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B Some abnoxious questions regarding mass, gravity and spaceti

  1. Mar 28, 2016 #1
    I don't really understand energy-momentum...
    Regarding the fundamental fields in the standard model: Could the gluons in an atom (and the atom itself), ever be stationary to spacetime? I'm assuming not because that would seem like the atom didn't have gravity or ...whatever? (I can't really word the question, I mean like if it wasn't moving there wouldn't be a perturbation in the Higgs field or exchange of energy to slow the atom down)
    My thinking is (and this may be a misunderstanding in my own premise) that if everything is travelling at the speed of light by default, and gravity just constant exchanges of Higgs energy with the Higgs field (I presume through Higgs bosons?) that causes things to experience time and have mass...or is it just gravity?

    Is the equivilancy between mass and energy (M = E / c^2) due to the Higgs field?

    Also, are gravitons like the virtual photons of the Higgs field?

    Please forgive my ignorance and poor wording. Hopefully it's all not as silly as it sounds.
  2. jcsd
  3. Mar 28, 2016 #2


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    An atom can be stationary in space, in spacetime the question makes no sense (can you stay at 15:00?). Gluons in a nucleus don't have well-defined trajectories.
    That does not make sense at all.
    That is not true.
    That does not make sense.
    There are no "virtual photons of the Higgs field".

    I suggest to go back some steps, and start with proper introductions to the topic.
  4. Mar 28, 2016 #3

    Simon Bridge

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    No such thing ... you can be stationary wrt some observer, but iirc gluons are virtual particles. That is, they exist only as a step in calculations.

    Higgs is not associated with gravity ... lets see if I can find the reference:

    It's OK - lots of people make that mistake.
  5. Apr 2, 2016 #4
    Thanks for the replies.

    Ah, Higgs > Mass >
    Mass > warp spacetime
    warp spacetime > gravity

    I suppose I was thinking along the lines of having mass was like the Higgs field is like molasses and when you try and wade through it it slows you down. So when a particle tries to move through Higgs it experiences mass.
    ...And since spacetime is currently expanding, the Higgs field is expanding too? (Whatever that would mean) So even a static particle may not be completely static wrt something expanding?...perhaps just ignore that last thought if it has no value. The theme here is probably that I don't understand the concept of 'rest' and non-rest energy.

    On the topic of E2 = (p c)2 + (M c2)2 I'm a bit uncertain.
    Also, is all momentum relative? How does kinetic energy or momentum exist if movement is only real wrt to a second observer, wouldn't kinetic energy be a relative thing only then?

    [I'm sorry I have so much I don't understand, so this is going to be a bit of a mess]
    Is there a mechanism in the standard model that causes (just slow moving) M = E / c^2 ? Is there any deeper understanding or explanation of how mass warps spacetime? (or is that pretty much as far as we can analyses the fabric of reality) I accept that energy is radiated away from orbits with gravitational waves, but is that purely in the form of the molasses analogy of the Higgs field decaying the orbit?
    (I'm trying to think way back to HS here) As I understand it, even if there was no Higgs field, Energy or Mass would still wrap spacetime and some gravity would still exist? I don't know how it is derived but I remember there is a formula for relative mass, could you then say that for all intensive purposes there two components of mass? One from the energy of the gluons at rest or static to the Higgs field, and one that's like a relativistic mass? Like if I'm moving really fast wrt the Earth, the Earth will see my mass increase?

    Oh, I must have not processed something I read that was written flippantly; I thought I heard that particles were all like photons, and travelled at the speed of light, and it was mass and interaction with the Higgs field that slowed them down and made them experience time and mass. But I suppose since all particles except photons, gluons and gravitons have rest energy anyway that can't be true.

    Cheers for your understanding Simon!
  6. Apr 3, 2016 #5


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    Then start with one topic, please. Like classical mechanics. Answering questions to quantum field theory (Higgs mechanism) doesn't really help if you do not understand the basics.
  7. Apr 3, 2016 #6


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    The momentum is a vector, it's relative even under 3D rotations (leaving aside Special Relativity)...

    "Exist" is a bad word...(?)... I have never seen a momentum neither have I seen Energy. They are certain quantities which are conserved when we measure them. We measure them in our reference frame. A different reference frame (again even in classical mechanics) will measure different values for those...
    Take for example a train moving with velocity [itex]\vec{V} = V_0 \hat{x}[/itex]. A passenger inside the train holds a ball of mass [itex]m[/itex]. He shoots the ball ahead with velocity [itex]\vec{u} = u \hat{x}[/itex].
    In his reference frame, the ball is having kinetic energy: [itex]E_{pass} = \frac{1}{2} m |\vec{u}|^2= \frac{1}{2} m u^2[/itex] and momentum [itex]\vec{p}_{pass}= m \vec{u} = m u \hat{x}[/itex].
    Now in your frame, let's suppose you are outside the train, the ball is not moving with velocity [itex]\vec{u}[/itex], but with velocity [itex]\vec{V} + \vec{u}[/itex]. As a result, the energy you'll measure's going to be:
    [itex]E_{you} = \frac{1}{2} m |\vec{u}+\vec{V}|^2 = \frac{1}{2} m (u+V_0)^2 [/itex] and momentum [itex]\vec{p}_{you}= m (\vec{V}+\vec{u}) =m (V_0 + u) \hat{x}[/itex].
    So you and the passenger are not going to measure the same momentum and kinetic energy. What you can both however see is that both those quantities (if nothing else is happening) are conserved. If the ball for you had energy 5J, it will have energy 5J after 10seconds. For the person on the train it might be 1J, but in his frame the ball's energy will remain 1J after 10 seconds... etc...
    Rotations can also alter the momentum you measure, but not its magnitude.

