So, the big question is… Explain: In physics and astrophysics, I was taught that matter/energy (specifically energy) is neither created nor destroyed. It merely changes from one form to another.
It’s been awhile since my college days and I feel like this is probably still the paradigm. However, I make mistakes like the rest of you. So, can anyone verify or dispute whether this statement is correct or not?
If so, please explain why or why not.
Thankyou, I’ll follow up later. 
Wow, what is it with a big ol’ heavy question like that in MPSIMS? Huh? You drop a bombshell like that in here and don’t expect to be called on it? Huh? 
Sounds like you got it about right. Mass and energy are always conserved. If you burn a log the mass of combustion products at the end will be the same as the mass of the log and the oxygen which was used to burn it up. You will have generated an identical amount of heat, light and sound energy as the potential (chemical) energy that was used up in the combustion process. There ends the log analogy.
Chronos explained some stuff to me a while back. When matter is converted into energy in the sun, the light energy produced weighs the same as the matter that was burned up. That is pretty cool. Light has mass. Sort of. He explained it better. The universe is a closed system and always has had the same mass. Pretty cool as well. Hope that helps, and I have not strayed too far into out and out wrong.
[QUOT=InvidiousCourgette]Wow, what is it with a big ol’ heavy question like that in MPSIMS?
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It’s because where I’m headed with this. I want to get a consensus on the theory/fact/law of physics before I take it to the second level, whib=ch WILL bring it here.
AND
From my experience, any other forum is gonna take me into the pit where I’m gonna have to deal with all kinds of bullshit
I suppose I could’ve started the thread in GQ…then started another thread in IMHO…then went to ???
So, I assume that so far nobody disputes the fact that matter is “eternal”?
as far as the time/existence of the universe is concerned?
damn my coding sucks :smack: I’ll redo that if need be. jeeze
IANAPhysicist.
Matter CAN be destroyed, as described in E=mc2 (squared). You get a truckload of energy per milligram of matter destroyed. I’ve been trying to find out how much matter was destroyed in the Hiroshima atom bomb, but it wasn’t much.
Teachers tell kids that matter can’t be destroyed because otherwise the kids (like me, previously) count the mass of an escaped gas as “destroyed matter.”
Even in a first year college chem class we calculated the mass lost in a chemical reaction. You just take the joules evolved and use the formula above, IIRC. It isn’t much at all, as you can imagine.
What it drove home is that basically ALL energy is created by destroying matter. Everything that’s ever been done on the earth got its energy in one way or another from a chemical reaction. Even things driven by the sunlight got their energy from the fact that a helium nucleus has less potential energy than two hydrogen nuclei. The escaped energy is where we get all that light from.
Cardinal You see the problem I have with this is that I wasn’t in a grade scool class. this was a 400 level astrophysics course and the prof said that all the matter found in the universe should be the same as it was in the beginning. That was the premise of my thesis based on Hawkings book about Dark matter.
While it is true that the measurable energy/mass appears to be reduced in nuclear reactions it is in fact being reconstructed into subatomic particles which have such a small amount of matter that we actually can’t measure it. It is like the weight of a photon. While the mass is minute…there is mass. Because there is energy (light) there must be mass. Therefore nothing was actually destroyed it was simply reduced to an “immeasurable” quantity.
Fission simply rearranges quantum particles due to extreme heat and pressure. But to claim that the SUN actually is creating matter would be a falsehood. For instance…what happens to the heat/energy when a sun “dies”. Does it simply cease to exist, or is it dispersed throughout th esolar system in which it originated in a very low “measurable” consistancy? (ie:background radiation)
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Well, I see the point that Enstein was also essentially saying that if there’s energy, even in light, there must be mass. But I’ve also been told that light has no rest mass. I don’t truly know what the implications are of that. I understand what you’re saying, though, I think. If we account for all the mass AND all the photons and temperature joules through the universe, we should get the starting mass of the universe.
I certainly didn’t mean that the sun is creating matter. That would require it to be sucking energy in enormous quantities from a source that I can’t begin to imagine would be available to it.
When a sun “dies”, I think it just stops created fusion. Note that stars are using fusion, not fission.
I don’t think I understand your question about what happens to the heat. Do you mean that you can’t think of a way for the heat to escape the star that is no longer sending out light rays due to fusion?
If I do understand you, then the answer is that (as I’ve been pounding into the heads of my 9th grade science students), warm things give off infrared light. The star will give off whatever frequency/energy photons it is capable of until all the energy is gone.
I think Einstein was saying that Mr. Spock was wrong. There is no such thing as “pure energy”.
astro I appreciate the input buddy, but if you don’t mind, would you clarify the point you’re trying to make? please
Cardinal I understand that as our sun is in its present state produces energy through FUSION, as I recall the creation of stars is by fission, the breaking down of atoms into their subatomic stat whereby pressure (gravity) and thus heat cause these atoms to combine (fusion) and give birth to the star in its current form.
