Matter-energy equivalence ?


by big_bounce
Tags: equivalence, matterenergy
big_bounce
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#1
Feb13-13, 03:06 PM
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Hello all .

Is the paragraph right ?

Introduction – Energy from Matter
E=mc2

Einstein's famous equation from 1905 E=mc2 demonstrates that energy (E) is equivalent with matter (mass m). It suggests that the concept of mass is indeed, less basic than what can be believed from everyday experiences with massive bodies. In fact, energy can be transformed into massive particles, and mass can be transformed into energy. Energy in all its different appearances is a key concept in physics.

I think there are three mistakes in the sentences .

First mistake is that mass and matter is not same and the text is not right .

Einstein's famous equation from 1905 E=mc2 demonstrates that energy (E) is equivalent with matter (mass m) .

Second mistake is that energy can not transform to massive particles but it can convert to massive particles , because massive particles are not made of energy .


Third mistake is that mass_energy are equivalence not matter_energy .

Energy and matter are equivalent.
What's your idea ?
http://www.nobelprize.org/educationa...rgy/intro.html
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mathman
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Feb13-13, 03:16 PM
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Off hand, I think you are quibbling.
For example saying mass is equivalent to energy is NOT the same as mass is the same as energy.
What distinguishes "transform" from "convert"? You seem to think the first is wrong but the second is correct.
PeterDonis
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Feb13-13, 03:20 PM
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Quote Quote by big_bounce View Post
First mistake is that mass and matter is not same and the text is not right.
It depends on how "mass" and "matter" are defined. See below.

Quote Quote by big_bounce View Post
Second mistake is that energy can not transform to massive particles but it can convert to massive particles, because massive particles are not made of energy.
Yes, they are, because mass and energy are equivalent if defined properly. Again, see below.

Quote Quote by big_bounce View Post
Third mistake is that mass_energy are equivalence not matter_energy.
Ah, so mass and energy *are* equivalent. That means massive particles *are* made of energy.

I think what the page is (somewhat clumsily) trying to say is that particles with nonzero rest mass (what we normally call "matter") and particles with zero rest mass (what we normally call "radiation" but could also call "energy") can be inter-converted by nuclear reactions. For example, an electron and a positron can annihilate each other and produce photons; or a pair of photons can produce an electron-positron pair. Or, even if the nuclear reaction involves only particles with nonzero rest mass, some of the initial rest mass can be converted into energy, this time appearing as the kinetic energy of the reaction products. For example, if a uranium nucleus at rest fissions, the fission products are both massive particles (they are nuclei of lighter elements), but they will have a large kinetic energy, because the rest mass of the uranium nucleus is larger than the sum of the rest masses of the fission products; the difference appears as kinetic energy.

If we ask questions like, how much energy would be in the photons produced if an electron and positron annihilated each other? or, how much kinetic energy do the fission products have if a uranium nucleus fissions? the answers are given by the formula E = mc^2. So that formula, in a sense, gives a "conversion rate" between matter and energy in nuclear reactions. The point being, of course, that c^2 is a very large number, so a small quantity of matter can release a large quantity of energy in a nuclear reaction.

big_bounce
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#4
Feb13-13, 03:26 PM
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Matter-energy equivalence ?


Quote Quote by mathman View Post
Off hand, I think you are quibbling.
For example saying mass is equivalent to energy is NOT the same as mass is the same as energy.
So if they aren't be same , can we say matter and energy are equivalent ?


Quote Quote by mathman View Post
What distinguishes "transform" from "convert"? You seem to think the first is wrong but the second is correct.
Energy exists in many forms and one of them is mass So energy can be transformed to mass not to matter .

Albert Einstein showed that ultimately all matter is capable of being converted to energy, by the formula:
E = mc^2

http://en.wikipedia.org/wiki/Matter
PeterDonis
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#5
Feb13-13, 03:31 PM
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Quote Quote by big_bounce View Post
So energy can be transformed to mass not to matter.

Albert Einstein showed that ultimately all matter is capable of being converted to energy
I agree with mathman here, you seem to be contradicting yourself; first you draw a distinction between "mass" and "matter", then you obliterate it by saying matter can be converted to energy.

