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Energy is Matter is Energy? - confused layman here

  1. Jan 20, 2014 #1
    Hi, I'm new both to this forum and to physics in general. Here's hoping I've posted in the right place....

    I'm basically trying to understand the difference between energy and matter and how one can become the other. Please bear with me, I'm a total layman and can't seem to get a definitive answer anywhere online.

    So I guess I get the basics: Matter is made up of atoms which are made up of subatomic particles. But the added mass of the individual particles doesn't add up to the total mass of the atom. The remaining mass is made up of energy. The energy that was needed to bind the particles into a nucleus is converted into mass when the strong force takes over from the EM force.

    Which means that matter is partly converted energy.... But what about the particles that make up the atom? Were the protons, electrons and neutrons matter before they became bound together? Or were these particles themselves energy to begin with?

    The reason I'm confused is because free electrons are supposed to be electrical energy, not matter. And, seeing as photons are free moving and they are energy, I'm assuming that subatomic particles are energy until they are bound into an atom, making them matter.....?

    So essentially I'm asking, are protons, electrons and neutrons always matter, or can they be energy as well?

    Sorry if this is a dumb question. I'm certainly no physicist, just curious.
  2. jcsd
  3. Jan 20, 2014 #2


    Staff: Mentor

    Energy comes in a number of forms - thermal energy, potential energy, kinetic energy and others as well. Mass is a form of energy - but energy is not mass.

    Exactly what energy is, is slightly tricky. Its actually what's defined by this theorem called Noether's Theorem:

    What the theorem says is if something very fundamental and important to physics, called the Lagrangian, doesn't change when you do something to it like change your coordinates, then a conserved quantity exists. It turns out kinetic and potential energy are the invariant quantities associated with time invariance. Because of this nifty fact nowadays we define energy this way, and lo and behold it turns out mass is a form of energy.

    So basically because energy is what this nifty theorem says it is, mass is a form of energy.

    If you want to pursue this further, the book to get is Lenny Suskinds book:

    It also has associated video lectures:

    Last edited: Jan 20, 2014
  4. Jan 20, 2014 #3

    Not a dumb question at all. The way you worded it I believe all answers will be somewhat incorrect as some of the particles you listed are composite but mass is conserved and some of the fundamental particles comprise the electromagnetic fields that span space-time and are even more difficult to define. Let's hear the better informed posters as I am also not a physicist.
  5. Jan 20, 2014 #4

    Sorry, I must be the least mathematical person on the planet. Is there a way of simplifying the definition of energy in a non-technical way?
  6. Jan 20, 2014 #5
    Physics has got to be the most mind-blowingly difficult thing to get your head around. I guess I don't really understand what energy is. My brain just wants to be able to simply classify particles as either energy or matter...
  7. Jan 20, 2014 #6


    User Avatar

    Staff: Mentor

    Energy is a property of something, not a "something" in itself.

    For a sort of analogy, consider the color blue. Something can be blue, but you can't have just "blue" all by itself.
  8. Jan 20, 2014 #7


    Staff: Mentor

    Damn - found out - drats.

    You have run into a fundamental problem with physics - at some point the jig is up - you simply can't explain some things without math. Unfortunately this is one of them.

    Simply accept under the modern definition of energy mass is a form of energy. Energy can be transformed into one form or another - but can't be destroyed ie is conserved. One can convert mass into say kinetic energy (eg when uranium atoms split they fly apart but the mass of what they split into is a bit less - it has been converted to kinetic energy) and the energy in photons into mass (for example you bang two photons together, which have no mass, and you can get an electron and a positron out - which have mass) and things like that.

    Jtlbell is correct - energy is simply a property things have that is conserved. If mass suddenly appears something else with this property energy disappears and conversely.

    Last edited: Jan 20, 2014
  9. Jan 20, 2014 #8
    Math is not physics

    Physics use math, to create models which allow to predict behavior of natural phenomena.
    But math does not carry an explanation itself. There are numerous examples when using a math model we end up in trouble e.g. some solutions to Schroedringer equation lead to infinity etc.
    If we don't have a good, imaginable process and we base all our understanding on math we are using - this is not good physics.
    It is like predicting a strange, elongated star when looking through a telescope with a scratch and being sure it is there, becase telescope shows so.
    Physics describes reality, math is a model - less or more useful, but just a model.

