pick up a good book on the subject to flood yourself with the ideas. Frankly, the terse answers we can provide here will only serve to confuse you further.

But https://www.physicsforums.com/showpost.php?p=867751&postcount=3" that may get you started.

Last edited by a moderator:

#### Bob S

In a hydrogen atom, when an electron falls from a n=3, L=2 state to a n=2, L=1 state, the atom emits a small packet of visible light. It takes a few nanoseconds for the emission to take place, so this is the extent of the length of the wave packet (1 foot = 1 nanosecond, more or less). The packet contains energy and momentum, and always travels at the speed of light.

#### keora13

A photon is like a packet of energy. We describe it like a particle because that's the only way we can use it in a meaningful way in physics. Because a photon is energy, it can be absorbed by other particles.

A photon is the only thing that can travel at the speed of light, because it has no mass (you will learn later in Special Relativity that only objects that have no mass can actually travel at the speed of light. This is because the faster something goes, the heavier it becomes).

Hope that clears something up for you

#### cragar

Photon is not the only thing that can travel at the speed of light , the graviton can and maybe the Tachyon and maybe some others that i havn't listed.

#### DaveC426913

Gold Member
Photon is not the only thing that can travel at the speed of light , the graviton can and maybe the Tachyon and maybe some others that i havn't listed.
No and no.

Gravitons have never been detected and are only theoretical at this point.

Tachyons cannot travel at the speed of light. They are massive particles (just like our electrons and protons), that travel FASTER than the speed of light, and cannot slow down TO the speed of light, or less than.

Additionally, tachyons are merely hypothetical particles. There's no reason to believe they exist at all, it's just that relativity doesn't explictly rule them out.

#### cragar

fine gravity waves travel at the speed of light , but y can't i believe in graviton's
the standard model has a very good track record.

#### DaveC426913

Gold Member
fine gravity waves travel at the speed of light , but y can't i believe in graviton's
the standard model has a very good track record.
I didn't say you couldn't, it's just that they have yet to be detected.

#### cragar

are u saying that the photon is the only thing that travels at the speed of light.

#### carlsjo

Mass and energy are two forms of the same thing. It just so happens that the a photon has no mass, but it's energy can be related to mass by E=mc^2 (Einstein's mass/energy relation).

Everything moves in waves (DeBrolie principle), although you cannot notice the waves of objects that we can see like a baseball.

The smaller a object is the larger the wave it makes when in motion. Visible light are photons and because they are so small, their waves are much bigger than a baseball's. In fact, you can see photon waves by shinning light through a pin-hole or small slit.

#### Naty1

Trying reading Wikipedia under LIGHT and, separately, PHOTON...you'll pick up some interesting ideas.

In classical physics light is sometimes described as a "particle" or an electromagnetic wave and in quantum mechanics as a "quantum". You'll find we have decent mathematical models to describe how things like light behave, but are not so got at describing what they actually are.

Electron orbits, which you mention in your post, are also a simplified behaviorial description when in fact an electron is not really a particle...at least not all the time....

The point is nobody knows exactly what an electron or photon is...nor precisely how they got here....The only "simple" answers in physics are superficial...the real interesting ones are quite baffling!!!!

#### lightarrow

A photon is the only thing that can travel at the speed of light, because it has no mass (you will learn later in Special Relativity that only objects that have no mass can actually travel at the speed of light. This is because the faster something goes, the heavier it becomes).
Well, even if we still haven't detected gluons, these are massless particles and so they travel at c.

#### cragar

gravity travels at c and im pretty sure we have detected that.

#### cragar

No and no.
Gravitons have never been detected and are only theoretical at this point.
are u saying the gravity does not have an associated particle.

#### Researcher X

are u saying the gravity does not have an associated particle.
Nobody knows. It doesn't have to.

#### cragar

Qm says for every field there is an associated particle , ya i mean we dont really know
, but we have a good idea that it does.

#### physical1

Qm says for every field there is an associated particle , ya i mean we dont really know
, but we have a good idea that it does.
What if the whole idea of "Particle" is just man made macroscopic abstraction? Like how God was a man made idea and may be a false visualization? What if there are no such things as actual "particles"? What if there are just invisible globs of universal magic which sometimes can be created and destroyed (photons) but sometimes not (electrons)?

Rhetorical questions :-)

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