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Is it possible?

  1. Jan 31, 2005 #1
    is it possible to make matter into energy and turn it back?
     
  2. jcsd
  3. Feb 1, 2005 #2
    Is it possible to make matter into "regular" energy? Yes. That's what basically happens during nuclear fission. Theoretically, you should be able to turn some of it back, but don't forget that good old thermodynamics says that you won't have as much as you started with: some of that energy became worthless heat.
     
  4. Feb 1, 2005 #3

    Chronos

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    Sure, they do it everyday in particle accelerators.
     
  5. Feb 15, 2005 #4
    Matter can be transformed into an energy as Chronos and Manchot said. Einstein's equations helps us to calculate it. And Daark Nova also asked that "How can we get back the energy as matter?" In accelerators, as a particle is accelatered, the energy given to it shows itself by increasing of the particle's mass because of the fact that any particle cannot reach the speed of light.
     
  6. Feb 15, 2005 #5
    Daark Nova,

    Perhaps it would be better if you thought of energy not as a thing but more of as an abstraction. Even though we quantify energy it truly is an abstraction of things that we can actually measure and count. For example, kinetic energy is an abstraction of the measure of mass and it's velocity squared. There are many kinds of energy but they are all fundamentally based on abstractions of the things we can measure directly. Here is the Wikipedia write up on energy that will give you more than I can at the moment.

    When considering the sub-atomic interactions that you seemed to be insinuating there are a lot of very detailed and interesting things that happen. For example, when an electron and positron collide, they will annihilate each other and give off gamma rays. Now even though the electron and positron have disappeared and been replaced by a gamma ray(photon), in terms of energy nothing has changed and everything has been accounted. This is where the conservation of energy is key to describing physical systems. Another interesting sub-atomic phenomena is describe by Feynman involves two, say, gamma ray photons interacting with each other. Though this is oversimplified, when two gamma ray photons 'collide' they create an electron and positron pair which destroy each other and then the two gamma ray photons go on as if nothing happened. Of course this is only allowed in very short time intervals and there is a lot more to it than what I can go into at the moment.
     
  7. Feb 16, 2005 #6

    That too but particles are created out of energy in an accelerator. Many particles only exist at extremely high energy densities. The whole point of colliding particles at such high velocities is that the particles form, produced just from the kinetic energy of the colliding particles, that is made from pure energy.
     
  8. Feb 16, 2005 #7
    franz,

    What exactly is 'pure energy'?
     
  9. Feb 17, 2005 #8

    YEha i guess i should be mroe careful with what i call things. When the particles collide, energy is released into the space around them, at high enough energy densities many previously unknown particles were found to form from the energy released. They weren't direct products of the collisions themselves, but formed out of the energy released itself, meaning if you added up all the rest masses of the particles you started with, and compared that to the total rest masses of the particles you ended with, the second would be higher. However this only happens at sufficiently high energy densities.
     
  10. Feb 17, 2005 #9
    Apparently your are missing the point of my post. Energy is an abstraction and to think of it as a 'thing' onto itself is misleading. We can talk about the the rest mass energy of an atom, the relativistic energy, energy levels, and on and on. But to catagorize energy onto itself as a thing will mislead us in our conceptualizations of what we are really talking about.

    I feel compelled to do this because I had made the same mistake at one time as well as just upon general principles. Go back and review the physics that you have studied and you will realize what I am trying to point out. Perhaps it might be more intuitive to say that we cannot 'observe' energy per se, but from our observations we can account for energy. It is subtle but important to point this out otherwise we will obfuscate the systems that we are talking about and begin to think that 'energy' is actually a thing. Not to mention the host of people who like to push crystal power energy and other absurdities! :rofl:
     
  11. Feb 18, 2005 #10
    No, thats really not true. Energy is an abstract concept in so far as it is intangible and badly taught, but it is a thing unto itself. The only question is what form it is in, i.e., how it is stored at a location. There is radiant energy, thermal energy, kinetic energy. Those forms of energy are very much real. Potential energy is a little bit more complicated, in that it is stored energy.

    Again, no, not really.

    No, i've been working on energy transport problems for a while now with one of the professors here.

    I will grant that i did not word my post very well the first time. As for the second time, my failing was that i do not know into what the form the energy is specifically released (not my field of physics). But the post still stands.

    Again, no thats not really right.

    For example i'm currently working on a computer simulation of energy transport within the sun, specifically interested in the convective layer, and how convection is at work in the sun, for example: If we change the energy flux at the bottom of the convective layer, how long does it take for the structure to reorganize itself in response? How are the convective cells structured? Layers? Columns? Does the path of flow expand horizontally as gas rises? How are is the direction of flow in one cell related to the direction of flow in another? What percentage of energy transport is actually done by convection in the convective layer, as opposed to the percent done by radiative transport?

