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

Possible stupid question

  1. Apr 12, 2010 #1
    How does the standard model reflect inertial energy ?

    The following puzzles me-

    I am reliably informed that the entire milky way is moving through space towards a nearby galaxy cluster at a heady speed of 1000 Klm per second. I assume this scenario is repeated all across the Universe with billions of galaxies all moving in relation to each other, much like atoms in a gas ?

    Now in order to produce this motion it must have taken a huge amount of energy ? I don't have the maths skills to work out how much energy it would take to accelerate something as heavy as the milky way to 1000 Klm a second, but I'm guessing it's a pretty huge number ?

    Point being, that if the laws of thermodynamics are universally true then the energy MUST still be there somewhere. Mustn't it ? It's not like it can 'go outside' the Universe ?

    So if this vast amount of energy is still there in the form of inertial or potential energy, and energy (on a Universal scale) is the same as mass.. where is it in the standard model ?

    If anybody can give a 'plain english' answer I'd be most grateful, because it's something that has puzzled me for a while. Thanks.
     
  2. jcsd
  3. Apr 12, 2010 #2

    DaveC426913

    User Avatar
    Gold Member

    "Inertial energy" is an oxymoron. Inertia is what allows objects to (continue to) move without energy.

    The energy is there in the form of kinetic energy in the motions of the galaxies.

    In a very loose nutshell: the Big Bang threw the balls up in the air, where their potential energy was maximum, they are falling down, trading potential energy for kinetic energy as they fall.
     
    Last edited: Apr 12, 2010
  4. Apr 12, 2010 #3
    Thanks, I get that. I guess to rephrase the question- How does kinetic energy figure in the overall mass-energy budget for the Universe?
     
  5. Apr 12, 2010 #4

    DaveC426913

    User Avatar
    Gold Member

    Sorry, then I don't know what you're asking. The kinetic energy figures in as coming from the potential energy of the galaxies being separated in the first place.
     
  6. Apr 13, 2010 #5

    russ_watters

    User Avatar

    Staff: Mentor

    If you mean fractionally, it is not a very big fraction of the total energy.
     
  7. Apr 14, 2010 #6
    Thanks, could you tell me where I might find out what that fraction is ?
     
  8. Apr 16, 2010 #7
    Anybody ? I can find plenty of estimates of the breakdown of all other forms of energy in the Universe, but not one that mentions kinetic energy. Does anybody know of one ?
     
  9. May 1, 2010 #8
    Hmm, either I've stumped you guys, or my question really IS stupid. But it's a shame either way because I believe Kinetic energy may hold the key to some mysteries.

    Thing is, everything we know about kinetics, motion etc is from Newton right ? But if you play with a Newton cradle here on earth.. well, it's already got a shedload of kinetic energy by virtue of moving at 1000 klm/sec already. So any observations based on that and then expanded to other parts of the Universe without the same initial conditions can't be guaranteed to be 100% accurate. Can they ? The starting conditions are not the same. I'm not saying Newton was wrong, simply that his laws only work for local conditions.

    Take the pioneer anomaly, I strongly suspect the effect is being caused because they are one of the few man made things we can measure that are actually deviating significantly enough to be noticed from their initial kinetic profile, ie- our 1000Klm/sec baseline.

    The reason it works out as (C x the Hubble constant) is because the Hubble constant is a measure of increased kinetic energy difference. Things farther away are traveling faster = more kinetic difference with respect to us and our baseline kinetic energy level.

    That's why I wanted to know about Kinetic energy. Because I think it's a prime suspect for a lot of unexplained stuff. I strongly suspect it has a tiny but real effect on space-time, we have just never noticed because our experiments are skewed.

    Then again, I'm probably stupid :)
     
  10. May 1, 2010 #9

    russ_watters

    User Avatar

    Staff: Mentor

    Not stupid, just irrelevant, so it isn't something that scientists have probably ever figured on before. You can give yourself a rough order of magnitude estimate though:

    -Use e=mc^2 to calculate the energy equivalent of earth's mass
    -Use the kinetic energy equation to calculate the kinetic energy due to its motion through space (pick whatever speed you want from whatever frame)

    Compare the two.
    I'm not quite sure what you're getting at, but yes, Newton was wrong about how velocities are added. The correct method for velocity addition comes from Einstin/Lorentz. But the basic principle of relativity is the same: the laws of the universe are the same for anyone, so if you know the starting conditions, you can calculate the outcome. A Newton's Cradle sitting on a table, in a moving car, in a plane, or on the spinning surface of a pulsar all behave according to the same laws.

    You really are barking up the wrong tree here. If you do the calculation I showed above, you'll see the effect of kinetic energy on the total is many, many orders of magnitude smaller than the mass. The Pioneer anomaly is far too big (or we wouldn't have noticed it) to be a reslt of not figuring the kinetic energy of the solar system.
     
    Last edited: May 1, 2010
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook