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Mass and Energy

  1. Jul 14, 2006 #1
    Hi all,

    Matter can be turned into energy, correct?

    If so, what happens to matter's gravity when it's converted to energy?

    Also how fast is gravity? If the sun was hypothetically removed, would the Earth cease falling towards the sun's former position immediately, or in ~8mins?

    Thanks
     
  2. jcsd
  3. Jul 14, 2006 #2

    Danger

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    Hi, Nahaz. Welcome to PF. I'm not certain about your first question. Energy can have a mass-equivalence with regard to gravity, as far as I know. A high enough energy density, for example, can form a wormhole. (A negative energy concentration is needed to sustain it.) Long story short... I'll leave this for someone else more qualified.
    According to both theory and all observations to date, gravity travels at the speed of light. Your removal of the sun, therefore, would be noticed gravitationally at the same time as it would be visually. That, as you indicated, is approximately 8 1/2 minutes after the fact.
     
    Last edited: Jul 14, 2006
  4. Jul 14, 2006 #3

    Kurdt

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    Matter when converted to energy forms E.M radiation. The radiation can be affected by gravity but has no gravitational influence of its own as this requires mass.
     
  5. Jul 14, 2006 #4
    In fact, EM radiation does act as a source of gravity. Anything with energy (or momentum) does. This, however, is only manifest in the source term of General Relativity, not in Newtonian gravity.
     
  6. Jul 14, 2006 #5
    Am i wrong or you said 2 different things? Parlyne says that em causes a grav field and Kurdt that it doesn't.

    However energy is only EM? couldn't matter become another type of energy...i don't know...not EM?
     
  7. Jul 14, 2006 #6

    Danger

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    Matter can, of course, become other types of energy, if you use a looser definition. Electrons, for example, are considered beta radiation when they start running amok. Likewise for alpha radiation, which is essentially a hydrogen nucleus (proton, or proton + 1 or 2 neutrons), and neutrons themselves are considered radiation in a bomb or reactor.
    On the bottom level, matter is just energy in a bound state. By that token, all matter is already energy. That, though, is EM when fully broken down. Matter + anti-matter = gamma.
     
  8. Jul 14, 2006 #7

    Kurdt

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    Well while it is true that photons have self gravity I thought it best not to get into the details of considerenig the nature of the self gravitation for photons. But consider the fact that a photon travels at the speed of light and so does the gravitational force.
     
  9. Jul 14, 2006 #8

    Danger

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    Yeah... it's a pretty squirrelly subject. In fact, it's quite beyond my educational level. I was just kind of summing things up with the least hassle (to me). :biggrin:
     
  10. Jul 15, 2006 #9
    It is more correct to say that matter can be turned into EM radiation and that for the mass, m, of a closed system there is a total energy, E, which corresponds to this mass. E.g. increase the energy of an object and the object's mass will increase. However both the total energy and the total mass of any closed system is a constant which cannot be increased nor decreased.

    Pete
     
  11. Jul 16, 2006 #10
    This, to me, makes the most sense about mass-energy conversions. It is easy to think about, and there is no possibility that it can be faulted.
     
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