Do physicists need the idea of 'cause' or 'causation' to do physics?   Does it appear in physics, either in theory, answered , or in experiment? In a way analogous to how names and mathematics do.  If not, then it seems like a folk concept which exists only to help us learn physics or be inspired by it.
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I was reading  by Pedro Domingos and towards the end of the paper he makes this statement:  "Many researchers believe that causality is only a convenient fiction. For example, there is no notion of causality in physical laws. Whether or not causality really exists is a deep philosophical question with no definitive answer in sight..."  I was surprised by this statement because apart from Heisenberg's uncertainty principle, everything else (that I know of) in physics seems to operate under the assumption of . If you have an equation that describes a definitive outcome as the result of some input factors, then it is describing a causal relationship, is it not?
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I've always hit two big stumbling blocks in conceiving of the proof or disproof of  as being even valid idea, let alone an answerable question... I feel I must be misunderstanding some very fundamental things.   Quantum mechanics is deterministic, ignoring the bit where we take our complex number and fudge it into a probability. We use computers to make calculations to provide the predictions of quantum mechanics - how is this not itself a hidden variable theory?   From what I understand the famous Bell theorem and work around it doesn't disprove hidden variable theories, just one specific flavour of them, and even then I am not convinced. I feel like I must be missing something again, because this result seems to me in no way profound... although it certainly fits into the picture of the EPR 'paradox' and is a good demonstration of the validity of QM.  I guess the crux of my problem is that this 'area' really addresses wave function collapse and the problems it causes, but I don't see the need for some collapse mechanism to begin with... again I feel like I am missing something really fundamental.  Apologies if this is a bad question. I have had a look around and there are similar questions, but I don't feel that either of my points are addressed...
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There was a reason why I constantly failed physics at school and university, and that reason was, apart from the fact I was immensely lazy, that I mentally refused to &quot;believe&quot; more advanced stuff until I understand the fundamentals (which I, eventually, never did). As such, one of the most fundamental things in physics that I still don't understand (a year after dropping out from the university) is the concept of . No one cared to explain what a field actually is, they just used to throw in a bunch of formulas and everyone was content. The school textbook definition for a field (electromagnetic in this particular case, but they were similar), as I remember it, goes like:  An electromagnetic field is a special kind of substance by which charged moving particles or physical bodies with a magnetic moment interact.  A special kind of substance, are they for real? This sounds like the authors themselves didn't quite understand what a field is so they decided to throw in a bunch of buzzwords to make it sounds right. I'm fine with the second half but a special kind of substance really bugs me, so I'd like to focus on that. Is a field material? Apparently, it isn't. It doesn't consist of particles like my laptop or even the light. If it isn't material, is it real or is it just a concept that helps to explain our observations? While this is prone to speculations, I think we can agree that in scope of this discussion particles actually do exist and laws of physics don't (the latter are nothing but human ideas so I suspect Universe doesn't &quot;know&quot; a thing about them, at least if we're talking raw matter and don't take it on metalevel where human knowledge, being a part of the Universe, makes the Universe contain laws of physics). Any laws are only a product of human thinking while the stars are likely to exist without us homo sapiens messing around. Or am I wrong here too? I hope you already see why I hate physics. Is a field not material but still real? Can something &quot;not touchable&quot; by definition be considered part of our Universe by physicists? I used to imagine that a &quot;snapshot&quot; of our Universe in time would contain information about each particle and its position, and this would've been enough to &quot;de&quot; it but I guess my programmer metaphors are largely off the track. (Oh, and I know that the uncertainty principle makes such (de)serialization impossible — I only mean that I thought the Universe can be &quot;defined&quot; as the set of all material objects in it). Is such assumption false? At this point, if fields indeed are not material but are part of the Universe, I don't really see how they are different from  except for perhaps a more geeky flavor. When I talked about this with the teacher who helped me to prepare for the exams (which I did pass, by the way, it was before I dropped out), she said to me that, if I wanted hardcore definitions,  a field is a function that returns a value for a point in space.  Now this finally makes a hell lot of sense to me but I still don't understand how mathematical functions can be a part of the Universe and shape the reality.
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The question of whether or not a tree that falls in the forest makes a sound - if there is nothing or no one around to hear it - comes up frequently at my house.  So, my question is: is there any way to "prove" or "dis-prove" this using physics? If it can be proven what is the answer?  My idea is yes, of course it makes a sound even if there is nothing to sense it! However, my parents seem to think that if there is nothing to "take in" the sound waves, there is no sounds.
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It is well known that quantum mechanics and (general) relativity do not fit well. I am wondering whether it is possible to make a list of contradictions or problems between them?  E.g. relativity theory uses a space-time continuum, while quantum theory uses discrete states.  I am not merely looking for a solution or rebuttal of such opposites, more for a survey of the field out of interest.
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What I am interested to see are specific examples/reasons why gravity should be quantized. Something more than "well, everything else is, so why not gravity too". For example, isn't it possible that a quantum field theory on curved space-time would be the way treat QFT and gravity in questions where the effects of neither can be ignored?
