Why vs. How?

Discussion in 'Physics & Math' started by Carcano, Jun 1, 2008.

  1. Carcano Valued Senior Member

    Recently I was flipping through a science mag and came across this article about gravity.

    There was one line in there that caught my attention:

    "We understand 'how' gravity works but not 'why' it works."

    How is this distinction made? It seems to me that in physics especially there will always be some overlap between the two questions???
    Last edited: Jun 1, 2008
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  3. Oli Heute der Enteteich... Registered Senior Member

    Physics only goes for the "how".
    The "why" is metaphysics....
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  5. Carcano Valued Senior Member

    It could be that even this is not yet true, as a few anomalies indicate:

    "There are some observations that are not adequately accounted for, which may point to the need for better theories of gravity or perhaps be explained in other ways.

    1. Stars on the outskirts of galaxies are moving faster than they should. Also galaxies within galaxy clusters are moving faster than they should. Dark Matter and MOND have both been proposed as explanations.

    2. The expansion of the universe seems to be speeding up. Dark Energy has been proposed to explain this. A recent alternative explanation is that the geometry of space is not homogeneous (due to clusters of galaxies) and that when the data is reinterpreted to take this into account, the expansion is not speeding up after all.

    3. The Pioneer spacecraft seem to be slowing down in a way which has yet to be explained.

    4. Various spacecraft have experienced greater accelerations during slingshot maneuvers than expected.

    5. An apparent frame dragging effect has been measured by Martin Tajmar and others which exceeds that predicted by General Relativity by many orders of magnitude."

    I can never understand why scientists just make stuff up, like undetectable dark energy/matter...just to make the equations work out.
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  7. Enmos Registered Senior Member

    What is the difference ?
    The "how" is why it works.. right ? :scratchin:
  8. Oli Heute der Enteteich... Registered Senior Member

    I'm trying to think of a simple example.
    (But it's late and I'm knackered).
    How about the photo-electric effect?
    We know how it works, because there's only a set energy amount that will cause the jump from level to the next.
    But why is that energy level that particular value and not any other?
  9. Enmos Registered Senior Member

    Ah ok, I see..

    But aren't those kind of things unanswerable ?
    Why is the speed of light in a vacuum 299,792,458 meters per second ? Why not 300,000,000 meters per second ?
    Isn't the answer 'just because' ?
    It's like asking why you were born in the country you were born in..
  10. Oli Heute der Enteteich... Registered Senior Member

    Damn, an even simpler example!
    So far as we can tell at the moment the answer is "just because".
    But there's hope...
  11. Enmos Registered Senior Member

    Yep.. hope lol
    I'm not going to wait up..

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  12. Carcano Valued Senior Member

    Theists love those 'universal constants'.

    These are values that must stay within an extremely narrow range...otherwise the universe could not support any potential life.
  13. Enmos Registered Senior Member

    Yea.. God did it.
    Which is the main reason we have to keep hoping that we explain the why's some day

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  14. Carcano Valued Senior Member

    Heres Dr. Stern's response:

    "What might be a satisfactory answer to a question like "why does gravity exist"? If the question can be rephrased "can we deduce the existence of gravity from more fundamental laws?" the answer seems to be no.

    Gravity seems to be one of 4 fundamental forces in nature, the other 3 being electromagnetism, the strong nuclear force (holding nuclei together) and the weak nuclear force (mediating between neutrons and protons). Each is independent.

    A more profound question is the following. Each type of force is proportional to some "charge" carried by elementary particles. For gravity, that charge is mass. Why then is the mass of an object also proportional to its inertia, to its resistance to changing its velocity?

    This brings in general relativity, which is not my field. However, I do not think Einstein "explained" this proportionality--he just asserted that it, too, is a fundamental law of nature, and then deduced from it certain interesting consequences, which experiments have confirmed."
  15. oneposthopefully Registered Member

    Semantics. The why is an unexplained how, as soon as we know why something is, it changes to how it is. Why is the sky blue?

    "The sunlit sky appears blue because air scatters short-wavelength light more than longer wavelengths. Since blue light is at the short wavelength end of the visible spectrum, it is more strongly scattered in the atmosphere than long wavelength red light. The result is that the human eye perceives blue when looking toward parts of the sky other than the sun."

    -Diffuse Sky Radition, Wikipedia

    Why do we see only see that part of the electromagnetic spectrum?
  16. Dywyddyr Penguinaciously duckalicious. Valued Senior Member

    Not so.
    "How" is not synonymous with "why".
    They are fundamentally different questions.

    The two halves of your sentence seem to contradict each other.

    Because our eyes only work in that portion of the spectrum.
    Now the question is "why do our eyes not work in other portions?"
  17. CptBork Robbing the Shalebridge Cradle Valued Senior Member

    I remember when I was a young teen reading some layman's book about modern science, and it mentioned how Einstein's General Relativity "explained" gravity. One of my high school physics teachers also discussed this, and drew us a picture of a ball rolling on an indented mattress (representing curved spacetime), showing how objects tend to roll down to the bottoms of the indentations. To him it seemed completely obvious how such a picture would explain the workings of gravity, until I pointed out the limits of the analogy. On a mattress, you have an external gravitational force due to the Earth, and this is what's pulling the ball down, not the indentations themselves. In curved spacetime, where's the external force coming from? My physics teacher was as baffled as I was, and we wondered then what the heck was actually going on and just how it was that Einstein's curved spacetime was supposed to "explain" gravity.

    I figured it would require a mathematical understanding of General Relativity before one could properly understand how a curved spacetime could cause things to move, even if they start off seemingly at rest (i.e. it's easy to picture a moving satellite being deflected and redirected by curved space in a smooth orbit, but what about a helicopter that starts off at rest and then falls to the Earth?). It took me a good 7 or 8 years of hard work after that point before I was finally ready to learn the mathematics of General Relativity, but I toughed it out, took the course and passed it. And in doing so, I had a big revelation that aided my philosophical understanding of physics enormously.

    Theoretical physics doesn't say why things are the way they are, nor does it provide a simple, intuitive means of explaining and deducing all these concepts from common sense principles. Yes, the goal of theories like String Theory is to reduce all the content of physics to one single equation or set of equations that can be applied to any situation in the (known) universe, but these equations are taken as fundamental first principles in the theory, with no explanation whatsoever as to why they work or whether there's an even deeper underlying principle behind it all. And that's exactly how it is in GR too. Just like when Newton gave his gravitational equation, and candidly admitted he had no idea why this equation worked, Einstein also presented gravitational equations and shrugged his shoulders as far as why they worked the way they did. All he knew was that these equations gave a description of gravity which looks almost exactly like Newton's in weak gravitational fields, conforms to the requirements of Special Relativity (Newton's gravitational law doesn't), and predicts measurable deviations from Newton's predictions for various gravitational phenomena.

    Yeah, it's very frustrating to watch them make the same straw man arguments over and over again. As is the case in nearly all their arguments, they neglect (either deliberately or mistakenly) the most important detail. The vast majority of physicists never said life would be impossible if the supposedly fundamental constants were shifted in value. They're saying that life as we know it would be impossible. The particles, atoms and molecules that form in the universe would all have different properties from what we observe, and would lead to different chemical structures. To prove that such structures couldn't lead to life with present technology, we'd require a galaxy's worth of resources to assemble the required computing power. I used to get frustrated seeing all these creationist hardliners making such junk arguments against science for consumption by a very poorly informed public. I don't mind it so much anymore, because I realized some of these people don't want our help to set them straight. They'd prefer to let themselves be treated like babies and get screwed over by their spiritual authorities, so I figure I might as well just take advantage of these people in the same way if ever need be.
  18. BenTheMan Dr. of Physics, Prof. of Love Valued Senior Member

    I think this is a very important rephrasing of the question. ``Why does gravity work?'' is a bit meaningless

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    I think you're pretty mistaken in your opinions of science. Did Einstein `just make up' general relativity to make his equations work out?

    The point is, as physicists, we make some set of observations about the universe. Then we try to understand those observations in terms of theories that we have already ``proved''. (Here ``proved'' means that we have successfully predicted past observations with the same theories.) One of two things happen: either the old theories work, and we can understand the observation in terms of them, or the old theories do not work, and we need to modify them somehow. I say ``modify'' and not ``throw away and start over'' because the old theories are obviously of some value, because we've already shown that they work with some observations.

    Take dark matter, for example. The spiral arms of galaxies are much too long if we only consider the stars that we can see. However, if there were more matter, which we couldn't see, then things would work out quite nicely. Alternatively, one can change gravity.

