Wudang
BOFH
Photons are massless. Does that help?
XiaoLaoHu said:Thank you for the link. That will keep me busy reading for few days.
You're welcome and as I should have said in my post - welcome to the forum.
HarryKeogh
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CurtC
Illuminator
Photons have zero rest mass, which is a hypothetic thing, since a photon (by definition) is always moving at the speed of light. A photon does have momentum.Wudang said:
phildonnia
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Just to be pedantic,
It may be misleading to speak of "energy containing mass" or "matter containing energy" or "converting matter to energy".
Matter is energy, they are the same thing.
Matter/Antimatter annihilation is an example of converting energy in one form (electrons and positrons, say) into another (high-energy photons).
It may be misleading to speak of "energy containing mass" or "matter containing energy" or "converting matter to energy".
Matter is energy, they are the same thing.
Matter/Antimatter annihilation is an example of converting energy in one form (electrons and positrons, say) into another (high-energy photons).
Yes, energy has mass.Originally posted by XiaoLaoHu
Does energy contain mass?
If it does not, why E=mc²?
What does it mean to say that something has mass? It means that the thing is heavy: if we put it on a scale, the scale will show that its weight is not zero.
How can we put energy on a scale to see if it has weight? Well, energy comes in lots of different forms, but here's one example. To compress a spring, we need to do work on it. Therefore, a spring contains more energy when it's compressed than when it isn't compressed. So it will weigh more when it's compressed. (For a spring, the difference in weight is tiny and probably too small actually to detect, but in principle a compressed spring does weigh more. In other cases, the difference is detectable. See this old thread, for example.)
I'm not very happy with the first two answers in that "Ask a Scientist" link. Photons certainly are attracted by gravity. From Einstein's book on relativity, appendix 3, section (b) "deflection of light by a gravitational field":<blockquote>according to the general theory of relativity, a ray of light will experience a curvature of its path when passing through a gravitational field, this curvature being similar to that experienced by the path of a body which is projected through a gravitational field.</blockquote>That's pretty clear, I'd say.
Your first question was easier.
Helmholtz's explanation is long, but good.
(The article contains an unfortunate typo in paragraph 25: "A single labourer would not be able to raise the load ... " should instead be "A single labourer would now be able to raise the load ... ". Also, it often uses the word "force" where we would nowadays use the word "energy"; it was written 140 years ago, and terminology changes. Also, relativity hadn't been developed yet, so it doesn't talk about the equivalence of mass and energy; it just deals with energy alone.)
Let me know if you conclude the answer is any better than 'Duh, we dunno what "Energy" is', or 'goddidit'.XiaoLaoHu said:Thank you for the link. That will keep me busy reading for few days.
Hmm, maybe one of those "emergent properties", huh? LOL.
I think a simple comment is called for here.
Mass and energy can be related by the E=mc^2 relationship.
You can change mass into energy and vice versa.
If you look at the elements, look at the weight of, say, a Hydrogen atom vs. the weight of its constituants, and then look at the weight of an Iron 56 atom vs. its constituants, you can see energy converted into mass right there.
If you look at heavy elements, you'll see a different effect, say for lead, comparing the weight of one of its isotopes to the weight of its constituant particles. You'll see that the isotopes are barely, just barely stable, because it takes energy to make the nucleii, instead of taking energy to separate them like it does for Iron.
Mass and energy can be related by the E=mc^2 relationship.
You can change mass into energy and vice versa.
If you look at the elements, look at the weight of, say, a Hydrogen atom vs. the weight of its constituants, and then look at the weight of an Iron 56 atom vs. its constituants, you can see energy converted into mass right there.
If you look at heavy elements, you'll see a different effect, say for lead, comparing the weight of one of its isotopes to the weight of its constituant particles. You'll see that the isotopes are barely, just barely stable, because it takes energy to make the nucleii, instead of taking energy to separate them like it does for Iron.
Just thinking
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Re: Re: Does energy contain mass?
Ahhh, this can become somewhat subjective, as General Relativity suggests that gravity warps space-time in such a way that light (and other objects) always travel along what they perceive as a straight line in space-time. So it begs the question, is it a mass-mass gravitational interaction or is light just following a curved road?
69dodge said:
Ahhh, this can become somewhat subjective, as General Relativity suggests that gravity warps space-time in such a way that light (and other objects) always travel along what they perceive as a straight line in space-time. So it begs the question, is it a mass-mass gravitational interaction or is light just following a curved road?