    But coming back to your question No-name:
    Answer is difficult, because we still don't know what makes particles massive. We don't have a good explanation to this yet. Esistance of Higgs boson carries some answers, but not all.
    So, while we may enjoy using our smartphones and electronics, we as civilization still don't know this very basic thing - what is mass? Go for it, you may find an answer. Look at the math, but don't get overwhelmed by it. Math is not reality.

    More to your question No-name:
    Were the protons, electrons and neutrons matter before they became bound together? Or were these particles themselves energy to begin with?
    As said before, energy is just a parameter, so a particle cannot be its own parameter. However, electron and positron can come to life just from a single high energy photon of X-ray, right in the middle of vacuum. So in a sense, they come from pure electromagnetic energy of a photon, which vanishes the same moment.

    You probably could imagine a whole proton or neutron come to life in a similar manner, but we are unable to produce such a ultra high energy photon - the only way to produce e.g. protons (or other hadrons) for us a civilization is to create it through a set of collisions of smaller particles. If we can prove that those smaller particles come to life from a single photon, than not directly, we can prove that a proton could come from a single flash of electromagnetic energy.

    I hope this lengthy answer sheds some light on what caught your attention.
    Last edited: Jan 20, 2014
  10. Jan 20, 2014 #9


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    Science Advisor
    Gold Member

    Energy depends on frame of reference, e.g. in Newtonian physics transaltional kinetic energy is (mv^2)/2, but the value of 'v' and hence kinetic energy depends on the frame of reference. Mass doesn't depend on frame of reference and if you like the mass of a system is precisely the energy of the system that can't be transformed away by a change of frame of reference.
  11. Jan 20, 2014 #10
    This is a great mathematical explanation, but no offence - it says nothing about physical world. You just explained what comes from equations.
  12. Jan 20, 2014 #11


    Staff: Mentor

    The equations describe the physical world. That is why we perform experiments, to make sure that we are using equations that do, in fact, describe the world.

    If you think that they do not say anything about the physical world then you must not know how to speak the single best language we have for describing the physical world.
  13. Jan 20, 2014 #12


    Staff: Mentor

    I want to echo jtbell's answer on this. Energy isn't a thing that something can be, it is a property that something can have. Protons, electrons, and neutrons are matter and they have energy. An electron and a positron (antimatter electron) are matter and have energy, and if they meet then they annihilate each other and produce some photons which also have energy.
  14. Jan 20, 2014 #13
    Matter is a concentrated form of energy. Think of what happens when you split an atom causing an atomic explosion or bomb. You are converting matter (atoms) into energy.
  15. Jan 25, 2014 #14
    I think I get it a bit better now. I'm gonna watch a documentary on this subject tonight and hopefully it will cement my understanding.

    I find physics fascinating but have very little comprehension of maths, so it's interesting to read the almost philosophical mini debate here about the relationship between maths and physics.

    I'm gonna stay curious. Thanks for your help!
  16. Jan 25, 2014 #15


    Staff: Mentor

    I think the many professions that use math for its explanatory and predictive power from engineering to actuarial science would disagree.

    Even good old Euclidean geometry which explains the many properties of points and lines says otherwise.

    And when that happens it indicates something is wrong with our explanations and people look to fixing it up like Wilson did with the infinities that plague QFT - he got a Nobel prize for it. Rather than indicating there is any problem with using math, it shows it is the correct tool.

    I think you are a bit confused about what physical theories are - they are almost (but not quite) by definition mathematical models like a lot of other areas such as actuaries use. It's got nothing to do with what you think is 'a good, imaginable process' - its got to do with correspondence with experiment. And that's why actuaries use them as well, and why they get paid the rather large sums they do for their advice - it works. If you have a different approach that is better at that by all means have it published and you will change the face of science.

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