Which does corroborate the idea that energy/matter is only transformed from one state to another. Not “created” from nothing and also NOT “vanishing” into nothing. That is at the most extreme level in which science can state is fact. Anything less, such as we would experience would be a given. (ie: boiling water, burning carbon, etc.)
The latter examples I assume most people would obviously agree that WE (mankind) are not capable of actually creating nor actually destroying anything completely, correct?
You are correct. You cannot create or destroy matter or energy completely. All you can do is rearrange it and shove it from place to place. In fact, matter can be thought of as nothing more than an exremely compact form of energy.
You-didn’t-ask-but-I’m-feeling-talkative: matter-energy conversions in decreasing order of energy output.
Matter-antimatter reactions convert the total mass of a system into radiant energy. Proton-antiprotion collisions in particle accelerators do this routinely.
Energy is released in fusion reactions when two light nuclei are slapped together. A tiny percentage of the mass of the fused nuclei is converted into energy. Energy is released in fission reactions when a large nucleus is split in two. Again, a tiny percentage of the mass of thnucleus is converted into energy. Anything lighter than iron can in principle be fused into heavier elements and relase energy in the process. Anything heavier than iron can in principle be fissioned to release energy. If you are unlucky enough to be iron, you’re stuck, at the bottom of the “binding energy curve”.
Exothermic chemical reactions involve shuffling around the electrons that orbit the nucleus, and release yet smaller quantities of energy.
But any way you look at it, the total mass/energy of the system is conserved.
But back to the question I quoted. While you cannot destroy the mass/energy of a system, you can destroy the order of that system (that is, increase its entropy greatly.) Say I have a planet. Say I don’t care for its inhabitants. I hurl an antiplanet at it and (somehow) arrange it so that every particle of the planet meets up with an antiparticle of the antiplanet. Boom! Lots and lots of radiation, no planet or antiplanet. A highly ordered system (with people, buildings, libraries, parks, grasslands, i.e. lots and lots of stored information) becomes a highly disordered system (a big mess of undifferentiated gamma rays.) So the argument can be made that while you have not destroyed the mass/energy of the system, you have destroyed the information content of the system.
Whew, I’m glad I got that off my chest.
Just as a caveat, IAAPhysicist. Just as another caveat, this is my first SD post. Oy, what a way to begin!
Conservation laws in physics really require a very specific definition of what it is that you’re conserving, and this seems like a language problem more than anything to me. You were once told that “matter is conserved” – which really depends on what the definition of “matter” is. If “matter” is the stuff that makes up protons, neutrons, and electrons (or collectively atoms, leading to the definition "Matter is something you can bump your head into :smack: ), then no, matter isn’t conserved. The statements above about nuclear reactions in the sun are a good example of this – matter is continuously being converted to energy (in the form of photons, non-head-bumpworthy stuff).
(Second caveat: light has momentum, which means it can push solar sails and stuff, but I still don’t think that follows people’s intuitive definition of what “matter” is.)
To me energy is a more general concept than matter. Matter is a subset of energy (you can think of it as “bound up” rest-mass energy, E=mc^2, with the potential to be liberated under the right circumstances), but “energy” covers both momentum (or kinetic energy), rest mass, and force relationships (e.g. potential energy, like gravitational potential energy). One of the deep fundamental rules of physics IS that energy (when counted among all these places) is conserved. There is no corresponding rule about “matter” in the common definition of matter.
Of course, there are other conservation rules, like lepton number, baryon number, etc etc… There are theories (like supersymmetry) that allow a bunch of these to be violated, but momentum and energy conservation laws aren’t rationally violated in any rational proposed theory that I’m aware of.
So the next time someone says “What’s the matter?”, you can mutter “Unconserved”.
Slight hijack:
This is a great book for laypersons who want to understand e=mc2. The author was inspired to write it after seeing an interview with Cameron Diaz in which she said she’d like to understand the equation. What makes it interesting is that he discusses all the prior scientific discoveries that Einstein basically tied together in the theory of relativity.
I really read the whole thread
Welcome to SDMB, hope you decide to join us…you’ve got a nice sig line already.
I was providng a cite and answer for cardinal’s question (quoted directly above my cite) looking for the approximate amount of matter annihilated in the 15 kiloton Hiroshima bomb explosion.
Thanks, Astro. I’d gone through a couple Google pages but not found anything. What search term did you use?
hiroshima gram matter
gotcha ya thanks
Okay, I think we’ve established the idea that energy doesn’t simply disappear. Energy is used and/or changed into another form or is dispersed into the atmosphere or maybe stored into matter as potential energy. In other words it still exists.
For example a battery is stored energy. It has the potential to move matter. It can be used for a multitude of things. When that battery is “used up” the energy it had stored is spent but still exists in the work that it performed. The battery may be recharged (maybe) by taking energy from another source and containing it in the cells of the battery. The alternator or generator that is used to do this is simply recycling a small amount back to the battery (in a vehicle for instance) and it gets stored again. But the battery could be charged by a completely different source as well.
Does that sound correct for the most part?
I just realized an error in the previous statement in that, the fuel in a vehicle IS the other source which when burned provides the energy. Some of which goes back into the battery.