    In all of this work treating energy as a 'thing' unto itself is very important. I have to deal with energy in put and one end, energy release through radiation at the surface, thermal energy transport through the convective mechanism itself, as well as readiative transport in the convective layer.

    This really would not be possible if i did not treat energy as a 'thing'.

    Energy is an intrinsic property of a physical system, like mass. Just as there is a mass density, there is an energy density. There is conservation of mass as there is conservation energy. There is a flow of mass into and out of a system, just as there is a flow of energy into and out of the system.

    Energy is just as much a 'thing' in of itself as mass is.
     
    Last edited: Feb 18, 2005
  12. Feb 18, 2005 #11
    Can one directly 'measure' energy?
     
  13. Feb 18, 2005 #12
    Can one 'directly' measure mass?

    No, you can only compare it to another known mass on a scale. Or calculate from known observables. Energy works the same way.
     
  14. Feb 19, 2005 #13
    Now you are confusing some things. The comparison is only needed to establish a basis by which you can measure things against. It is arbitrary and does not matter other than being consistent within that basis. The term 'observables' is from QM which has more to it than you are implying plus it is statistical, this will not be necessary for this discussion. Although it must be noted that one can often equate an 'observable' with a measurement. In QM energy is considered an 'observable' but that is based upon the measurements of the momentum and potential for the system in consideration. Of course it only gets crazier from there. When it comes to mass, I have found that the definition of it being the measure of an objects resistance to a change in momentum to be the most concise, at least in the classical sense.

    I think it is a good idea to consider that there are truly only a few things we can actually measure, everything else is an abstraction. For example, from thermodynamics, entropy. One cannot directly measure the entropy of a system but one can measure the temperature(ie the average microscopic molecular velocity), volume, number of molecules, and the pressure(force per unit area on the surface of the volume considered). Given these measurements we can calculate the entropy.

    So let's briefly examine the classical notion of energy. When we talk about the energy of a system we generally consider that to be the sum of the kinetic and potential energies which is assumed to be constant. Since the assumption is made this allows us to apply a variational method to the action integral that helps us prove that a particle will transverse a particular path instead of another one. But when you examine these 'energies' you find that the kinetic is based on the measure of the momentum and the potential which is based upon the measure of the distance from the source point in a field, as with gravity for instance. So there you have it, one does not measure directly the energy but bases the definition of it on things that we can actually measure.

    I'm making this point because Daark Nova had asked whether matter, a sub-atomic physics term, can be transformed into energy. Well it kind of is a ludicrous notion because of the lack of definition of the word 'energy'. One could very easily say that matter is energy and vice versa. But this seems to lead to a little more confusion because of a lack of properly contextualizing and defining the term 'energy'. As stated from your post, phrases like 'pure energy' begin to be thrown around and the next you know we'll being hanging out in So-Cal buying crystals, taking yoga instruction and starting a commune from some strange self proclaimed guru of the mysteries of 'pure energy'. :rofl: Finally, I am relaying a comment one of profs made one day while we were hanging around and chatting. He made the statement that energy was an abstraction and immediately it began to 'click' in my mind what he was saying. So this is how I pay that back. :biggrin:

    I dont think 'debating' these points with the intent of winning something will yeild either of us anything useful other than ego gratification and validation of our own self-delusions. It would be much more fruitful if we are to bring clarity to our personel understandings of these concepts and ideas so that we will be able to relay them coherently enough for it to be of use to those with which we share.
     
  15. Feb 19, 2005 #14

    learningphysics

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    Doesn't SR imply that potential energy is mass.... if we have a compressed spring, that decompresses pushing a cart on a frictionless surface... the cart bounces elastically off the opposite wall comes back, and recompresses the spring...

    Isn't the mass of the compressed spring greater than the mass of the decompressed spring by E/c^2, where E is the potential energy of the spring (and then later the kinetic energy of the cart).

    Isn't mass converted to energy and back here?
     
  16. Mar 1, 2005 #15

    SpaceTiger

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    That's my impression from this argument. Generally, I tend to see things from polyb's point of view, but it's really just a semantic/philophical point. Debating whether the real "thing" is energy, mass, matter, or radiation doesn't help us at all in our physical understanding.

    I sort of interpreted the original question more along the lines of "can you turn mass into radiation and vice versa"? The answer to that, as has been stated already, is yes. If the question really is about energy, then it probably doesn't make a whole lot of sense, since mass is a form of energy.
     
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