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

Is existing relativity 100% correct, or are we waiting for something better?

  1. Oct 20, 2012 #1
    Trying to understand what members of the forum feel about the correctness and completeness of existing relativity theory.

    Are there sufficient grounds to consider that existing relativity theory, as formulated by Einstein, is the best possible description of the real Universe we live in (making allowances for minor uncertainty)? Or is there significant doubt about that?

    Two guiding thoughts on this which I have seen in this forum and outside:
    - Quantum theory and GR are yet to be reconclied. Both are great theories well accepted by scientists and able to make good predictions, but there still isn't a generally accepted 'quantum theory of gravity'
    - There are many opinions but little concensus among experts, esp. in SR, about the resolution of paradoxes and explanations of experimental observations

    A relevant quote by Einstein [The Meaning of Relativity, 6th Ed, 1955]:
    "In my opinion the theory presented here is the logically simplest relativistic field theory which is at all possible. But this does not mean that nature might not obey a more complex field theory. More complex field theories have frequently been proposed...

    In my view, such more complicated systems and their combinations should be considered only if there exist physical-empirical reasons to do so."

    My question is, with 50+ years of experiments and observations since the above statement, are there enough reasons to do so?
     
  2. jcsd
  3. Oct 20, 2012 #2

    Bill_K

    User Avatar
    Science Advisor

    As a classical theory, general relativity has been 100 percent successful. There is excellent agreement with observation.
    This fact has been vastly overhyped. Quantum gravity is an eventual goal, for sure, but there is no pressing need for it at this point. Even semiclassical effects like the much-discussed Hawking radiation are far too small to actually observe.
    No, if you're implying that there are some paradoxes that have not been explained, this is quite untrue. Some observations have not been completely understood, like the jets emitted by black holes, but there is no reason to think this represents a shortcoming of the theory.
    Alternative theories are constantly being considered - this is the way science works. There is presently no reason to seriously consider them.
     
  4. Oct 20, 2012 #3

    tom.stoer

    User Avatar
    Science Advisor

    I don't agree.

    From an experimental = phenomenological point of view you are right, but not from a theoretical one. We know that quantum feild theory on top of classical general relativity is inconsistent, and we know that quantization of general relativity using 'naive' methods developed for quantum field theory is inconsistent, too. Therefore to complete the theoretical description of the world we need the completion of the standard model including something like 'quantum gravity'.

    There are some approaches which do noit deviate too much from both GR and quantum field theory, especially LQG and Asymptotic Safety. Both try to construct a consistent theory of quantum gravity w/o throwing everything on the heap, but simply via careful inspection, extension and completion of rather well-known but rarely applied ideas from standard quantum field theory.

    Of course there is the problem that due to the lack of experimental guidance one is not able to phenomenologically assess the various approaches (there are many more than LQG and AS) and therefore we may very well be in the situation that there could be more than one candidate theory for quantum gravity. But as I said: knowing that naive approaches to quantum affects involving gravity blatantly fail, there is no other way but to consider a theoretical completion.
     
  5. Oct 20, 2012 #4

    Dale

    Staff: Mentor

    There is no such thing as a scientific theory which is accepted as 100% correct, since we have not yet made 100% of all possible observations.

    I think this is wrong. The disagreement among experts about the various SR "paradoxes" is not substantive. It is simply that different experts prefer one explanation over another for various pedagogical or interpretational reasons. Substantive disagreements come from novices or others who don't understand SR, and they are simply wrong.

    Also, a lack of consensus on an internet forum cannot be taken as demonstrating a lack of consensus in the scientific community. You will never get consensus on the internet, even when the issue is completely accepted and understood by the scientific community.
     
    Last edited: Oct 20, 2012
  6. Oct 20, 2012 #5

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2016 Award

    The topic of this thread starts off with a non-existent concept. As DaleSpam has pointed out, there's no such thing as 100% correct in science. Point to me ONE scientific theory that is 100% correct.

    We are trying to discuss something based on a premise that has not been shown to be valid. Thus, this is another "When did you stop beating your wife?" question.

    Zz.
     
  7. Oct 20, 2012 #6
    I wouldn't know why you think that there is any issue with SR (except of course that it does not account for effects of gravitation on time and length measurements; that is not an issue but a simple fact).

    Relativity theory as formulated by Einstein (in 1916) is effectively "passé" (although some physics teachers don't seem to be aware of that); what is currently taught as "General relativity" is a subtly different theory. This is explained on the bottom half of the following physics FAQ page:

    http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_gr.html

    That changes nothing for QM but it may change the discussion of paradoxes, as you can see on the first half of that page.
     
  8. Oct 20, 2012 #7

    bgq

    User Avatar

    Hi, Please note the followings

    1) 50 years is a small period of time in history of sciences to make scientists 99 % confident of some theory.
    2) All what we do in physics is to try to describe how things "appear" to behave, we cannot know how things "really" behave. Thus, our theories just give consistent description that seems in agreement with what we observe, but the whole story may be completely different; that is, someday (may be 100 years in the future) we may have experiments that violate our current physics, and so new improvements are needed. In short, "Real physics" could not be known, all what we can do is find some relationships that are in agreement with our experiments.
     
  9. Oct 20, 2012 #8
    Why would we ever think that we have found the final absolute truth in all regards? Many have thought that about many things in the past, only to finally have someone expand our collective knowledge base further than most thought possible.

    Putting the sun at the center of the universe in the heliocentric model also explained all that they could observe at the time, until we built better telescopes that first taught us that our solar system is moving within the galaxy, and then later that we were but one of very many galaxies, each with its own path through the universe.