IMO a better strategy is to forget about terminology ("mass" vs. "matter" or "energy") and focus on physics. I described the relevant physics in my last post.
Drakkith
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Feb13-13, 04:01 PM
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It seems to me that one must be very careful when saying that mass and energy are the same things, or that matter is made of energy. In certain situations energy and mass are equivalent, and you can transform one to the other, and it's true that matter can be "converted" to energy, but the reality is far more complicated than those simple statements in my opinion.
pervect
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#7
Feb13-13, 04:59 PM
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My $.02. The above text isn't awful, but can be improved.

Introduction – Energy from Matter
E=mc2

Einstein's famous equation from 1905 E=mc2 demonstrates that energy (E) is equivalent with matter (mass m).
This is confusing. Is "matter" supposed to be the same as "mass m". What does equivalent even mean?

My first take at changing this would be:
Einstein's famous equation from 1905 E=mc2 gives a formal relation between mass, and energy.
Moving on:
It suggests that the concept of mass is indeed, less basic than what can be believed from everyday experiences with massive bodies.
This is pretty much spot on. I might expand it by pointing out that there are several concepts of mass in general relatvity.

A literature reference with a roughly similar point of view might help: such as Hecht's http://dx.doi.org/10.1119/1.2150758 "There is no really good defintion of mass". I have a feeling that Hech'ts qrticle needs to be "balanced" with some other points of view, I'm not quite sure what to suggest though.

My own view is that the problem isn't really that there is no good definition of mass, it's that there's too many not-bad definitions.

In fact, energy can be transformed into massive particles, and mass can be transformed into energy. Energy in all its different appearances is a key concept in physics.
This is pretty much spot on too. I might add some remark about how the actual conversion (under some cirumstances) suggests that the relation between energy and mass is more than just formal. It'd probably be best to leave it at this level of indifiniteness, under the principle of "Never write more clearly than you can think".
big_bounce
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#8
Feb13-13, 06:00 PM
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Quote Quote by PeterDonis View Post
Yes, they are, because mass and energy are equivalent if defined properly. Again, see below.

Ah, so mass and energy *are* equivalent. That means massive particles *are* made of energy.
If meaning of massive particles is all known particles which have non-zero rest mass like electron or positron , i am not agree with you by refer to the post

http://www.physicsforums.com/showpos...42&postcount=9

Please see that and say what are you think about it ?
Drakkith
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Feb13-13, 06:22 PM
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Quote Quote by big_bounce View Post
i am not agree with you by refer to the post
I don't want to be rude, but this statement borders on being incomprehensible.
Is English your first language, or do you have another?
big_bounce
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#10
Feb13-13, 06:42 PM
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Quote Quote by Drakkith View Post
I don't want to be rude, but this statement borders on being incomprehensible.
Is English your first language, or do you have another?
Not first and not even second . Sorry for my English
Drakkith
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Feb13-13, 06:46 PM
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Quote Quote by big_bounce View Post
Not first and not even second . Sorry for my English
Ah, ok.

And by the way, the post you linked, which I will link below, is exactly what I meant in my earlier post.

http://www.physicsforums.com/showpos...42&postcount=9
PeterDonis
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Feb13-13, 07:24 PM
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Quote Quote by big_bounce View Post
If meaning of massive particles is all known particles which have non-zero rest mass like electron or positron , i am not agree with you by refer to the post

http://www.physicsforums.com/showpos...42&postcount=9

Please see that and say what are you think about it ?
Please bear in mind that I was basing what I said on what you said; you were the one who said mass and energy were equivalent. I didn't mean to imply that I was necessarily taking the same view. I agree with Drakkith that things are more complicated than that; if you think so too, then we are all in agreement.

I described some of the complexities in my earlier post when I talked about nuclear reactions. In my opinion, it's better to focus on the physics--what nuclear reactions are possible, what particles participate in them, and what energy changes are involved--than to worry about what is "made of" what or what is "equivalent" to what.
danR
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#13
Feb13-13, 10:05 PM
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Quote Quote by pervect View Post
My $.02.
$.02 is equivalent to 2˘.

They are equivalent. They are not the same thing.

Maybe that will be a good first approximation of an analogy.

My 2˘ worth.
Chronos
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#14
Feb13-13, 11:22 PM
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Collider experiments have long since confirmed the mass-energy equivalence principle. So, what exactly do you find objectionable about that?
mathman
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#15
Feb14-13, 03:45 PM
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Mass is a quantitative term while matter is generic. When two protons collide in the LHC, matter is converted to energy. Mass is used for bookkeeping purposes. The total outgoing mass + energy must add up the incoming mass.


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