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Possible Duplicate:          I've heard of De Broglie–Bohm theory a.k.a causal interpretation of quantum theory. The predictions match accurately with with the nondeterministic quantum theory.  As a philosophy buff this one seems just like the classical universe. No funny new-age religion style gimmicks.  So why don't people use this interpretation instead of the Copenhagen "magic" interpretation?  P.S. I'm not an expert. I possess only superficial knowledge of quantum physics.
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What is the meaning of ? I'm little confused about the word as there are some terms like moment of momentum, moment of mass, moment of force, etc. I want to know what exactly is meant by the word "moment".
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On the question of the  (i.e. that reality is a simulation), a friend of mine once remarked he didn't accept it on the grounds of . To me (with my admittedly instrumentalist view of science) this seems a misuse of Ockham's razor in that all my friend is really claiming is that it isn't empirically necessary (and hence outside of science).  Is the simulation hypothesis outside of science? If so, then does it pose a problem for scientific realism? If not, is it falsifiable? Is it an empirical question?
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Nonphysical entities cannot be observed. Therefore such entities cannot be verified by observation. How could statements like "God exists" be even considered true? Why would anyone appeal to the metaphysical realm at all?  It seems to me that the best method by which we should go about in understanding the world is by initially ruling out the possibility of the metaphysical altogether for the simplest answer (a sort of null hypothesis). Once we can get a hold of a natural cause of some phenomenon, we should be satisfied that that is all there is to it. Formulating some nonphysical cause would be unnecessary, superfluously complicated, or even cluttered. Now if there was some problem that we were certain could not be solved by observation or experimentation or whose solution could not possibly exist in the observable realm, yet must be true, I would consider the possibility of a metaphysical cause.      That said, I don't think that if you can't empirically observe something, it doesn't exist; rather, I would declare total agnosticism and say that it is unknowable.
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We all know this magical mathematical constant.   My question being , how and why pi just shows up in every other physics derivation or formula or even statistics for that matter .    Is it just coincidence or some actual reason?
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Sometimes people fail at asking a question by being too broad, unclear like . So I'll take a stab at what I believe to be the same question, but more concise and clearly stated:     Does infinity exist in either terms of structure, parameters, or   measurement in any physical systems?   Can infinity have any real connection with reality?  Or is infinity purely a mathematical concept just used by physicists as a convenient way to describe the very large, an approximation?  I have heard that if you model a physical system (), and you run into infinity as a solution, then you have either made an error in your calculations or your model is wrong.
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We typically say that forces cause acceleration inversely proportionate to mass. Would it be any less correct to say that acceleration causes forces proportionate to mass? Why?  (Note that the underlying question in my mind - essentially, what distinguishes cause from effect - is far more general. But this seems like a good place to start.)
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Possible Duplicate:          We carefully observe things, observe patterns and then build theories that predict.   String theory is frequently criticized for not providing quantitative experimental prediction.   What are the problems that prevent this theory from producing quantitative experimental predictions?   Is there no experiment suggested by string theorists to verify validity of their theory?  Is the problem mathematical? (or it just requires many dimensional equipments...just kidding).  I am not criticizing the theory because to do that I should understand it first, but I haven't studied it. I just want to know.
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Based on the problem of induction, nobody can assert with absolute certainty that the laws of science (i.e. physics, chemistry, etc,...) will hold all the time, in every part of the universe. Believing that that is the case is therefore a form of faith, not knowledge.  Current scientific consensus is that the universe doesn't stretch back indefinitely into the past, but came into existence a finite time ago with the big bang. The occurrence of the big bang and the subsequent evolution of the universe are both driven by the laws of physics. The laws of physics, seen this way, are the first cause of the universe and the higher power that governs it's day to day functioning.    So belief in science requires having faith, and belief in a first cause/higher power, two of the main components of theistic belief. And the laws of science then become some sort impersonal deity, akin to the deity of Deism. One could even envision a science based moral code based on neurological and environmental considerations, and we would then have all the constituents of  traditional religion: Faith, first cause, and a set of ethical laws.   Obviously, this theism is very different than the theism of the Abrahamic religions, especially since the god in question is not personal. But the way I see it, isn't it still a form of theism, with the laws of science/physics as its deity?
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Why is dark matter the best theory to explain the missing mass problem?    Why is dark matter mathematically necessary to explain the missing mass problem?    On a side not I believe dark matter is definately intuitive the next logical step in physics is to accept the fact the direct observations can not always be the determining factor in the acceptance of a theory.  Positivism is not going to be the only driving force in physics forevermore.    One theory that seems almost as good is the supersymmetric particle. What determination which are actually detectible and how would we distinguish the differences between the two?    References:   .
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A theory among scientists says that quantum fluctuations caused the big bang and created the universe. This seems plausible to me.   What I can't grasp yet is how a quantum fluctuation can even start without an existing universe. Aren't all physical laws created with the universe? I understand that there is no notion of "before" with respect to time, however the big bang is theorised to have occurred, but for that to occur there must have first existed something right?  I wonder also, if there was a more nothingness instead of vacuum before the universe existed and how a quantum fluctuation could have started really from ex nihilo instead of a vacuum.