# Photon?

Discussion in 'Physics & Math' started by Fredrik, Jan 2, 2015.

1. ### FredrikRegistered Member

Messages:
2
If a photons energy is calculated by taking Plancks konstant and multiplying it with it's velocity, then doesn't than mean that if a photon were to go through Earth's atmosphere, the energy would decrease since the it's slowing down which shouldn't be possible right?

Also if elektromagnetism is essentially photons then why don't electromagnetic materials emit light?

3. ### Russ_WattersNot a Trump supporter...Valued Senior Member

Messages:
5,051
Fredrik likes this.

5. ### exchemistValued Senior Member

Messages:
6,854
Since Russ has answered the first part, I'll have a pop and the second.

Photons are electromagnetic (EM) radiation. Any electric charge that oscillates will radiate EM waves, that is, it will emit photons. A good example is a radio antenna, in which electrons oscillate at the frequency of the radio emission and thereby induce radio-frequency photons to be emitted. You can't see these photons of course, because they have a wavelength that is far too long to be what we call "light". Another example is the electrons in an atom. When one of these drops from a higher energy orbital to a lower energy one, it creates an oscillating dipole that emits a photon, which may well be visible as light, since the frequency of this process is far higher than that of the electrons moving in a radio antenna. Sodium street lamps use this principle (the yellow is due to the famous "sodium D line", caused by excited sodium atoms emitting photons with the frequency of yellow light.)

So in a way electromagnetic materials do emit light, but you have to be careful what you mean by an "electromagnetic material". It needs to be something with moving electric charges.

Fredrik likes this.

7. ### zxenRegistered Member

Messages:
21
Human Retinas perceive a certain part of the electromagnetic spectrum. We call this light. Animals such as sharks can perceive things like metal, and bats can see sound. Apparently dogs can smell in 'colour'. Charles Darwin proposed that over hundreds of years, certain traits were kept if successful individuals of a species didn't die in bad conditions such as droughts, famines and ice ages etc, and were able to find a mate to transfer their unique DNA into new offspring. Charles Darwin proposed that these changes occurred randomly or through selective breeding. But quantum physics seems to indicate that there is a fifth force of nature that still seems magical to us at this point in history: Mind. We can change matter at a subatomic level just by concentrating on it, or in the case of plants, perhaps another mind makes a plant figure out how to suck the blood out of flies or make prettier flowers. The electromagnetic force, to which human-perceived light belongs, travels at various speeds through various materials, especially the main material of the universe, primitively known at this point in history simply as 'the fabric of spacetime'. If the gravity is low, the electromagnetic force travels slower. And vice versa. Light travels fastest in a black hole. Also look at red shifting effects of galaxies. Materials such as liquid slow it down, and solids stop a lot of it from penetrating at all, which is why you can't see through walls. But rest assured, the photons (electromagnetic radiation) will still eventually tear a hole through the American flag on the moon. Radio waves and x rays can penetrate a certain amount of solid material. I'm basically giving you layperson responses here. Hopefully someone will correct me. I think that electromagnetism and all forces might work by rippling along the fabric of spacetime from one location in the universe to another. This might mean that the fabric has a density that we cannot compare to the outside of the universe. The fabric is not empty and uniform either. Its foaming matter/energy out of itself all the time.

Fredrik likes this.
8. ### FarsightValued Senior Member

Messages:
3,475
The photon energy is E=hf, where f is frequency. The photon doesn't slow down as it goes through the atmosphere. However the "coordinate" speed of light is lower at a lower elevation, so in a way the photon goes slower as it gets lower. See this Baez article for more on that. However it doesn't lose any energy. Instead it appears to gain it, wherein we talk of "blueshifted" photons. But: it doesn't actually gain any energy. There is no magical mechanism by which a photon gains energy from something else. Gravity is not a force in the Newtonian sense. Conservation of energy applies. What happens is that you and your clocks go slower when you're lower, so you measure the self-same photon frequency to be higher. It's a bit like what happens if you accelerate towards a photon in free space. You measure it to be blue-shifted, but the photon didn't change a bit. Instead, you did.

They do. But you have to heat up some material to make it emit light you can see. Strike a match, and you can see an electromagnetic material emitting light.

Messages:
2

10. ### krash661[MK6] transitioning scifi to realityValued Senior Member

Messages:
2,973
it's wise to ignore farsight.

11. ### James RJust this guy, you know?Staff Member

Messages:
30,835
Fredrik:

Probably you have seen the equation $E=h\nu$ for the energy of a photon. The second symbol on the right-hand side is not a $v$ for velocity. It's a Greek letter: 'nu', which in this context is used to represent the photon frequency.

