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Do physics professors still misunderstand Einstein?

  1. Mar 11, 2013 #1
    do physics professors still misunderstand Einstein??

    i registered at this site just to ask this question:

    why do physics professors still talk about gravity in terms of "pulling"?? i download podcasts of physics courses at Yale, Berkeley, etc... yet i always hear these guys say things like, " all the mass in the earth is pulling us down, every atom, cumulatively." As though gravity is a force exerted by mass upon other masses, when Einstein told us (almost a century ago) that this isn't the proper way to think about it. the earth's mass doesn't have any direct effect on us at all, actually; mass distorts *space*, and it is more correct to speak of space 'pushing' us down rather than the earth is 'pulling' us.

    if someone could please chime in and explain why this is, i would be grateful. it frustrates me so much! i'm no physicist, but have a passive interest and learn what i can. when i hear professors speak this way, as if they are ignorant of some of the greatest developments in physics, i just delete it right away. i refuse to listen to Newtonian depictions of gravity.... im not a historian!!

    and if anyone knows of some good (and accurate!) literature or anything on iTunesU please let me know. as i said, im not a physicist and don't have the benefit of asking professors or colleagues. im on my own, yet want to understand anyway.
  2. jcsd
  3. Mar 11, 2013 #2


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    They aren't ignorant at all and what you are requesting is very unreasonable. It is NEWTONIAN MECHANICS so why on earth would they present gravity in the framework of general relativity instead of Newtonian mechanics where gravity is indeed a force? You refuse to listen to Newtonian depictions of gravity? THIS is what's ignorant my friend. You have to learn the Newtonian view to not only appreciate the general relativistic view but also make sense of the physics in approximately Newtonian systems. You do realize that in everyday, mundane life Newtonian mechanics still reigns supreme? By your logic, we should skip learning classical electrodynamics and go straight to QED.
  4. Mar 11, 2013 #3
    No, physics professors don't misunderstand Einstein. But I think you are misunderstanding what physics is. Physics consists of a series of approximations to reality. These approximations get better but also tend to get very difficult.

    The first approximation to reality is Newtonian physics. It is a very succesful theory and is still used a lot. Whenever people build a house or build a car, they resort to Newtonian physics. They rarely resort to GR because GR is too difficult to work with and it's not really needed.

    The second approximation is relativity. But to understand relativity, you must first understand Newtonian physics very well. If you don't know what Newton's laws entail, then you have no chance in understanding relativity. Furthermore, relativity is only a useful theory in special cases (for example: when speeds are high enough). If you want to a ball falling towards the ground, then Newtonian physics is enough.
  5. Mar 11, 2013 #4
    im thinking of cause and effect here... as i understand it, and i could be wrong because i have no scientific training!, mass doesn't pull other mass toward it. the only thing mass has an effect on is the medium of space, and it is this distortion of in space that creates the phenomenon of gravity. i understand that Newton's equations still work all the same, but conceptually, it is the wrong way to talk about it. or do i misunderstand entirely?
  6. Mar 11, 2013 #5


    Staff: Mentor

    That isn't quite what Einstein said. He said it isn't the proper way to think about it if you're interested in finding a generalized description of gravity that covers all cases. If you're only interested in particular cases, the Newtonian description might be a perfectly good way to think about it. See further comments below.

    This isn't quite right. First, mass distorts *spacetime*, not space; including time is crucial, since the space curvature produced by the Earth, for example, is negligible; all of the familiar effects of the Earth's gravity are due to the way its mass distorts time, not space. Second, spacetime doesn't "push" on objects; it just provides a geometric structure through which objects move, and the presence of mass induces curvature in this geometric structure. Freely falling objects--objects moving solely under the influence of "gravity"--just follow the straightest paths they can in this curved geometry.

    (Objects which are not freely falling, such as you standing on the surface of the Earth, are not freely falling because something else is pushing on them; the Earth, in this case. That's the reason we feel weight standing on the Earth: the ground below us is continually pushing us upwards, out of the straight freely falling path we would follow if the ground were not there.)

    Newtonian descriptions of gravity are not just of historical interest. For almost all practical problems, Newton's laws are a very good approximation. It's only in a few extreme cases that the corrections due to GR are large enough to matter. That's why many physics professors still teach the Newtonian description: many people don't have either the need or the desire to learn the more accurate but more complicated GR description.

    If you do want to learn GR, that's great! But not everyone does, and physics professors have to be aware of their audience.

