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Graviton energy and frequency/wavelength?

  1. Jun 26, 2008 #1
    Hopefully I can get some knowledgable help on this question. I'm not a physicist but I am an electrical engineer (by education anyway) and a database architect by avocation. I'm a bit of a physics junkie and some of my self study leads to this problem.

    I see a lot of mention of searching for gravity waves. I guess one of the sources would be massive binary stars (neutron stars or pulsars I suppose). These would cause ripples in spacetime. OK. So people look for gravity waves with the frequency of the stars' rotational period. BUT, to me that is not the frequency of the graviton but rather, it's an amplitude modulation of the gravity field. It would be like amplitude modulation in radio communications where you have an underlying carrier wave at a particular frequency and then you superimpose a lower frequency signal on top of it.

    In this case, the frequency of the photons involved would be that of the carrier wave. So this leads me to wonder, what is the frequency (or wavelength) of a graviton? If the energy of a photon is h nu and the photon is a massless particle like the graviton then wouldn't a graviton also have an energy equal to its h nu?

    I mean, if it's a particle then quantum mechanics dictates that it has a probability wave and ergo a wavelength and frequency. So is a graviton able to have a variable wavelength and if so, is there such a thing as an energetic graviton? Everything that discusses gravity seems to indicate that it is a fixed force dependent on mass. This seems to imply that the graviton (if it exists) somehow exists at only one wavelength but that doesn't make any sense to me. So what would be the effect of having gravitons of different wavelengths? Has anybody ever asked that question?
  2. jcsd
  3. Jun 26, 2008 #2


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    Gravitons can have any frequency, just like photons can. Gravitons are to the gravitational field as photons are to the electromagnetic field and can be generated in much the same way. If you cause an electric charge (such as an electron) to oscillate back and forth, it will produce electromagnetic waves (photons) at the frequency of the oscillation. Likewise, if you cause a mass to oscillate, it will produce gravity waves (gravitons) at the frequency of the oscillation. This is why you look for gravitons at the frequency of the binary spin rate. This is the frequency that the gravitons produced will be.
  4. Jun 26, 2008 #3
    Well, I have to question that response Janus. The gravitational field will be there regardless of whether or not it's oscillating. That means that gravitons are being exchanged in a stable environment and it's the wavelength of THOSE gravitons that I'm asking about. The binary pulsar rotation will superimpose an amplitude modulation on top of this gravitational field.

    So once again, I'm still wondering about the gravitons in a gravitational field.
  5. Jun 26, 2008 #4


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    The gravitational field is mediated by the exchange of virtual gravitons, which aren't the same as the actual gravitons that are the quanta of gravitational radiation (Gravity waves) which transmits information about changes in the gravitational field. (For one, they are not directly detectable). Again, the same is true with the electromagnetic field. The field is mediated by virtual photons and actual photons are the quanta of electromagnetic radiation (radio waves, light waves, etc.).

    When we look for gravity waves, we are looking for this gravitational radiation,
  6. Jun 26, 2008 #5
    As Janus said, the graviton/gravitational field duality parallels that of the photon/electromagnetic field duality. As an EE, does a stationary charge and its associated EM field bother you? This EM field is actually due to the exchange of virtual photons. Time-variance to that field (i.e. an EM wave) quantum mechanically realized as detectable photons.

    If you consider the Earth-Sun system quantum mechanically, you would find that a transition from its normal state to the next lowest state releases energy (graviton?) with a wavelength of precisely one lightyear (not a coincidence, I'll leave you time to think about it). This of course assumes the Planck relation holds for gravitons (which you did ask). I am not sure about the validity of this assumption, but it serves to illustrate a point: gravity waves/gravitons are difficult to detect because of such low energies/large wavelengths. That is why the proposals are to detect them as they result from black holes and other such large scale phenomena.

    EDIT: Sorry to repeat you Janus, we posted at the same time... =P
    Last edited: Jun 26, 2008
  7. Jun 26, 2008 #6
    cmos and Janus,

    Thank you for taking the time to give me thoughtful responses. You both did say something that confused me. You used the term "electromagnetic field". I've seen other people use that term. But I don't know what that is. I understand an electric field and a magnetic field and I understand eletromagnetic radiation but I don't understand calling that a field. But this is something that I'm very fuzzy on.

    Are you saying that electric and magnetic fields are mediated by virtual photons and em radiation is actual photons? I'm thinking about this ... I'm thinking about a static electric field. If it's not varying, then its frequency is zero. Well that seems to track with what you're saying. I guess then virtual photons are ones with a frequency of zero which gives them an energy of zero by E = h nu. So the existence of the field does not radiate energy if it's static. If it fluctuates, then nu > 0 and energy radiation takes place. Ok if all that is true then I have my answer. Gravitons mediating a gravity field do have a specific frequency, i.e. zero. Energetic gravitons are ones that are emitted by a varying gravity field. Now all I have to do is understand the math that goes along with that. But this is a start.

    About the earth moving to the next lowest quantum state, since the earth is very massive that quantum jump would presumably be very small? At any rate I suppose the jump would take one orbital rotation to complete, i.e. one year? The graviton travels at light speed, hence a one lightyear wavelength?
  8. Jun 27, 2008 #7


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    The virtual gravitons of the gravitational field vary in frequency/wavelength, thye just exist for limited for a limited time based on their wavelength. This by virtue of the uncertainty principle. Just like there is a relationship between the uncertainty of position and momentum for a particle, there is a relationship between the uncertainty of time and energy. The uncertainity of a virtual graviton's energy (and therefore wavelength) is inversely proportional to the length of time the measurement of its energy is made in.

    So a virtual graviton can come into existance with a given energy/wavelength, exist for a short time and then disappear as long as it exists for a short enough time. The greater the energy, the shorter the time. Any longer, and they would violate the law of energy conservation. Thus the gravitational field consists of virtual gravitons popping in and out of existance, the lifetime of any given virtual graviton being inversely proportional to its energy.

    When these virtual gravitons are exchanged between objects, it manifests itself as the gravitational force. The force exerted depends on the energy of the exchanged virtual graviton, and the virtual graviton must have existed long enough to traverse the distance between the two objects at the speed of light. Thus the further apart the objects are, the lower the energy of the exchanged virtual graviton and the smaller the imparted force.
  9. Jun 27, 2008 #8
    How does gravity exert its effects in a black hole? Can gravity waves radiate from the black hole?

    Are virtual gravitrons created outside of the event horizon?
  10. Jun 27, 2008 #9
    I would wonder if there is a graviton analogue to Hawking radiation; however, let's forget about that. Think about a charged particle moving in uniform circular motion. Due to the movement, there will be time-variance in the electromagnetic field (i.e. an electromagnetic wave or photons). Now replace "charged particle" with "black hole," "electromagnetic" with "gravitational," and "photon" with "graviton."
  11. Jun 27, 2008 #10
    There are several ways of looking at it.
    1) From Faraday's law and the Ampere-Maxwell law we know that time-variance in the fields induce each other. Thus we get that light is EM radiation. Then it is just convenient to talk about an electromagnetic field as opposed to saying electric and magnetic fields.
    2) From special relativity, observers in different frames of reference may observe different physical occurrences. Without going into the mathematics, what appears as an electric field to one observer may appear to be a magnetic field to another observer. So in reality, they must be one and the same; hence the electromagnetic field. In fact, in tensorial form (the language of relativity), Maxwell's equations reduce to two equations as opposed to the four that are present in vectorial form.
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