Questioning speed of light and infinite mass

  1. If Einstein's theories are correct, specifically about objects approaching the speed of light and their mass approaching infinity, how is it that a photon (and object with mass or mostly energy) is able to remain nearly massless? Why doesn't an electron fired through a particle accelerator approach near infinite mass and throw the Earth out of orbit? or worse? Are the equations wrong to presume that all matter at the speed of light reaches infinite mass? Why doesn't light also curve space?

    - An uneducated curiosity

    Last edited by a moderator: Nov 2, 2011
  2. jcsd
  3. Janus

    Janus 2,524
    Staff Emeritus
    Science Advisor
    Gold Member

    Photons have zero rest mass. Only objects with non-zero rest masses would have an increase in relativistic mass.
    Accelerating an electron up to 99.9999995% percent of the speed of light (about the highest accelerators have achieved) would increase its mass by a factor of ~100,000, since the rest mass of an electron is only 9 e_31 kg to begin with, you would only be increasing its mass to around that of an average atom.
    Secondly, the energy to accelerate the electron has to come from the Earth, and this would reduce the relativistic mass of the Earth. IOW, the Relativistic mass of the electron-Earth total would stay constant.
    It does, But the mass equivalence of light is quite small. The light put out by 1 billion 100w light bulbs in one year only has a mass equivalence of ~35 kg.
  4. Also, as a slight addition to the above, as an object increases in speed, it gains mass-energy or relativistic mass, the rest mass does not change, and it is rest mass, not mass-energy that judges gravitational attraction, so it would do no such thing to earths orbit, even if it received energy from somewhere else.
  5. Matterwave

    Matterwave 3,865
    Science Advisor
    Gold Member

    This is false, energy affects gravitation as well as rest mass.
  6. Really? I'm sorry I wouldn't have posted that if I hadn't heard it before, I'll have to look back to where I heard that, because I would have sworn I was right.

    EDIT: You're completely right, however I definitely picked that up from a previous thread here where I was swayed from my previous (correct) viewpoint, so I think someone here taught me wrong! :P
  7. Good lesson illustrated can't believe everything you read, even here.

    Some people get really bent when you disagree with them, tell them they are wrong, but unless it is done someone else may well learn the wrong thing.

    While we are on the subject of gravity, mass, energy and PRESSURE all have gravitational effects. And that includes dark energy and dark matter although we currently have little knowledge about just what they are.
  8. That all makes sense to me except the pressure part, would you mind elaborating?
  9. Gravitational reactions dictates how E works, it's just Sf into TMass and Bmass around a Scatter Matrix of E exchange of any Mass. This is a Presurfistic Event of Natural Occurrence where the (h) can be achieved. The end result is folic in Curve function between two given Masses. The W function into TMass and BMass (L) at h now becomes a Bmass and the Directional Force creates a Tmass (D). The Presurfistic Event is the exchange of E of 2 given Masses.
  10. Not to be rude, but, what?
  11. Elaborating on the previous posts you had the right idea and the function could also determine that outcome. I explained the example to you because it isn't One Dimensional anymore on x or y scales. The 2 Masses I was refering to explains you're hypothesis, but you need 2 colliding Masses to acheive this. As I said Lmass has a T and BMass and DMass has the same Masses it's the Presurfistic Event that occurs between the 2 Masses that determines the h exchange. I hope that explains the interjection
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