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The meaning of inertia

  1. Dec 1, 2004 #1
    Inertia has always bothered me in the sense of the actual mechanism behind this resistance to acceleration-why? I believe Mach had some idea that the gravitational attraction of the rest of the universe was behind it but did he manage to prove anything? Certianly Einsteins equivalence principle would suggest such a connection but I believe Einstein himself never found a real inertial mechanism. Any thoughts?
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  3. Dec 8, 2004 #2
    I presume the puzzler could be reversed: if one postulates existence of kinetic energy, then mass just pops up as a constant, and one can start talking about inertia. This is trivializing things. The more stuff you speed up, the more energy it takes. The "more stuff" is really "stuff with more inertia" or "more mass". We're not talking rigid body mechanics, but linear motion, for sake of simplicity.
  4. Dec 9, 2004 #3
    Newton's Bucket and the Higgs

    I've always been interested in the cause of inertia myself. In fact, many years ago when I was first introduced to Mach's Principle while studying General Relativity I liked the idea. But then in a book called "The Structure of the Universe" by Narlikar I read that Kurt Gödel had proven that Mach's Principle was mathematically incompatible with General Relativity.

    More recently while reading Brian Greene's "The Fabric of the Cosmos", I was surprised to hear Brian consider that Mach's Principle might still be compatible with GR after all to some extent. But then Brian goes on to say that it may not be fully compatible with GR, plus GR actually suggests that the effects of inertia may very well be present in an almost empty universe. I not sure how they can say that with any confidence because who's to say that GR would even still be valid in an almost empty universe?

    In any case, you might want to read Brian Greene's book. He talks about this topic in terms of Newton's Bucket. And it does appear to me that Brian suggests that inertia would indeed still exist in an almost empty universe.

    I believe that most recently the Higgs field is currently being given credit for causing both mass and inertia, these two properties are pretty much inseparable and are obviously intimately bound to the phenomenon of gravity (pun intended :biggrin:).

    I also believe that the Higgs field had something to do with causing the inflation of the Big Bang. Somehow it got caught in some kind of a weird energy well during inflation and never quite came out of that well. And that's why we have mass, gravity, and inertia today.

    That's my vague understanding of the ideas. Steven Pollock and Alex Filippenko (sp?) have a couple of educational videos avaliable at The Teaching Company. Pollock's video is on particle physics and mentions the Higgs field. Filippenko's video is on astronomy and talks about the cause of inflation in the last part of the course (his big course). Neither of these courses go into any of mathematical details but they are quite interesting none the less.

    Here's a link to The Teaching Company that has these videos: http://www.teach12.com/
  5. Dec 9, 2004 #4


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    They can find solutions of Einstein's equations that describe an almost empty universe and then see what the equations predict in that case. Since Einstein's theory defines spacetime, it's valid in any case that it can define.
  6. Dec 9, 2004 #5
    I understand what you are saying. But what I meant is that Einstein's theory itself is based on postulates that we assume to be true in our current universe. Some of those postulates may indeed not be true for a massless universe.

    I mean, prior to the deal with the Higgs field during inflation the postulates that Einstein's theory rests on may not have been valid. In other words, prior to inflation it could be that particles had no mass or inertia, and there was no such thing as gravity!

    In fact, if it is genuinely believed that the Higgs field gives rise to mass and inertia (i.e. properties associated with gravity), then the Higgs field may very well have given rise to gravity itself.

    I don't understand all this inflation business with the Big Bang. And I certainly don't understand how an entire field itself can get stuck in a potential well. But I've heard this theory from at least three very prominent physicists,.. Steve Pollock, Alex Filipennko, and Brian Greene to name a few.

    But my question is that if the Higgs was responsible for creating mass and inertia during (or just after) inflation, then I would think that that would mean that there was no such thing as mass, inertia, or even gravity, prior to the inflation event. Yet I've never actually heard any of these physicists address that issue. On the contrary they appear to continue to assume that gravity, mass and inertia still existed prior to inflation. But that seems to contradict the idea that the Higgs field is somehow responsible for these things I would think?

    I'm slowly learning the mathematics of quantum field theory. But this is going to take me years for sure since I have a lot of differential geometry and calculus of variations to learn first! I'm really interested in understanding how an entire field can get hung up in a potential well? I mean, I'd like to see that mathematical statement (and be able to read it!) :approve:
  7. Dec 10, 2004 #6

    Inertia is the resistance to change.

    I believe it arises from the interaction of particle fields with the basic fields underlying space/time. Since the particle fields have different structure and symmetry than the underlying fields, their interaction produces a resistance to movement and change. This resistance is called inertia.

  8. Dec 22, 2004 #7


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    I once heard a theory that the inertia of an electron was caused by its interaction with its own field. They got infinities when they first tried to calculate this (over 100 years ago), but the problem was similar to those encountered in early QED, and maybe it could also be fixed by renormalization. Maybe the inertia of most particles is caused by their interaction with their own gravitational field, and electrons really have no gravitational mass but only inertial mass due to their charge. This could be partly dismissed right away if the electron does respond to gravity, but even if so, there may be a way it could still work.
    Last edited: Dec 23, 2004
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