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What is energy in reality, is it PHOTON?

  1. Mar 11, 2012 #1
    What is energy in reality, is it PHOTON??

    When mass is annihilated, two photons or light is produced. That light has very high(or highest) energy level. As the energy of light depends on it's frequency and wavelength it means that photons are not energy themselves but just energy carrier(guage boson for electromagnetic force). Now the question automatically arises that if it is just about not being mass that even a graviton or gluon does not have mass but are energy carriers but they are not produced as energy. what is energy in reality then. I don't think the classical definition are right:"The ability to do anything"
    There must be some REAL form of energy than kinetic, potential or others. It is even said that energy can bend the river of time(i mean to say time out of the space-time fabric) and it is also discovered that high energy can from one side grow and from other side shrink the spacetime fabric, making faster-than-light travel possible. Than what is PHYISICAL existence of energy
    And last thing, why two high energy photons can not produce mass?
  2. jcsd
  3. Mar 11, 2012 #2
    Re: What is energy in reality, is it PHOTON??

    I don't see how that logically follows in any way. It is true that photons are the gauge boson of the electromagnetic force, but that doesn't imply anything else you said.
    It's really hard to define energy, either you define it in a vague way (like the ability to do work), or you define it like E=Mc2, which is sort of recursive. Instead of thinking of energy as a thing, think of it as a quantity, i.e., every particle has a certain amount of energy. Consider this analogy: Nothing is pure energy, just like nothing is pure color. Things can have color, and things can have energy, but color cannot exist without something to be colored, and the same goes for energy.

    I'm not sure what you mean by this sentence, but even if I did it's wrong. Nothing travels faster than light, where did you hear this?

    I don't understand the question.
  4. Mar 11, 2012 #3
    Re: What is energy in reality, is it PHOTON??

    You left out the Z0, W+ and W- bosons, the carriers of the Weak Force. But, they have mass.
  5. Mar 12, 2012 #4
    Re: What is energy in reality, is it PHOTON??

    I think he's trying to talk about the Alcubierre drive.

    I think he's wondering, "well, an electron + a positron turns into two photons (gamma), so why can't gamma + gamma become, e.g. an electron and positron, which are massive?"
  6. Mar 12, 2012 #5
    Re: What is energy in reality, is it PHOTON??

    I got everything. Thanks for help. Actually it is this video which made me confuse about FTL travel and made me think of pure energy. please explain it to me.
  7. Mar 12, 2012 #6
    Re: What is energy in reality, is it PHOTON??

    You got it. Exactly I wanted to say it. I was so confused that I could not find words for asking. please tell me why two gamma + gamma create mass(electron and positron)
  8. Mar 12, 2012 #7

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    Re: What is energy in reality, is it PHOTON??

    Saying that two photons can't produce massive particles is tantamount to saying that time is not reversible at the quantum level. This would constitute a CPT violation.

    A pair of high energy photons can collide and create a particle/antiparticle pair. It's called pair production. Even a single high energy photon can result in pair production in the vicinity of a massive particle, which is needed to conserve momentum. A pair of high energy photons can result in pair production in the absence of a massive particle. That's what happened shortly after the big bang. The cross section for photon-photon pair production is rather low, but it is not zero.
  9. Mar 13, 2012 #8
    Re: What is energy in reality, is it PHOTON??

    Energy is a very enigmatic thing. In the title you ask if energy is a photon. Here is an example of when it might not be. Say we have an object low down in a gravitational well. When we raise the object its potential energy increases. Where is this additional energy stored? In Newtonian theory, it is said to be stored in the gravitational field but things are not so clear in General Relativity that does not even require (or so I am told on this forum) that energy is conserved. Either way, gravitational potential almost certainly does not exist in the form of photons and may be nothing more than a book keeping exercise. Now let us look at kinetic energy. Let us say we have a cricket ball travelling past us and heading towards a window. We say the ball has kinetic energy and this seems to be a tangible quantity especially when it arrives at the window and smashes it. It certainly meets the definition that energy is the ability to do something. However, if we switch to the rest frame of the cricket ball the kinetic energy disappears and now it the window (and the house and the Earth) that has the kinetic energy. If we conjecture that energy is in reality made of photons, are those photons attached to the ball or the window? Whatever tangible form we give to energy becomes undefinable in an absolute form because kinetic energy is observer dependent. Things become even more bizarre when we consider Unruh radiation. An accelerating observer sees energy and even particles radiating from an apparent event horizon while an inertial observer in the same location does not observe the radiation. In this case we have particles that are observer dependent in that they exist for one observer but not for another!

    Now let us look at the relation between matter and energy. One way we could define mass is "mass is energy that has an identifiable rest frame". By this definition a single photon does not have rest mass. On the other hand, two photons travelling in opposite directions do have a rest frame and therefore have rest mass and can act as a source of gravity. We can in principle have a black hole made up just of photons.

    Loosely speaking, yes it can, but so by the same token can mass. As mentioned above the line between mass and energy is very fine and mass may be nothing more than localised trapped energy.

    As others have mentioned, they can.
  10. Mar 13, 2012 #9
    Re: What is energy in reality, is it PHOTON??

    Why photons are produced when mass is annihilated? Why not gluon or why not other particle which carry energy. I guess if electron-positron(electromagnetic particles) annihilate they produce energy in form of electromagnetic energy(light). If, I guess, two particles which just have color charge no electric charge then gluon would be produced? Am I right?
  11. Mar 13, 2012 #10
    Re: What is energy in reality, is it PHOTON??

    Yuop has provided a number of examples contradicting what appears to be your hypothesis.

    Simple answer: no it is not.
    Another example close to one of Yuiops: gravitational wave [energy] is not photons. Nor are alpha, beta, but gamma rays will be.
    And heat [energy] transfer has little to do with 'photons'....especially convection, conduction, while radiation is related to photons.

    That is an incorrect assumption. Quantum mechanics, part of the Standard Model of particle physics, provides the rules which appear to govern the 'world of the small'.

  12. Mar 14, 2012 #11
    Re: What is energy in reality, is it PHOTON??

    thank you very much, I got it.
  13. Mar 14, 2012 #12
    Re: What is energy in reality, is it PHOTON??

    But I like the question :)

    What the he* is 'energy'?
  14. Mar 14, 2012 #13
    Re: What is energy in reality, is it PHOTON??

    What is bothering you about the various answers?
  15. Mar 14, 2012 #14
    Re: What is energy in reality, is it PHOTON??

    Nothing bothers me with the answers, but I'm really interested in what the 'concept' of 'energy' should be seen as. I find the concept widely used but I'm not sure how to see it. for example, 'fields' are a nice idea :) Could I think of 'energy' as a 'field', what kind of 'field' if so, relativistic or 'static', or both? Or should I consider it to 'transformations', expressions expressing themselves from interactions primary? A gravitational wave has both 'energy' and 'mass' theoretically. But I can also see it as a geometrical displacement 'propagating' in SpaceTime.

    So what is 'energy'? Is it 'something' by itself? Or more of a relativistic expression of transformations, or something else that I don't see at all? Someone recently suggested that one might see it as "an ability to create action." And I'm sure there are more descriptions than the ones I took up now possible.
  16. Jul 18, 2012 #15
    Re: What is energy in reality, is it PHOTON??

    What about the state of the universe a moment before the Big Bang (or Big Bounce)? Wasn't matter and energy all one and the same -- hence, pure energy?
  17. Jul 18, 2012 #16
    Re: What is energy in reality, is it PHOTON??

    It might have all been one big mush, but all the energy was contained in various particles interacting, even if only for a fraction of a second.
  18. Jul 18, 2012 #17
    There is no such thing as 'pure energy'. There is no scientific measurement of the 'purity' of energy.
  19. Jul 19, 2012 #18
    Re: What is energy in reality, is it PHOTON??

    pure energy means that the energy is not carried by matter, it is just energy. No Kinetic energy or electromagnetic energy which are forms of energy, but actual energy. Mass is made of energy, so the matter which does not have mass must be energy themselves as they are energy carriers for example photons and gluons. they might be just energy not EM or Kinetic energy which are forms of it.
  20. Jul 19, 2012 #19
    No such thing exists. There are a wide variety of forms of energy, but there is no such thing as floating blobs of energy, let alone whether or not it's 'pure'. Energy in special relativity is defined as [tex] E^{2} = p^{2}c^{2} + m^{2}c^{4} [/tex] As you can see, the right term drops out for massless particles. The left term is still there. The energy of the photons comes from it's (relativistic) momentum.
  21. Jul 19, 2012 #20
    Re: What is energy in reality, is it PHOTON??

    Energy is a property of bodies. There's no such thing as "pure energy" any more than there is such a thing as "pure color."

    "Pure color means that the color is not carried by matter, it is just color. No purple, or orange, which are kinds of color, but actual color."
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