    Nevertheless, in special relativity you can construct a similar thing to the magnitude of a vector for 3D rotations. But you only have 4-vectors. Well the combination that creates such an invariant for the analogue to momentum in SR is the:
    [itex] E^2 - |\vec{p}c|^2 = const[/itex]
    So for one observer the energy might be E=3 [energy units] and the momentum would be p=2 [energy units/c]... and for some other observer the energy might be E=5 [energy units] and p=2 sqrt(5)[energy units/c]

    that constant is the "rest mass", or the "mass". It's in fact the energy your particle would have if you sent your momentum to zero [itex] |\vec{p}| \rightarrow 0 [/itex] (or if you did a Lorentz Transformation that sent you to a reference frame where the body you consider is at rest)...

    Yes... it's called General Relativity and it's the theory that currently describes gravity to our best of understanding and precision of measurements.

    You should give up (I saw you used that twice) on the idea of a Higgs molass through which particles move and gain mass. It's supposed to be an analogy and not treated as a general fact on which you can create (sensible) questions. Most of the mass of our every-day particles doesn't come from the Higgs Mechanism.

    It's good that you don't know how it's derived... it would be best for you to totally forget of that it (relativistic mass) ever existed. Call it Energy.

    Yes, that's the analogy of the HIggs Molass about... in the Standard Model the elementary particles would be massless but due to the Higgs they gain their mass. It's a flaw of the analogy however.
  8. Apr 4, 2016 #7

    Simon Bridge

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    ... that is a common enough mistake.
    Did you read the article in the liink in post #3?

    The rest of your post contains other very common misunderstandings related to the way pop-science reporting works.

    Hopefully you have read the article in the link in post #3 and you now know better.

    The idea of being stationary wrt space-time ... hmmm... at this stage that is not a useful way for you to be trying to think. Objects move with respect to an observer. You cannot talk consistently about motion without referring to who is measuring the motion. Space-time itself is not an observer.

    ... looks like you read the article in the link. Well done. It may be better to address questions about this article in a different thread.

    Starting from the end: yes - kinetic energy is relative.
    Kinetic energy and momentum exist because of the work needed to bring an object to rest with respect to the observer.
    If you have been struck by a baseball you will easily believe in the existence of kinetic energy and momentum.
    Saying that something depends on your point of view, in physics, is not the same as saying it is imaginary or made up.

    What education level are you trying to understand this all at?
    No physics since High School?

    There is nothing special about the energy of a slow moving object compared to that of a fast moving object. It is just that when the numbers are small compared with the speed of light, like they are in everyday physics, we can make some approximations. The kind of physics you learned in mostly HS does this, which is why it is easy to get confused when you talk about GR and Higgs.

    The "mass warps space-time" is properly "space-time curves in relation to the distribution of energy within it" ... mass happens to be what we call the various really dense blobs of energy.
    A "deeper explanation of how mass warps spacetime" would be "a model that explains all mass in terms of more fundamental laws" ... like the HIggs mechanism does for fundamental particles.
    This is difficult because of how much mass is tied up with gravity, and a more fundamental origin for mass would involve a quantum theory of gravity ... which we don't have. So the short answer is no: we are stuck, for now, with the description of mass as the rest energy and energy density warping space-time.

    The molasses analogy has nothing to do with it.

    Higgs has nothing to do with gravity. I had hoped you'd have abandoned the idea after reading the CERN article.

    This sounds a bit like you are thinking of inertial vs gravitational mass.
    See discussion: https://www.physicsforums.com/threads/difference-between-gravitational-and-inertial-mass.689095/
    ... also others.

    Also see:
    (The overall article also covers origin of mass and other issues.)

    But note: gluons do not have mass - so they cannot be "at rest or static" wrt any observer and do not interact with the Higgs field.
    The inertial mass of an atom, and therefore of all non-dark matter (we don't know about dark matter) gets it's mass via the mass of the nucleus, which is primarly made from the energy stored in the strong nuclear field. This can be thought of, in a hand-wavey way, as the kinetic energy of the quarks and gluons.

    Lastly: "relativistic mass" would be ##m_r = \gamma m## where "m" is the "rest mass"... you may be thinking that maybe gravitational mass increases with relative speed? Say something like ##F=GMm_r/r^2## for an object mass m moving at high speed past a stationary object mass M.
    See: https://www.physicsforums.com/threads/does-increased-velocity-increase-gravity.74477/
    ... and other discussions in these forums.

    Technically - ##m_r## is called the total energy these days and we write, for arbitrary units: ##E=\gamma mc^2## ... notice this reduces to the famous ##E=mc^2## for small speeds. (##\gamma = 1/\sqrt{1-(\frac{v}{c})^2}##)

    If it were not for the Higgs mechanism, all fundamental particles would be massless ... so they would all travel at the speed of light.
    The Higgs field being likened to treacle or something is classic poetic licence from people trying to describe a subtle effect in ways better grasped by the general public. The trouble with this approach is that the reason we need the subtle physics in the first place is because the more easily grasped stuff simply does not work for these things. Thus the effort was doomed from the start.
    Treat the description as poetry designed to give a feeling without conveying any understanding.
    It's pretty and makes you go "wow", which is it's job.
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