electromagnetic fields and empty space


by nouveau_riche
Tags: electromagnetic, fields, space
nouveau_riche
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#1
Jul25-11, 10:36 AM
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is it possible for electromagnetic field to exist without matter?
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#2
Jul25-11, 12:06 PM
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Yes, it is.
That's one of the particulars of 20th century physics.
People have thought for a long time that electromagnetic fields should propagate through some medium, in the same way that water waves or sound do. To explain EM waves propagating through vacuum they invented the concept of something called ether, permeating throughout space.
Ironically the experiment of Michaelson and Morley, which intended to prove the existence of that substance, was one of the major factors in discarding it.
Drakkith
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#3
Jul25-11, 01:47 PM
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Yep! Just look at a photon!

timthereaper
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Jul25-11, 02:16 PM
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electromagnetic fields and empty space


Doesn't the EM field require the existence of charged particles to form?
ecneicS
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#5
Jul25-11, 02:31 PM
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light isn't a charged particle but it is an oscillating ripple in the EM field. But I couldn't tell you why.
mathfeel
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#6
Jul25-11, 03:57 PM
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I think what OP wants to know is that electromagnetic wave can propagate without a medium, but can you create them without charged matter somewhere. Yes, You need some oscillating charge somewhere to create them, except maybe for fluctuation of the vacuum.

On the other hand, one predicted death of the universe is that everything, including proton, decays to photons so far away from each other that they never interact. So I suppose that'd be the case of photon without matter.
Drakkith
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#7
Jul25-11, 05:42 PM
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Quote Quote by timthereaper View Post
Doesn't the EM field require the existence of charged particles to form?
Quote Quote by mathfeel View Post
I think what OP wants to know is that electromagnetic wave can propagate without a medium, but can you create them without charged matter somewhere. Yes, You need some oscillating charge somewhere to create them, except maybe for fluctuation of the vacuum.

On the other hand, one predicted death of the universe is that everything, including proton, decays to photons so far away from each other that they never interact. So I suppose that'd be the case of photon without matter.
Remember that according to current science, the universe itself was once all photons. So where did those photons come from if they needed charged particles to create them?
DaleSpam
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#8
Jul25-11, 06:00 PM
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In principle it would be possible to have a universe with no charges, but with radiation. The early universe was radiation-dominated.

Edit: looks like Drakkith beat me to it!
Dotini
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Jul25-11, 06:21 PM
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Quote Quote by DaleSpam View Post
In principle it would be possible to have a universe with no charges, but with radiation. The early universe was radiation-dominated.
The early universe was dominated by ionizing radiation, wasn't it? So charge must have preceded matter.

Respectfully,
Steve
DaleSpam
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Jul25-11, 08:14 PM
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Quote Quote by Dotini View Post
The early universe was dominated by ionizing radiation, wasn't it? So charge must have preceded matter.
The phrase "ionizing radiation" just refers to radiation of sufficiently high energy that it could ionize an atom. It by no means implies anything about its origin.
nouveau_riche
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#11
Jul26-11, 05:48 AM
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Quote Quote by Drakkith View Post
Remember that according to current science, the universe itself was once all photons. So where did those photons come from if they needed charged particles to create them?
i asked for electromagnetic fields to exist without matter,that itself excludes photon
Drakkith
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Jul26-11, 06:03 AM
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Quote Quote by nouveau_riche View Post
i asked for electromagnetic fields to exist without matter,that itself excludes photon
How so? Photons ARE electromagnetic fields. Or rather oscillations in them or whatever. If photons existed before matter then that is an example of EM fields existing without matter.
nouveau_riche
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#13
Jul26-11, 06:13 AM
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Quote Quote by Drakkith View Post
How so? Photons ARE electromagnetic fields. Or rather oscillations in them or whatever. If photons existed before matter then that is an example of EM fields existing without matter.
because photon itself is matter
Drakkith
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#14
Jul26-11, 06:26 AM
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Quote Quote by nouveau_riche View Post
because photon itself is matter
No, photons are not matter. They are electromagnetic radiation.
mikeph
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#15
Jul26-11, 06:59 AM
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Quote Quote by DaleSpam View Post
In principle it would be possible to have a universe with no charges, but with radiation. The early universe was radiation-dominated.
Hold on- at sufficiently high temperatures there is the matter-antimatter-radiation equilibrium, and when the temperature drops, matter and antimatter combine to form radiation and whatever is left. It's at this point that you look and see that there are many more photons than protons/electrons, and conclude "the early universe was radiation dominant"...

Radiation dominant doesn't mean there wasn't matter, simply that the matter/antimatter difference was so slight that when they combined, most of the matter was converted to radiation, leaving a small amount of matter, and a relatively large amount of radiation (dominant == considerably higher energy density).

I don't believe radiation dominant can be used for an argument that the electromagnetic field can exist without there ever previously being any charge present. That radiation came from charge/anticharge interactions in the first place.
nouveau_riche
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#16
Jul26-11, 09:49 AM
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Quote Quote by Drakkith View Post
No, photons are not matter. They are electromagnetic radiation.
so what makes matter as matter?how can photon exist without existence of matter?
Dotini
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#17
Jul26-11, 10:17 AM
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Quote Quote by nouveau_riche View Post
so what makes matter as matter?how can photon exist without existence of matter?
Maybe photons would exist, but would you know it unless it had a material surface to light up?

I see electrons, protons and other subatomic particles coming together from the regime of ionizing radiation to form atoms and molecules.

Respectfully submitted,
Steve
chrisbaird
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#18
Jul26-11, 10:33 AM
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Quote Quote by nouveau_riche View Post
so what makes matter as matter?how can photon exist without existence of matter?
"Matter" in physics is any object or particle that has mass. Photons have no mass and are not considered matter. If you want to use the word "matter" to describe anything that exists or can exist, massive and massless, then the word becomes useless.


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