The speed of light in air is almost the same as in vacuum, so photons don't slow down very much at all when they enter Earth's atmosphere.

Also, when a photon goes from one medium to another - say from air into water, it's frequency doesn't change, even though the speed of light and the wavelength both change. So, the photon energy remains constant.

They do - under the right conditions.

But I'm not quite sure what you mean by an "electromagnetic material". What would be an example of such a material?

It is important to appreciate that the emission and absorption of light (photons) is only one kind of electromagnetic phenomenon. There are many kinds of electrical, magnetic and electromagnetic effects that don't involve photons*.

*Or at least not real photons, but let's not get into that yet.

Aqueous Id likes this.
12. ### James RJust this guy, you know?Staff Member

Messages:
30,835
Farsight,

Actually, there's no way to tell the difference, since there are no preferred reference frames. A technical point, which I'm sure you understand.

13. ### FarsightValued Senior Member

Messages:
3,475
Sorry, I don't know what you mean James. Maybe it would be clearer if I replaced the photon with a star: when you accelerate towards it, the starlight appears blueshifted. But it hasn't changed, instead you have.

14. ### QuarkHeadRemedial Math StudentValued Senior Member

Messages:
1,532
Here again, Farsight, you pose yourself as a "relativity denier". ALL relativistic theories - yes, even Galileo's - make no distinction between a hypothetical "you" at rest and the star moving toward you on the one hand, and the star at rest and the hypothetical "you" moving toward it on the other.

In either case - which is a silly way to frame it, as the 2 situations are relativistically equivalent - the star's light is blue shifted. And if there is no way to to sure who exactly is doing the moving, the statement that "it was you that changed, not the star" lacks content in any relativistic theory.

I wonder what Einstein would have said - do you have a (partial) quote, Farsight?

Messages:
21,703

Mis-placed confidence James old matey!

16. ### James RJust this guy, you know?Staff Member

Messages:
30,835
Ah. I overestimated you, it seems.

There's no way to tell whether you're moving towards a star or whether it is moving towards you. Only relative motion matters when it comes to blue shift. So once the period of acceleration is over and we've settled down to a constant relative velocity, there's no way to know which party did the accelerating (i.e. who changed and who didn't).

17. ### FarsightValued Senior Member

Messages:
3,475
I'm not a relativity "denier". There's a clear distinction in that you accelerated, and you could feel it. You know you changed. And you know the star didn't change just because you put the pedal to the metal. You know that your observation of it changed.

Garbage! It's crystal clear who's doing the moving! And we can observe that the star didn't change one iota just because you decided to accelerate towards it.

No. This is simple stuff.

I doubt it.

You felt the acceleration, you can see the star getting bigger in your viewscreen while Sol is getting smaller in your rear-view mirror. You know full well you're moving towards it. Along with everybody else who's been watching you.

18. ### Dr_ToadIt's green!Valued Senior Member

Messages:
1,847
Why is Farsight allowed to post in any sections here except alt theories? For that matter, why is he allowed here at all?

19. ### Beer w/StrawTranscendental Ignorance!Valued Senior Member

Messages:
3,575
Because Farsight is a real man!

20. ### FarsightValued Senior Member

Messages:
3,475
Because of all the people here, my physics knowledge is the best.

Why are you allowed here at all? You're just a troll.

21. ### OnlyMeValued Senior Member

Messages:
3,914
When did you FEEL or measure your acceleration relative to any star? As far as any velocity we have relative to any star, we are part of an inertial system dominated by the earth's graviationnal field. Any acceleration you feel is realive to the earth or at best if you ever made it into space, perhaps our sun.

Come on Farsight, you are confusing what you imagine as a hypothetical situation and reality. I mean Einstein, your hero produced a convincing argument against you current position in 1905, when he introduced special relativity.., and he was really consolidating evidence and theory that predated his insights.

Aqueous Id likes this.
22. ### krash661[MK6] transitioning scifi to realityValued Senior Member

Messages:
2,973
says the one who never stepped into an actual scientist lab(s). says the one who never ever touched science through experiments or models. says the one who never touched higher levels of physics. says the one who continues to incorrectly interpret everything. says the one who continues to deceive when confronted . it's referred to as experience as an actual scientist, not some typical inexperienced piss-ant.

Aqueous Id likes this.
23. ### PhysBangValued Senior Member

Messages:
2,422
Then why have you never, in about a decade of posting, produced an equation to support your claims? Why have you insulted the efforts of scientists by claiming that they calculate things correctly, but you never point out the error in calculation?

I submit that you are a liar.

Aqueous Id and paddoboy like this.