    A good layman's book on the subject is Kip Thorne's Black Holes and Time Warps. If you want to get into the math, you can try Sean Carroll's online Lecture Notes on GR. The math does require you to already have quite a bit of mathematical background, though: you should be comfortable with algebra, calculus, and geometry at a minimum.
  7. Mar 11, 2013 #6
    does mass have a mysterious property that pulls me down toward it, or does mass distort space which, as a result, 'pushes' me down?
  8. Mar 11, 2013 #7


    Staff: Mentor

    On the Newtonian view, yes. On the GR view, no. The GR view gives more accurate answers; but the GR view might not be the last word either. In fact, many physicists believe it isn't; that we will eventually develop a quantum theory of gravity that makes corrections to the GR view. Such a theory might also change the conceptual framework, so we can't say the conceptual framework of GR is the last word.

    On the GR view, it distorts spacetime. See my previous post.

    No. See my previous post.
  9. Mar 11, 2013 #8
    yes, ive read that mass distorts space, and space tells matter where to go. that is why there is such a thing a gravity. i just want to know why professors gloss over this, to the effect of leaving students thinking that gravity is a force of *attraction* that the earth exerts upon all of us. this doesn't seem to chime with what i read
  10. Mar 11, 2013 #9


    Staff: Mentor

    Because it usually works!!!

    It may not work in all situations, but the math is so much simpler that whenever it does work it is FAR preferable to use Newtonian gravity over General Relativity. A professor who jumped right in to GR without teaching Newtonian gravity would be doing his students an incredible disservice.

    Also, your idea that space pushes instead of mass pulling is wrong. That is not what GR says at all, and "push gravity" theories have been discredited for much more than a century. What GR actually says is that spacetime is curved, so inertially moving particles can accelerate towards or away from each other. The distinction between space and spacetime is critical, and, in fact, the acceleration that you feel on the surface of the earth can be more or less attributed to curvature in time rather than curvature in space.
  11. Mar 11, 2013 #10


    Staff: Mentor

    Because gravity is not either one thing or the other; it can be both. The Newtonian description of gravity as a force, and the GR description of gravity as spacetime curvature, are *models*. They are different ways of looking at the same thing. They are not mutually exclusive; you can use whichever one works better for your particular problem. The GR model gives more accurate answers, but it's also more difficult to use.

    Also, as I said before, the GR model is not the last word either. We might discover another still more accurate theory of gravity in the future that has a completely different conceptual foundation. So we can't say that the GR model of gravity as spacetime curvature describes "the way gravity really is", any more than the Newtonian model of gravity as a force does. Physics professors mostly don't go into all this; they teach whichever model is most appropriate for their audience.
  12. Mar 11, 2013 #11
    ok. i want to know what gravity is. what causes it. im not interested in mathematically describing its effects. im being philosophical. for all his genius, Newton didn't know the how or why of gravity, only how to describe it precisely through mathematics. Einstein took us a step further toward understand just what this phenomenon might be and how it comes about....and of course this is unlikely to be the last word on the subject!! but at least it's a more experienced, imaginative attempt at an explanation. it takes us a bit further toward an actual understanding.

    and no the earth is not pushing up on my feet! it is simply in the way so that 'space-time' can't direct me any further. im not physicist, but that doesn't mean im an idiot
  13. Mar 11, 2013 #12
    forget it. i guess mass just has an mysterious power to attract me to it's surface, akin to magnetism. the professors must be right. all this stuff about distortion of space-time must not be relevant to understanding what gravity is. ill be quiet
  14. Mar 11, 2013 #13
    Re: do physics professors still misunderstand Einstein??

    Terryl I think everyone in here would like to know the WHY about gravity but all that is known for sure is that it is related to mass. It isn't enough of an answer for me either, but I have never had anyone in my entire life be able to explain to me why gravity attracts or maybe we are just constantly accelerating through sometime but nobody knows why. They only know that the bigger the mass the more the 'force.'
  15. Mar 11, 2013 #14
    Because to an amazing approximation, treating gravity as a force is correct.

    An intro classical mechanics course deals with problems like, you drop a ball from 5 meters in the air, how long does it take to hit the ground? Do you want to treat this using general relativity? Or get an approximate answer that is good to, what, 10 decimal places?

    You don't have a deeper understanding of physics by not appreciating approximations.

    Also, Einsteins genius trumps almost any in history but there are countless physicists who understand GR better than he did, by this point.
  16. Mar 11, 2013 #15
    thank you. i didn't expect such an ardent defense of Newton on the matter of gravity. especially since he himself was perplexed by it and only claimed to describe its effects. and since gravity has been proven to affect massless photons, i thought the old way of talking about it was out. i thought science had gone a few more steps toward understanding the physical causes of gravity, by positing space itself as a medium, a fabric, that can be warped and that somehow can account for gravity. but apparently most people are satisfied to say it's just there and mass is the source. doesn't really add up to me, but im just a lowly non-physicist. i have no business trying to understand
  17. Mar 11, 2013 #16


    Staff: Mentor

    These are different things. "What is gravity?" is a philosophical question, not a scientific one. "What causes gravity?" is a scientific question, and the answer is "mass".

    That's not a very useful position to take, IMO. For one thing, if you don't look at the mathematical description of the effects, you won't know how accurate the various models are. See further comments below.

    So you agree that this is a philosophical question, not a scientific one.

    Sure, for the kind of understanding you're interested in. But again, you only know that it's a bit further toward an actual understanding because you have looked at the mathematical description of the effects, so you know that the GR description is more accurate.

    These are not contradictory statements; they are just different ways of looking at the same thing. If the Earth didn't push on your feet (if, say, you were made of neutrinos so you didn't interact with the Earth), then it wouldn't stop spacetime from "directing" you; you would free-fall right through the Earth (and neutrinos are in fact doing this all the time).

    No, you're wrong. It isn't the last word, but that doesn't mean it isn't relevant. For one thing, as I've already mentioned, viewing gravity as a "mysterious power" of mass will not give you answers that are as accurate as the answers you get from the GR view. But of course you only know this by looking at the mathematical description of the effects.

    The mistake you're making, IMO, is to insist that the professors must be either right or wrong; that there is some "way gravity really is", and either they're telling you what it is or they aren't. If you insist on viewing things that way, then the professors are wrong: "the way gravity really is" is *not* a "mysterious power to attract" things, and it's *not* "curvature of spacetime" either. We don't know "the way gravity really is".

    But the professors aren't trying to tell you "the way gravity really is". If they were, they would be philosophy professors, not physics professors. The professors are trying to describe a model, and it's a very useful one.
  18. Mar 11, 2013 #17


    Staff: Mentor

    Where did anyone say they were satisfied with that view?
  19. Mar 11, 2013 #18
    how many times do i have to say that im not looking for the easiest equations to calculate physics on earth? i understand that Newton's equations are still practical for most of the conditions we experience here. Ptolemy had accurate equations for predicting the movement of 'heavenly bodies', even though he still assumed everything out there revolved around the earth. clearly, he was wrong conceptually, theoretically. so was Newton. Newton believed in absolute time, didn't think of space as a medium so much as a basic emptiness, an absence.

    im tired of debating. i had a question, and most of the responders missed the point of it. adios
  20. Mar 11, 2013 #19
    Re: do physics professors still misunderstand Einstein??

    I agree with most of this except his question being philosophical in nature. He wants to know WHY. Not merely that it is. We all know that it is, but to tell him wanting to know more has no place in physics I do not agree with. The only fair response I believe is to say that we simply do not know why mass creates/effects/causes? 'gravity.' Newtonian physics are correct to a degree useful enough for most applications. I like the GR theory, I can understand acceleration. All this said, I think the only fair answer to his question is that we don't know why and on a personal level it is one of the driving 'forces' behind my interest in physics.
  21. Mar 11, 2013 #20


    Staff: Mentor

    And so was Einstein, if your criterion for "wrong conceptually" is what it appears to be (more on that below). At least, he was wrong conceptually unless it turns out that GR is the "final theory" of how gravity works, which is highly unlikely IMO.

    But I'm confused about how you determine that someone's theory is "wrong conceptually". How do we tell that Ptolemy was wrong conceptually? How do we tell that Newton was wrong conceptually? If it's because their theories weren't GR, why is that relevant conceptually? It's relevant if you're trying to get more accurate mathematical answers, but you said you're not interested in that. But GR is not the last word conceptually (at least, it's highly unlikely that it is), and we don't know what gravity "really is" conceptually, so how do we know Einstein was not wrong conceptually but Newton and Ptolemy were?

    I don't think we missed the point. I think we realized that the question is not a physics question, it's a philosophy question, but you keep on wanting to make it a physics question.
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