    We're left with two courses, then. Invent a new particle which no one has observed yet, or modify gravity. Both courses have their merits, and both have been tried. And, I should point out, one course is no better or worse than another course. Which field you choose is up to personal taste.

    Now we invent a new theory (dark matter or modified gravity), and try to understand how it works in terms of the old theory (general relativity).

    This is how science works.
  19. BenTheMan Dr. of Physics, Prof. of Love Valued Senior Member

    I should also point out that modified gravity is pretty much ruled out at this point. Recent observations of the Bullet Cluster were pretty much the nail in the coffin.

    In the interest of fairness, though, I will say that modified gravity theories aren't completely dead. One can still modify gravity in such a way that can explain the Bullet Cluster, however, what you get is a theory that is the same as general relativity + dark matter. Conversely, you can modify gravity AND add dark matter, but then you have to explain why you would want to rape one of the most beautiful theories we've come up with as humans for no real reason.

    The ultimate arbiter will be direct detection: if we directly detect dark matter, then we know that the dark matter solution is probably right. This doesn't mean that gravity isn't stil modified somehow, it only means that we can explain all of our observations with dark matter.
  20. Nasor Valued Senior Member

    I suspect he meant that we can very accurately describe what gravity does, but not the mechanism by which it does. Kind of like knowing that airplanes allow people to fly, but not understanding how the engines work.
  21. martillo Registered Senior Member

    I completelly agree with this.
    If "we" are getting too much strange predictions it could be time to think if there could be something wrong in "our" current theories.

    For example the "Universal Gravity Force" formula could have some other factor wich would have neglihible effect in a planetary scale and would work at galactic scale.
    But you know the problem (not meaningless) is that we could be leaved to admit that for example Einstein was wrong and seems that the psychological problem is much bigger than the Physical Problem.
    I think is much more difficult nowadays to admit Einstein wrong than to find a right formulation of the Gravity Force.
    As BenTheMan wrote:
    Last edited: Aug 27, 2009
  22. martillo Registered Senior Member

    I also think your "why vs how" question is important in the sense of looking for a theoretical determination of the formulas of the Forces of Nature. All the Forces' have been determined experimentally with observations in their effects in natural or experimental phenomena but we don't know if there is a theoretical reason for them to be that way. If we would know the reason we could know the exact and complete formulas.

    In the case of the Newton's Gravity Force it is important to note he developed his formula with the observations of the planets, moons, etc behavior but not the Galaxies' behavior which he didn't know and didn't take into account (Am I wrong?).
    I don't know who gave or when it was given to Newton's formula the name "Universal Gravity Law". May be at the end that law is not universal and actually could need other factors to be really universal.
    As I wrote in the previous post: "the "Universal Gravity Force" formula could have some other factor wich would have neglihible effect in a planetary scale and would work at galactic scale".

    The theoretical determination of the Forces' formulas could be great but I think it would not be possible because there would be other "why" to know like why the Universe is as it is and not in other way...
    Last edited: Aug 27, 2009
  23. AlphaNumeric Fully ionized Registered Senior Member

    I never understand two common traits in cranks :

    1. They whine that mainstream physicists are 'close minded', that mainstream physicists denounce anything novel or 'out there' or which says their previous work is wrong.

    2. They whine that mainstream physicists suggest novel and 'out there' things which completely rewrite previous work.

    It's Catch 22. I see people who say "Dark matter? That's BS!" then in the next sentence say "I suppose the notion of an aether!". Wait, so mainstream physicists suggesting the existence of a previously unseen substance due to experimental suggestions is crazy but you suggesting the existence of a previously unseen and still unseen material is fine?! What?!

    It is naive, utterly staggeringly laughably naive, to think we have seen all the stuff in the universe. The suggestion only a small fraction of the universe is easily detectable, ie you can literally see it, is not daft to me, it's quite a sound hypothesis to make if you ask me. And physicists aren't saying "It can only be explained by dark matter, any other explanation will never be entertained!", they say "It can most easily be explained by dark matter, all other explainations require more and more convoluted reasonings and by Occams razor we'll go with dark matter until such time, if such a time ever occurs, that the phenomena simply cannot be explained by matter which doesn't interact with light".

    Of course that's a bit of a mouthful for a news show to say so they don't. And then cranks start whining.

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