Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Photon's Mass?

  1. Nov 27, 2003 #1
    A photon isn't supposed to have mass. But yet it is effected by gravity. So this means that a photon must have the gravitational property. And this would give it mass. So why does gravity bend the curve of a photon? And please give me more than "gravity bends the spavetime continuum, so it effect the curve of the photon". Cause as I see that, bending in spacetime in towards a massive object would push the photon away. Cause there would be more "preasure", if you will, closer to the massive object, therefore pushing the photon away. And in that case, wouldn't you age slower on a still massive object then you would being still in space?
  2. jcsd
  3. Nov 27, 2003 #2
    But in general relativity, that's the correct answer.

    Why? It doesn't push away other objects, like electrons or planets. Why should it push away photons?

    I don't know what you're talking about. Spacetime curvature isn't pressure.

    Yes, clocks run slower on the surface of a massive body than they do far away from the body.
  4. Nov 27, 2003 #3
    Then spacetime would have to be a force, like a wave or something? Because unphysical things wouldn't be able to affect something that is physical. Like how could your imaginary friend kill your other friend. But then an object that does not have that wave type cannot be affect by the wave. So then the photon would have to have the gravitational wave type so it could be affected by spacetime. And this would give it mass.
    And gravity would seem to have a physical property making it a wave type(aether), thus it would affect space. And because it affects space it in turn affects time. So time would be a wave. And the two would work together to make "spacetime" which allows us to travel through this three dimensional space. Cause with only time you're everywhere, and with only space you're nowhere. So the two together give us what we are living in right now.

    sorry, long day.
  5. Nov 27, 2003 #4
    I had to reread the above before I saw that it made no sense. So I edited it. Please reread if you haven't already.
  6. Nov 27, 2003 #5
    Spacetime isn't a force, or a wave. Spacetime affects things physically because it determines their geometry. (Changes in the geometry can propagate as waves, though.)

    The rest of what you said didn't make much sense to me, even after your editing.
  7. Nov 27, 2003 #6
    spacetime itself is not real because time is not real so why dont you all be quiet about space time. Oh and the whole photon mass thing is not ecxactly untrue but things with no mass are stiil affected by mass so a photons curve is nnot unnusual at all given that time does not exist.
  8. Nov 27, 2003 #7
    Ok, so spacetime isn't a force or a wave. Then it can't directly affect physical objects. "How can your imaginary best friend kill your physical best friend?" I can't think hard then affect which way my car is going to go, so how can something that doesn't exist in reality even have a number in a mathmatical equation. My physics teacher tried to tell me that "that's just the way it works". Sorry man, won't take that. Only the physical can affect the physical. So if spacetime has no physical properties then how can it affect physical things. Like pulling in a photon. If the photon has no mass, then it has no gravity. Therefore it won't be pulled in to a planet by gravity, but how can it follow the curvature of spacetime if spacetime is only an imaginary thing.

    You said "(Changes in the geometry can propagate as waves, though.)" But that is after the fact. After a tragectory has been changed it will propagate a wave, but what got it to change course in the first place.

    And the sum of everything else that I said was, space and time are two different wave types working together to give us three dimensional space, or spacetime. The fourth dimesion is an illusion of the resulting effect.
  9. Nov 27, 2003 #8
    actually you could move your car with your mind and destroy it and recostruct it into anything even solid gold STUDY QUANTUM PHYSICS!
  10. Nov 27, 2003 #9
    Photosynthetic Absorbtion

    Solar photons can add Mass indirectly to plants through photosynthesis. I know this does not endow a photon with Mass, however it does ADD Mass to a plant.
  11. Nov 27, 2003 #10
    really though the mass added is from the water not the solar photons they just change the mass.
  12. Nov 28, 2003 #11
  13. Nov 28, 2003 #12


    User Avatar
    Gold Member

    spacetime itself is not real because time is not real so why dont you all be quiet about space time. Oh and the whole photon mass thing is not ecxactly untrue but things with no mass are stiil affected by mass so a photons curve is nnot unnusual at all given that time does not exist.
    who was it that said "fools rush in where angeles
    fear to tread"?
    i struggle with nonintuitive theories all the time
    but the bottom line is, unless one has a better
    theory its all we have, many many people have dedicated
    their lives trying to bring about a better understanding
    of science, and many more have learnt the theories
    that these have people have formulated, so if you
    want to ignore this wealth of information it is up to
    you, maybe some of you could formulate your own
    theories and re write science, when you have a theory
    share it with us and we can kick it around and see
    if it holds water.
    Last edited: Nov 28, 2003
  14. Nov 28, 2003 #13
    Of course this is not true. There is no law of physics that says that something has to be either a force or a wave to affect physical objects.

    Who said that spacetime geometry or spacetime curvature doesn't exist in reality? We can measure it, after all.

    As I have already said, spacetime has physical properties, namely, geometry.

    The trajectory of an object under the influence of no external forces depends only on its initial position and velocity, and not on its mass. That's Newton's first law of motion. In general relativity, the geometry of spacetime determines what a "straight line" is, so it determines the trajectories of all bodies, regardless of whether they have mass.

