| smiley_face
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| 124834. Thu Dec 07, 2006 5:55 pm |
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I still don't get this mass=energy business.
It's just doing my head in! I shall stick to biology I think, at least it partly makes sense. |
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| Jenny
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| 124874. Thu Dec 07, 2006 10:21 pm |
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| E=mc squared, smiley-face. An extremely large amount of energy can become an extremely small amount of mass, and vice versa. |
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| smiley_face
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| 124899. Fri Dec 08, 2006 3:06 am |
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| Yer, that's just the theory though. How the hell do you get your head around and actually understand a concept like?! |
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| dr.bob
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| 124911. Fri Dec 08, 2006 4:44 am |
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Energy and mass are the same thing just in different states.
A bit like water changing into ice and back again.
Except not.
Because changing state like that requires energy to be added or removed from the system. Changing energy into matter doesn't require any energy. Also, as Jenny said, it takes a whole lot of energy to make a little bit of matter, whereas it doesn't take loads of water to make a little bit of ice. |
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| smiley_face
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| 124913. Fri Dec 08, 2006 5:02 am |
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I think I sortof get it now. Still can't quite comprehend it properly, but I think I've understood how it works, if not the why.
Is there any reasoning behind the fact it's the speed of light squared? I'm assuming it's not just some fluke that it's the same number. According to New Scientist a couple of years ago, there's a possibility that the speed of light isn't constant, so what impact would this have? |
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| Gray
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| 124932. Fri Dec 08, 2006 6:17 am |
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The thing about relativistic and quantum physics is that you should on no account ever 'try to get your head around it'. It can't be done. All you can do is have an 'appreciation of' and 'familiarity with' the paradigms, but don't try to 'picture' things whatever you do. You'll go nuts.
Human intuition ends with Newton, pretty much - anything 'rock-sized'. Thereafter, the universe reveals how weird it is, and there's no reason to expect us to 'get' any of it in an intuitive sense.
| Quote: | | Is there any reasoning behind the fact it's the speed of light squared? |
There's some mathematical logic (see link below), if that's what you mean by 'reason'. But if you mean something like 'cosmically significant use of the number 2', then I can't help you.
http://www.btinternet.com/~j.doyle/SR/Emc2/Derive.htm
As with all things, you'll need to know quite a lot to be able to appreciate why this works... |
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| Davini994
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| 290703. Wed Mar 05, 2008 7:43 am |
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Interesting article on this in The Guardian I found today:
| The Guardian wrote: | In the late 1990s, astronomers noticed that light from very distant supernovae was dimmer than it should be, suggesting that some of these dying stars were far further away than theories predicted. The puzzle led to the hypothesis that the expansion of the universe was accelerating, and was being pushed along by an unknown form of energy, which they called dark energy.
The latest study suggests that space soot might be to blame, at least in part, for making distant stars appear more faint than expected. |
i.e. some people think that 'dark energy', and accelerating expansion of the universe might just be because there is more dust around than we thought, which effects measurements of distance of standard candles.
If nothing else this demostrates how difficult it is to come to any firm conclusions in astrophysics, due to the incredible difficulty in obtaining accurate measurements. |
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| Tas
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| 290776. Wed Mar 05, 2008 9:34 am |
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| Quote: | | Changing energy into matter doesn't require any energy. |
Eh? I thought that (for example) a nuclear reaction required the addition of energy (or external effect) to 'split' the atom. Or are we talking about theoretical happenings when one state becomes the other?
:-)
Tas |
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| smiley_face
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| 290946. Wed Mar 05, 2008 12:59 pm |
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| Tas wrote: | | Quote: | | Changing energy into matter doesn't require any energy. |
Eh? I thought that (for example) a nuclear reaction required the addition of energy (or external effect) to 'split' the atom. Or are we talking about theoretical happenings when one state becomes the other?
:-)
Tas |
Tas, Energy is never created or destroyed, it simply changes from one form to another. Mass is just another form of energy, like kinetic energy, gravitational potential energy, electrical energy, etc.
A nuclear fission reaction (which I presume is what you are talking about) requires an initial neutron. When that neutron is absorbed by a Uranium-235 atom, the Uranium-236 atom results. This is unstable, so the Uranium-236 breaks down to Krypton-92 and Barium-141. However, the total energy of the mass of the U-235 and the neutron is higher than that of the Kr-92 and Ba-141. This energy is converted into thermal energy, which is (leaping over a massive section of the process) how nuclear fission reactors are used to generate electricity. |
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| Davini994
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| 290961. Wed Mar 05, 2008 1:25 pm |
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| SF wrote: | | (leaping over a massive section of the process) |
i.e. an energy barrier, which is what you are talking about Tas. So you need to add a bit to get it over that, but you end up with the same energy (including the mass) back afterwards, including the bit you added to get over the barrier.
So for a chain reaction in a nuclear bomb, you add a bit, get some decay, then you end up with lots of energy converted from mass energy) and boom. |
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| smiley_face
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| 291102. Wed Mar 05, 2008 5:42 pm |
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Thanks for explaining that, Dav. I was running out the door to the gym (bloody training) while typing that message, so didn't get time to fully explain.
It's a bit weird for me reading the last 10 posts of this thread and seeing just how little I knew just over a year ago. |
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| Tas
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| 291141. Wed Mar 05, 2008 6:53 pm |
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So if energy and mass are the same (eg E=M), then:
E (Energy)= M (Mass) x C (S.O.L. in a vacuum) squared is misleading?
[/tongue in cheek]
My point was, mass does not change into energy without an external nudge of some sort.
:-)
Tas |
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| Davini994
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| 291246. Thu Mar 06, 2008 5:34 am |
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Well yes, E=M.
All c^2 is a conversion factor, it's a constant. If you use the right units of measurement then it's equal to 1. If you are dealing with physics that requires this conversion, or for astrophysics, you'll typically be working like this. |
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