    But at any moment in time we have the best we have, so we let it serve to explain the things we see and to predict further things--until we are able to observe new things that don't fit the old model. So we will once again be either upgrading the one we have or replacing it with a better one.
     
  10. Oct 21, 2012 #9
    All theories are just models of reality, whether they be material or mathematical constructs.

    In so far as the model works well enough for our purposes, it can be regarded as 'good'. One that's better in the sense of being more accurate isn't necessarily more useful. I don't need SR or QM to play snooker.

    IMO the only way you can build a 'perfect' model would be to use the same materials and scale as the original. So in that sense, no theory is ever going to be 100%
     
  11. Oct 25, 2012 #10
    we experience the universe through our senses, and physics is an attempt to understand our universe. you must remember that all of physics is a human construct, it exists only in the human mind.

    Also, the validity of relativity has been proven beyond doubt when it comes to experiment. If an experiment casts doubt on relativity, this means that the experiment has been poorly conducted.
     
  12. Oct 25, 2012 #11

    jtbell

    User Avatar

    Staff: Mentor

    I would not say that. Rather, I would say that the validity of relativity has been confirmed within the limits of precision of our experiments so far. These limits may be very very broad, but there are things that we have not tested, and there is always room for more precision. There will always be "wiggle room" for still more-precise experiments that might discover violations of relativity as we know it. People actually do experiments on this, and theorize about what sorts of things to look for. This usually comes under the heading "violations of Lorentz symmetry" or something like that.

    If we do discover such violations and have to come up with a new theory to "replace" Einstein's relativity, that theory will still have to behave like Einstein's relativity in the areas that we've already tested.
     
  13. Oct 25, 2012 #12
    Exactly - Newton's theory was tested for a longer time, it had similarly (not really) been "proven beyond doubt when it comes to experiment."
     
  14. Oct 25, 2012 #13

    russ_watters

    User Avatar

    Staff: Mentor

    That sounds misleading: When the error margins were tightened in the experiments, Newton's theories were found to be proven wrong. This has not happened with Relativity.

    What you said at least implies that Relativity is in the same boat today as Newton's theories were in 1700. But Relativity's boat is much better constructed. Its level of uncertainty is much smaller.

    It is a mistake to use longevity as a measure of accuracy, as you have implied.
     
    Last edited: Oct 25, 2012
  15. Oct 25, 2012 #14

    Dale

    Staff: Mentor

    This is a key point. Just like the advent of relativity did not stop people from learning and using Newtonian mechanics within its domain of validity, so any future theories will not stop people from learning and using Relativity within its domain of validity. It is here to stay.
     
  16. Oct 25, 2012 #15
    Special relativity is derived by the two postulates alone, some geometry and maths. If the two postulates are correct, then special relativity is correct.

    1. Light(photons? lightbeams?) in a vacuum away of any gravity field will ALWAYS travel at C in all inertial frames of reference.
    2. The laws of physics are the same in all inertial reference systems.

    This is very simple maths/geometry and a very clear mind(or a lot of effort as in my case) which leads to the formulas of SR.
    (there are some other assumptions one makes, which go deep into details about space itself)

    The issue i see, as someone who does not understand QM or GR fully yet, is that it seems to be a very naive view of photons we use to derive the formulas.

    You could assume tenis balls traveling at C always, and you would get the same formulas. I derived the formulas using tenis balls traveling at C always basically.
    But photons are not just tenis balls. They can act very strange under certain circumstances even if there is no gravity.

    It's not just their wave character, but also all the strangeness you see in experiments like the double split experiments, double-double split experiments, elitzur-vaidman bomb tester, delayed choice quantum eraser experiments and more.


    If i remember right, i read Einstein hated the break of the wave function, because all of the sudden, while you calculate the path of a photon using a certain function, you cut one part of the function just because of the which path information being determined by some strange mechanism.

    The break of the wave function is not a bottom up approach. The photon does not act like a little machine, where when you know the mechanism, you can say that this or that will happen, and know all possible outcomes.
    It broke out of nowhere, and we had to find a theory which fits why it breaks, and it seems QMlers keep discovering new strangeness.
    It's like something a-causal happened. The path of the photon not being determined by a causal chain of basic forces acting on it, but a mere which path knowledge which determines it.
    It almost denies physics a bottom up approach, but allows for new strangeness of similar quality to be discovered along the path.

    It will take a genius to combine those two theories properly. One who can determine how relevant this strangeness is regarding the two postulates, and then derive IF necessary some more accurate formulas of SR by adjusting the two postulates to contain this strangeness of QM.
    However, there is no doubt that SR is on the right path as it has been confirmed experimentally many times.

    It is also a beautiful exercise in learning to not always trust your intuition, but get rid of it, and see what happens if you strictly follow two postulates with a clear mind.
    Einstein did just that.
    His main achievement to me is not relativity itself as great as it might be, but his tremendous impact on how physicists approach a problem in physics now.

    While intuition is our strongest weapon still, sometimes you have to throw some ideas resulting of it overboard when they just do not go in accord with observation.
    Build basic postulates based on observation and logic, and be persistent, using maths and geometry to get results. Then check your results experimentally.

    It also shows how useful maths/geometry as a tool is for physicists. They help a lot in ignoring intuition when needed, and simply get to results based on basic postulates you set.
     
    Last edited: Oct 25, 2012
  17. Oct 25, 2012 #16

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2016 Award

    Since the OP has decided to not participate/explain further in the thread that he/she started, and since the starting premise of this thread is false, this thread is now done.

    Zz.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Is existing relativity 100% correct, or are we waiting for something better?
Loading...