    If you're talking about a gravitational trajectory, it doesn't change course. It travels straight (but in a curved spacetime).

    That may have something to do with some theory you've invented, but it has nothing to do with relativity. You should post it to the Theory Development forum.
  15. Nov 28, 2003 #14
    Sniper___1, I have studied quantum mechanics, and like Einstein I have decided that there cannot be chaos in the universe. There only seems to be chaos because our puny brains can't handle everything yet. Though this always interferes with the positivist point of view that I try to hold. But in this case it becomes religous.
    Placks problem with trying to measure the speed and the possition at once was he was trying to do it on a three dimentional level. Though time adds a fourth dimesion, so the fourth dimesion could be graphed on a different three dimensional chart, put the two together and I believe that the uncertianty principle could be taken away.

    Ambitwistor, that thing at the very end was the start of a new theory I'm developing. And yes I will post it in the Theory Development when it's done. BUT, I have to bring up some aspects of it so I may prove my point.
    You said "There is no law of physics that says that something has to be either a force or a wave to affect physical objects." Never mind about the wave thing, but all "forces" exert physical activity, thus giving it physical properties. And later you said that we can measure the curvature of spacetime, so doen't that mean spacetime has physical properties. You said that "geometery" was a physical property. Please explain that, I don't rightly understand.
    More clearly what I was trying to say with the mass gravity thing was that gravity is the only force that bends spacetime, and the bending of spacetime affects only objects with mass. But to have mass you also have to have the gravitational property. So what I'm saying is for a photon to travel with the curvature of spacetime it has to work on it's level, so it would have to have the gravitational wave, which would give it mass. I figure that the mass of the photon can be calculated off the amount it curves around a massive object if the mass of the object is known and how far away the photon is.
  16. Nov 28, 2003 #15
    Yes, but forces aren't the only things that exert a physical influence.

    Yes; that's my point. Einstein couldn't very well have developed a theory of gravity based on the properties of spacetime if those properties weren't physical.

    Well, for example, just take a string and use it to measure the ratio of the circumference of a circle to its diameter. The geometry of space determines what that ratio will be; it doesn't have to be π.

    No, the geometry of spacetime affects everything, mass or not, because everything exists within spacetime.

    (And, strictly speaking, gravity is not a "force"; sometimes people call it an "interaction" when they want to be precise.)

    Gravitational waves are not needed for a body to exert a gravitational influence upon another, nor do gravitational waves give bodies mass.

    The mass of the photon has been measured and is known to be zero, to within experimental error. But even if it wasn't known, you could not use the experiment you propose to determine its mass, because the trajectory of a test particle in a gravitational field is independent of that particle's mass: Galileo determined that as an essential property of the gravitational interaction, and Einstein built it into his theory too in the form of the equivalence principle.
  17. Nov 28, 2003 #16
    Then you're saying that gravity directly effects the electromagnetic bubble (sorry, can't think of the right word) around the earth. As I've seen gravity can effect the particle in spacetime thus effecting the electromagnatism it produces, but never be able to effect the electromagnetic effect the particle produces directly.

    Scientists say that electormagnatism travels at the speed of light (this is where I always get confused) but then you have the effects created by those electormagnetic waves.
    So the path of the electromagnetic wave is c, then wouldn't the curvature of the electromagnetic wave be greater then c? And how fast does the electromagnetic effects travel through space?
  18. Nov 28, 2003 #17
    Do you mean the Earth's electromagnetic field? Yes, it does, but not by very much. But the influence of the Earth's gravity upon electromagnetic waves has been measured.

    Curvature is not measured in units of speed, so I don't know what it means to speak of the speed of curvature. Electromagnetic effects travel through space at c, as measured by a local inertial observer.
  19. Nov 28, 2003 #18
    I don't know enough about electromagnetic fields to argue my point well enough. Would you know of any reading material that I can use?

    So they say that electromagnatism travels out like particles, but behaves like waves. This is where we get particle-wave duality. When you see a picture of a electromagnetic wave it shows the wave traveling up and down, and at 90 degree angles to it. But do those waves "emit" more waves that effect other things? Like a fish swimming though the ocean. The fish is the origin of the wave, but then waves are created from that and travel even further. And if that is, what is the speed of those waves?
  20. Nov 28, 2003 #19
  21. Nov 28, 2003 #20
    What would you like to know? How gravity influences them? If so, you'd probably want to begin with the Pound-Rebka-Snyder Harvard clock tower experiment, and the gravitational deflection of light by the Sun. You can find discussions of those effects all over the place, including in any general relativity textbook. Ohanian and Ruffini is a good choice for this, and you can read summaries in Cliff Will's book or his online Living Review on experimental tests of GR. Treatments of them usually work within the semi-classical approximation of considering massless classical test particles, but you can find geometric optics approximations and such in more advanced texts like Misner et al. For a discussion of full Maxwellian electromagnetism in curved spacetime (the Einstein-Maxwell equations), you'd also want to look in an advanced GR text, such as Misner et al, Wald, etc.


    In this analogy, the "fish" is a charged particle, and the water waves that are produced by its motion are the electromagnetic waves.

    Electromagnetic waves travel at the speed of light. Electromagnetic waves are light.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook