Are physics in the particles, or reality itself?

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Are physics in the particles, or reality itself?

Postby King Author » Sat Jan 11, 2014 2:44 pm UTC

Are the laws of physics the way they are because of the specific particles in which they're expressed, or are the laws of physics part of reality itself?

Like, is the spin of an electron what it is because it just so happens to be that, that's just the way the particle turned out, or must it be that, is the law for the spin of an electron somehow endemic to reality?

Put another way, if, a zonktillion years after the heat death of our universe, another big bang occured, would the laws of physics be the same? Or might they be utterly different if the fundamental particles generated by that bang are different than ours?
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Re: Are physics in the particles, or reality itself?

Postby Aiwendil » Sat Jan 11, 2014 5:16 pm UTC

I'm going to get ever so slightly philosophical and point out that it's not necessarily the case that there is a meaningful difference between 'the laws of physics are the way they are because of the specific particles in which they're expressed' and 'the laws of physics are part of reality itself'. If one is of a positivist inclination (as I am), then one tends to read those statements as differing only in a 'metaphysical' sense, and hence a meaningless one.

In other words, the universe we observe is the universe we observe. The laws of physics are 'just' useful generalizations about those observations.

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Re: Are physics in the particles, or reality itself?

Postby infernovia » Sat Jan 11, 2014 5:36 pm UTC

Are you asking the patterns we observe could potentially apply to all universes that followed a big bang?

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Re: Are physics in the particles, or reality itself?

Postby Tchebu » Sun Jan 12, 2014 8:29 am UTC

If we start with a certain set of not-too-crazy assumptions (locality, lorentz invariance etc), there are quite heavy constraints on the "way things can possibly be", but they are not fully constraining.

Specifically, the particle content of the standard model (or at least certain parts of it) is more or less necessary to avoid some very bad things (quantum anomalies, landau poles, etc), but the relative strengths of the various interactions in it are not fully constrained by any underlying principle. So in that sense, the spin of the electron is the way it is because that's what it means to be an electron, and electrons are required in the standard model, but things like it's charge-to-mass ratio has no underlying explanation that we're aware of...
Our universe is most certainly unique... it's the only one that string theory doesn't describe.

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Re: Are physics in the particles, or reality itself?

Postby Tub » Mon Jan 13, 2014 12:39 pm UTC

Tchebu wrote:If we start with a certain set of not-too-crazy assumptions (locality, lorentz invariance etc), there are quite heavy constraints on the "way things can possibly be", but they are not fully constraining.

Given just your not-too-crazy assumptions, and ignoring any other observations about the universe we live in, can you really make and meaningful constraints on the "way things can possibly be"?

How many dimensions does our universe possess? Do you necessarily arrive at 3 spatial, 1 time and x rolled up dimensions?

We also have an amount of fields that permeate our universe. Which of those can be derived from your assumptions? Would a universe be possible that's identical to ours, but is missing the Higgs field, or the electromagnetic field? Instead having an entirely different field with a force unlike any in our universe? It certainly wouldn't be a healthy environment for humans, but would such a universe contradict any of your basic assumptions?

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Re: Are physics in the particles, or reality itself?

Postby Tchebu » Mon Jan 13, 2014 6:44 pm UTC

How many dimensions does our universe possess? Do you necessarily arrive at 3 spatial, 1 time and x rolled up dimensions?


Quantum Field Theory has no constraints on the dimensionality of spacetime, which makes sense since it doesn't deal with gravity, so spacetime is just a background for it. I believe more than 1 time dimension gets you in all sorts of trouble though, so 1 time dimension. If you want to hope to unite gravity with the other forces and not have it forever sit as a separate thing, then supersymmetry is pretty much necessary, in which case there's a limit on the number of dimensions allowed, which is 11. String theory certainly derives the dimensionality of space in a very strict way. None of this is verified obviously, but I'm just pointing out that there can be constraints even here, but the precise answer would have to come from quantum gravity...

We also have an amount of fields that permeate our universe. Which of those can be derived from your assumptions? Would a universe be possible that's identical to ours, but is missing the Higgs field, or the electromagnetic field? Instead having an entirely different field with a force unlike any in our universe? It certainly wouldn't be a healthy environment for humans, but would such a universe contradict any of your basic assumptions?


This part actually is quite heavily constrained, but again, not fully. Lorentz invariance requires that your fields transform correctly under Lorentz transformations and rotations. This narrows down our options to scalar fields, spinor fields (fermions), vector fields, fields of spin 3/2, 2 etc.

The other major constraints come from renormalizability. The coupling constants in your theory, which govern the strengths of interaction between the fields, change depending on the energy scale of the processes you're looking at. This happens because quantum processes contribute more to things like particle scattering at higher energy. Basically, at high energy you can make more virtual particles, which introduce deviations from the same process happening at low energy. Since we want to have a "fundamental" theory, it needs to first and foremost make sense at high energy, with the low energy behavior as a consequence. This allows us to immediately reject any interactions whose strength becomes infinite at some high but finite energy. In particular this includes any interactions involving spins greater than 1, so as far as field content we're stuck with scalars, fermions and vector fields.

Furthermore, certain kinds of interaction allow you to have configurations of particles with arbitrarily negative energy. Such a theory is completely unstable, since everything would just decay indefinitely trying to reach the bottom of the bottomless energy pit. This means we have to get the strength of these interactions to zero. However, once again due to quantum corrections, setting them to zero at one energy scale doesn't guarantee that they'll stay that way at all energy scales! The only way to make sure they stay zero at all energy scales is to introduce gauge symmetry, which recruits our vector fields to become the force-carrying particles we know and love and specifies exactly the form of their interactions with the fermions.

The simplest kind of gauge symmetry automatically spits out electromagnetism! However, once again, pure electromagnetism runs into some nasty divergences at large energy scales, so we need to consider a bigger symmetry group than that. This smallest such group gives electroweak theory. This answers your question about whether you can remove the electromagnetic interaction. The answer is "no" because that would severely mess up the weak interaction, so you'd have to remove them together!

Once you have this gauge symmetry, some quantum processes can violate it. Such processes are called quantum anomalies and they need to cancel out. The standard model has this anomaly cancellation feature, but part of the cancellation involves quarks and involves the fact that they have 3 color charges. This means that we need to have the strong nuclear interaction in the mix as well! I'm not sure if it's the only way to achieve anomaly cancellation, but if there are other ways they're definitely not obtained by slight deformations of the standard model. If there are no other ways to cancel the anomalies, then the standard model is actually the smallest model with interactions, whose particles transform properly under Lorentz transformations, that make sense at high energies and doesn't collapse into a negative energy abyss...

You can in principle have larger gauge groups without any immediately obvious problems, but the examples so far are a good reason to be cautious about just slapping new interactions on top of everything. You definitely have to check for renormalizability and anomaly cancellation every time you throw in a new ingredient.
Each new gauge group comes with its own coupling constant, which is independent of the rest, so that's the part that's not constrained (however their dependence on energy scale definitely depends on the other interactions).

So the bottom line is that the types of particles we can have are constrained, the form of the interactions is somewhat constrained but not entirely, and the relative strengths of the interactions are not constrained at all... I don't know if these match your definition of "meaningful constraints".
Our universe is most certainly unique... it's the only one that string theory doesn't describe.

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Re: Are physics in the particles, or reality itself?

Postby Tub » Tue Jan 14, 2014 11:07 am UTC

Thanks for the detailed writeup.

Tchebu wrote:I believe more than 1 time dimension gets you in all sorts of trouble though, so 1 time dimension.

Any sort of trouble in particular?

According to
http://en.wikipedia.org/wiki/Multiple_time_dimensions
it seems like such possibilities have been researched and the formulas check out.

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Re: Are physics in the particles, or reality itself?

Postby Tchebu » Tue Jan 14, 2014 4:30 pm UTC

Causality and locality is quite difficult to implement. For example on the picture in the wiki link, the causal region is actually the outside of a cone now, so I can loop around it all while remaining on a timelike curve and end up back where I started or, even worse, inside the cone. This means that events can influence other simultaneous events, which is pretty much the definition of non-locality. This seems to agree with the sentence from the wiki page

Weinstein proved the existence of a well-posed initial value problem for the ultrahyperbolic equation (wave equation in more than one time dimension).[4] This showed that initial data on a mixed (spacelike and timeline) hypersurface obeying a particular nonlocal constraint evolves deterministically in the remaining time dimension.

So not only is your initial data non-local, it has to also be specified on a partially timelike surface and then you can "predict" what happens along the remaining time direction...

I suppose this is only an argument against large extra time dimensions. If you compactify the extra dimension you can put a limit on the extent to which you violate locality and that might be good enough.
Our universe is most certainly unique... it's the only one that string theory doesn't describe.

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Re: Are physics in the particles, or reality itself?

Postby eSOANEM » Wed Jan 15, 2014 11:04 am UTC

Tub wrote:According to
http://en.wikipedia.org/wiki/Multiple_time_dimensions
it seems like such possibilities have been researched and the formulas check out.


The see-all on that page links to another article called "privileged character of 3+1 spacetime" which ought to tell you that there are issues with other signatures :p

Anyway, there's this diagram which gives the relevant information:

Image

IIRC when it says "unpredictable" it means the differential equations can only be solved numerically. For 1 temporal dimension, stable orbits and EM are only possible in 3 spatial dimensions.
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Re: Are physics in the particles, or reality itself?

Postby doogly » Wed Jan 15, 2014 6:16 pm UTC

Unpredictable doesn't mean numerical only, it means for given initial data on a spacelike surface you do not have a unique solution. Uniqueness of solutions always seemed like a super obnoxious and picayune thing for the math folks to care about when I took differential equations (and in research I came across a paper where they prove uniqueness but *not* existence, guaranteeing either 0 or 1 solution... so useful...), but it is a big deal.
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Re: Are physics in the particles, or reality itself?

Postby thoughtfully » Wed Jan 15, 2014 6:19 pm UTC

Yeah, you gotta love those math guys. They come up with the strangest, crazy-bonkers useless stuff, like Group Theory and Topology. Bunch of nutters!
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Re: Are physics in the particles, or reality itself?

Postby eSOANEM » Wed Jan 15, 2014 8:46 pm UTC

doogly wrote:Unpredictable doesn't mean numerical only, it means for given initial data on a spacelike surface you do not have a unique solution. Uniqueness of solutions always seemed like a super obnoxious and picayune thing for the math folks to care about when I took differential equations (and in research I came across a paper where they prove uniqueness but *not* existence, guaranteeing either 0 or 1 solution... so useful...), but it is a big deal.


Huh. That's even worse than I thought it was. Thanks for clearing that up :)
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Re: Are physics in the particles, or reality itself?

Postby King Author » Sat Jan 18, 2014 6:31 am UTC

Thanks for the replies thus far, fellas.

Aiwendil wrote:I'm going to get ever so slightly philosophical and point out that it's not necessarily the case that there is a meaningful difference between 'the laws of physics are the way they are because of the specific particles in which they're expressed' and 'the laws of physics are part of reality itself'. If one is of a positivist inclination (as I am), then one tends to read those statements as differing only in a 'metaphysical' sense, and hence a meaningless one.

In other words, the universe we observe is the universe we observe. The laws of physics are 'just' useful generalizations about those observations.


Agreed. My question still stands, though :p

infernovia wrote:Are you asking the patterns we observe could potentially apply to all universes that followed a big bang?


Nay. I mean like, do particles behave the way they do 'cause of their interactions with other particles (i.e., the laws of physics are the way they are because of the stuff that makes up the universe), or to use a programming metaphor, because the programming environment that is reality only allows them to behave that way.

Obviously we could imagine a universe which is utterly different than ours because it has different types of particles, and obviously if you changed the way particles behave in our universe, it'd radically change things (maybe stars would've never formed and we wouldn't be here).
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Re: Are physics in the particles, or reality itself?

Postby PM 2Ring » Sat Jan 18, 2014 7:24 am UTC

In quantum field theory (QFT), particles aren't the fundamental entities of physical reality - they are "merely" excited states of the underlying field. In a sense, particles are a convenient fiction that make it easier to conceptualize & calculate how the various quantum fields behave & interact.

The quantum fields have various symmetries associated with them; particle properties are basically manifestations of these underlying symmetries. As Tchebu mentioned, some of these symmetries seem to be necessary, in that it's hard to make a physically sane system that doesn't have these symmetries.

Note: I am not a Real Physicist™; hopefully Tchebu & Doogly can expand on and correct what I've said above. :)

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Re: Are physics in the particles, or reality itself?

Postby doogly » Sat Jan 18, 2014 3:13 pm UTC

Yeah, the laws of physics are things like the standard model lagrangian, and it tells you what the particles all have to be like.

The original question just seems sort of nonsense. I can't imagine, even with my very best imaginings, what the real difference between those two descriptions would be.

Maybe this is like asking, are the laws of physics a necessary or a contingent truth? Like we are doing some intellectual archaeology, and thinking like a medieval scholastic.
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Re: Are physics in the particles, or reality itself?

Postby Sizik » Sat Jan 18, 2014 6:41 pm UTC

I suppose a better way to form the question would be: If you took some particles from our universe and "imported" them into a different universe with a completely different set of laws, would our particles act the same way as in our universe, or would their behavior change due to the new laws of physics?

A somewhat related question would be: Would the electromagnetic field be detectable/still exist if we got rid of all photons and charged particles?
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Re: Are physics in the particles, or reality itself?

Postby Nicias » Sat Jan 18, 2014 6:58 pm UTC

Sizik wrote:A somewhat related question would be: Would the electromagnetic field be detectable/still exist if we got rid of all photons and charged particles?


Photons are excited states of the electromagnetic field. Particles don't exist separate from the fields.

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Re: Are physics in the particles, or reality itself?

Postby doogly » Sat Jan 18, 2014 8:26 pm UTC

Sizik wrote:I suppose a better way to form the question would be: If you took some particles from our universe and "imported" them into a different universe with a completely different set of laws, would our particles act the same way as in our universe, or would their behavior change due to the new laws of physics?

This is just nonsense though, is the problem with such a question.
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Re: Are physics in the particles, or reality itself?

Postby fishfry » Sat Jan 18, 2014 11:32 pm UTC

King Author wrote:Are the laws of physics the way they are because of the specific particles in which they're expressed, or are the laws of physics part of reality itself?


Maybe the laws of physics are only in the experiments. They tell us something about the human mind and nothing at all about external reality, whatever that is. This is a question of philosophy.

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Re: Are physics in the particles, or reality itself?

Postby thoughtfully » Sun Jan 19, 2014 1:49 am UTC

The models we build are without question contrivances of our minds. If there is some reality "out there", it's unknowable in the sense that our models will always be provisional. We can't say that some future observation can't come along and force a revision. This is simply the nature of inductive reasoning.
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Re: Are physics in the particles, or reality itself?

Postby untitled » Fri Jan 31, 2014 2:57 pm UTC

Regarding experiments to models (and models to experiments), is it possible to conceive any measuring device which the human mind cannot imagine?

I would assume yes, based on random numbers. Devices for measuring randomness (or gathering random numbers) are, of course, a product of human imagination - but the results themselves (e.g. the decay of radioactive material) are not. Thus, even by an infinitesimally small margin, these measurements are less anthropocentric than the device we made. Could these results aid us in producing a less anthropocentric measuring device than the first one? In other words, could random numbers lead to the conceptualization of a measurement device which we could have not "imagined" by ourselves? If yes, this device would yield even more "removed-from-human-perspective" results than the previous set of random numbers. Of course, this whole line of thinking may be flawed in more ways than one: for example the resulting measuring devices, instead of being anthropocentric, will be "radioactivedecay-o-centric" (defeating our purpose of developing something nothing-o-centric). This, apart from the question "can we measure something which we can't experience in any way?" leads to the question "do radioactive elements have free will?"

Of course, humans will always find some neat description for any/every phenomenon - and this is because humans are the best, by definition! :mrgreen: If they weren't, we would be in big trouble. Still, it's funny to think about WHERE these new phenomena "come from."

I am quite sure that the development of measurement devices started with phenomena which seemed far more random at that time than it is today, for example p(animal dies | animal is poked with a stick) leads to p( p(animal dies | animal is poked with a stick) | sharpness of the stick) and the necessary measurement device for the sharpness of a stick. This is a primitive example but at least it's more valid (more Mach-ian, I would hazard to presume) than the anthropocentric view of "telescopes are just biiiiiig eyes." The freaky question is: "where does it lead?"

Von Neumann said that "In mathematics you don't understand things. You just get used to them."; it would be awesome if somebody could find/say a comparable aphorism for physics (joke: "in physics you don't get used to things, you just understand them")

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Re: Are physics in the particles, or reality itself?

Postby thoughtfully » Fri Jan 31, 2014 3:44 pm UTC

I'm not sure what it means to concieve of something unimaginable. How are they not synonyms in this context?

Also, one cannot "measure" randomness. One measures voltage, or temperature, etc. If the process under scrutiny has stochastic behavior (a property of the model), then fine, but that isn't the same.

Measurement will always be a lossy operation, but that isn't what you seem to be getting at. But it's hard to see what you're trying to get at.
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Re: Are physics in the particles, or reality itself?

Postby untitled » Fri Jan 31, 2014 5:00 pm UTC

No, the synonym is to conceive something UNIMAGINED, not UNIMAGINABLE. Maybe my usage of the word "conceive" wasn't the most fortunate.

For example,
Conceive (build, execute) a measuring device at time t=0 and explain (predict) it's measurements at time t1>t0.
versus
Explain (predict) some measurement at time t=0 and then conceive (build, execute) a measuring device for it at time t1>t0.

Of course, the measuring device can also be represented by your mind and your senses - which by itself makes the case of "predict before the conception" impossible... basically, a measurement of your senses doesn't reach your consciousness unless it's "calculated beforehand"... otherwise we could tell the state of each of our neurons just by thinking about them. Unless you can use something else than your mind (and something else than the things that could be conceived by your mind - imaginable things, even if unimagined yet), you cannot really predict something before having the measuring device for that prediction... you cannot google after stuff you never heard of (unless you randomly bang your keyboard... which is kind of my point about randomness).

Yes, mathematics comes close to this (I believe that because our neurons also "know" mathematics, so there is a continuity between "the world" and "what we perceive") - but this topic is specifically about physics!!

So, to solve this dilemma and expand the world of possible measuring devices, we would need something other than your brain (or human brain, we want to get rid of anthropocentricity - which was one of the points in this topic - which is why I am typing all these letters!) to make predictions, predictions made before we use our head to build a measuring device. In my previous post, I explained why randomness* would be feasible.

If I'm correct, we are already using this system to make predictions about fundamental constants (we can explain where they come from but we can't make a device to measure them directly... yet) and predict stuff about black holes with the help of mathematics - and no measuring devices whatsoever (discovery by telescopes came after the prediction; hmm, this reminds me of gravitational lensing which was also predicted before being measured)... If we could formalize the procedure, maybe we could build technology which, for example, could translate the tachyon world (N=1, T=3) into visible spectrum images (N=2, T=0)... or explore worlds with other laws of physics than ours... maybe even travel there... wouldn't that be neat?

I hope I am making more sense and you can tell me if:
1. I am a moron and need to shut up. (I am suspecting this is the case :mrgreen: )
2. I am a genius and need to shut up.
3. I need to read book XYZ and then tell us again the whole story.

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*A phenomenon is random if it's measurable but, by definition, you can't explain (predict) it. E.g. if voltage is 5V at t=0, based on this (and any previous measurements t<0) you cannot predict the voltage at t=1... although sometime in the future maybe you will be able to! Obviously, trial-and-error is also a form of taking advantage of randomness.

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Re: Are physics in the particles, or reality itself?

Postby thoughtfully » Fri Jan 31, 2014 5:52 pm UTC

I think all geniuses probably go through a stage of being a noisy moron early in their development :)

There's this misunderstanding about measurement again. We don't have any black hole detectors. We use light detectors (and other wavelengths), and hopefully soon, gravity wave detectors to observe them. Gravity waves were predicted before we had devices dedicated to their study, but Michaelson interferometers existed, which is basically what modern gravity wave detectors are. Light waves and gravity waves are information conveyed across the cosmos completely independently of its source. The bit of charge or mass oscillating at some frequency could be caused by all sorts of things, after all. We interpret this information based mainly on the direction it came from and how much energy it carried, occasionally using other bits like the phase.

The other stuff that falls from the sky we use to puzzle out the cosmos are matter particles (including neutrinos, I'm including all fermions among "matter particles"). The same goes for them, pretty much.

When some advance in theory predicts something new, it obviously has to have observable consequences, or it's meaningless. It's an exercise in deduction to use the theory to find out what changes are expected. There's going to be a change of momentum of something somewhere. If it's spooky and mysterious, it doesn't being in empirical studies.

Well, unless it involves Quantum Mechanics. No universe is perfect!
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Re: Are physics in the particles, or reality itself?

Postby untitled » Fri Jan 31, 2014 8:24 pm UTC

Yes, we are 100% in agreement as I have said that we cannot measure black holes directly - in fact people made predictions about their properties before they were observed by telescopes (if I am not mistaken... if I am, the example of gravitational lensing surely works: the theory was developed years before observing the effect by telescope). The observation of gravity waves is another great example and I can't wait for LISA to get started :D

What "bothers" me is that if the process of "we know what will fall out of the sky before we make a device that measures it" can be formalized. A bit resembling the halting problem in computing science - but in many dimensions not just one. Look:

The scientific method formalizes this way
1. propose theory; 2. make something which measures; 3. explain/predict observed measurements; 4. confirm theory.

I would like
1. propose theory; 2. explain/predict unobserved measurements; 3. make something which makes those measurements; 4. confirm theory.

I admit, it's more like alchemy than science... but fortunately it doesn't matter which interpretation of quantum theory is valid (Copenhagen, MultiWorlds or my personal favorite Pilot Wave), if it can work, it will work. Because we are humans and we are the best :mrgreen:

I hope it's clearer now from where the problem of "measuring-without-building-anything-not-even-in-your-head" comes :)

Thank you for motivating me to make it clearer.

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Re: Are physics in the particles, or reality itself?

Postby thoughtfully » Sat Feb 01, 2014 5:58 am UTC

The usual formulations don't include the construction of apparatus. Science works fine with no apparatus or only the existing stuff. Indeed, it's hard to see an epistemic distinction between observations mediated by artificial constructions plus our biological apparatus versus simply the biological apparatus.

I had a philosphy of science professor who used to (still does, I imagine) say that observations are theory laden. You can't escape it. Every bit of data gets an interpretation slapped on it, consciously or otherwise.

Anyway, the way things generally work is how you seem to want them to be. The prediction come before any new apparatus. Otherwise we wouldn't know how to build something that could test the predictions!

Maybe you are thinking backwards a step, to the observations that come before the inductive part where a theory is constructed to fit unexplained data. There's nothing peculiar about existing apparatus providing data that does not fit existing theories. This fits with the previous paragraph when the loop is joined. Science is a big feedback mechanism.

You may be inviting some to put you in the moron camp with your affinity for hidden variable interpretations (Pilot waves). These have been convincingly excluded by experiment. There are possible loopholes in the theory/interpretation, but most experts think they are longshots.
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Re: Are physics in the particles, or reality itself?

Postby untitled » Sat Feb 01, 2014 9:19 am UTC

Thank you very much for your answer - I am sure that as I read more about theory-laden-ness (and philosophy of science... I only got as far as Kuhn and the writings of Koestler - I don't even remember them anymore!) I will be able to formulate the (epistemological and methodological) conditions necessary for a new kind of measurement device more easily. I totally agree that science is a big feedback mechanism (there was a dude who said that science is the way the universe tries to understand itself :mrgreen: ) and I want it to be more, even if that "more" is something like "we discover things other than what we think we need... before we discover what we think we needed."

Also, your warning about hidden variable interpretations is well-known by me and - while I "believe" - I fully agree with Deutsch's statement: "pilot-wave theories are parallel-universe theories in a state of chronic denial."

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Re: Are physics in the particles, or reality itself?

Postby Bluewink » Mon Feb 17, 2014 5:42 pm UTC

About the OP. The problem with your question is that the particles are an expression the laws of physics and the laws of physics are the description of "reality". It's all one and the same.

In other universes, other "realities", there could be different laws which would give birth to different particles. But "our" particles could not exist in those different universes. (Well, from what I understand, we could have the "same" universe with different particle masses or electric charge, but when you get to more complex properties like spin, they are much more intrinsic to the definition of the particle and the definition of the law of physic that describes it.)


About untitled's question. You say this is what you want:
1. propose theory; 2. explain/predict unobserved measurements; 3. make something which makes those measurements; 4. confirm theory.


This is already how science works nowadays. Well, with many, many loops before getting to step 4.

But from your text, this is what I understand you would like:

1. Make something which can mesure something we haven't imagined yet; 2. Build theory that explains measurements; (3. Make more measurements to eventually confirm theory)

This has already happenend when scientists discovered that tools which had been developped for one field of study could be used in another. For instance when Volta discovered that "physical" electricity was the same as "biological" electricity. Nowadays, I doubt that such a happy accident can still happen. I certainly don't think that it can be formalized.

You also mention that you would like to take science away from anthropocentrism. Well, we measure radiation that we can't see or feel. We detect particles that pass right through us. Are there levels of abstraction we haven't reached yet? Most likely. But to me, where you want to take it is so far away from our senses that we wouldn't be able to tell that our device had made a measurement.

I actually think you have a much better chance of understanding things in mathematics than in physics! My version would be "In physics you don't understand things. You just describe them and get used to them."

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Re: Are physics in the particles, or reality itself?

Postby untitled » Thu Feb 20, 2014 8:45 am UTC

Bluewink wrote:1. Make something which can mesure something we haven't imagined yet; 2. Build theory that explains measurements; (3. Make more measurements to eventually confirm theory)

This has already happenend when scientists discovered that tools which had been developped for one field of study could be used in another. For instance when Volta discovered that "physical" electricity was the same as "biological" electricity. Nowadays, I doubt that such a happy accident can still happen. I certainly don't think that it can be formalized.

You also mention that you would like to take science away from anthropocentrism. Well, we measure radiation that we can't see or feel. We detect particles that pass right through us. Are there levels of abstraction we haven't reached yet? Most likely. But to me, where you want to take it is so far away from our senses that we wouldn't be able to tell that our device had made a measurement.


I thank you from the bottom of my heart for clarifying (to me, in the first place) what I wanted to say and offering all the necessary pointers. I am a big fan of interdisciplinary science but unfortunately suck at physics and sensor theory (if that field even exists).

I actually want to take away science from anthropocentrism in order to bring it's (to us, unimaginable) fruits back, namely to a proximity which at this moment enjoyed by our five senses. The thing is not to make abstractions but to "bring them home": we could only tell that the device is working if we "feel" it's ambiguous presence and other people benefiting from the device can also feel it (and may be able to learn to use it in similar ways - think about color vision and qualia).

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Re: Are physics in the particles, or reality itself?

Postby cemper93 » Wed Mar 05, 2014 9:31 am UTC

Because apparently everybody got nerd-sniped by a discussion I could not quite follow, I'd like to address the OP's question from a different angle.

In modern ontology (the philosophy of existence), there are two common ways of viewing the "being" of things, which your question relates to; these two viewpoints are the noumenal and the phenomenological.

Noumenal theories hold that things have some kind of inner essence. These types of theories have been around since antiquity. A popular example for ancient-day noumenology is Platon: according to his theory of forms, everything that exists exists as a "shadow" of some pure, perfect "idea" or "form" of that object, which cannot be perceived by us (and, according to him, is part of a different plane or something). By this argument, the behavior of particles would indeed be a part of their particle-essence - they would mimic the behavior of the perfect particle-form.
Another famous philosopher who developed a noumenal theory of ontology is Immanuel Kant. According to him, there are three - I guess you could call it layers of reality - that pertain to an object: "that which has been thought", "the thing itself" and the "thing on itself". Since "that which has been thought" is mostly an epistemelogical idea, what is interesting is the difference between the thing itself and the thing on itself: much like Platon, Kant asserts that things do have a layer that we can perceive (the thing itself - for example, you can knock on a chair and hear a knocking sound, or you can trap an electron in a floating gate and save a bit of information) as well as a layer that we can't (the thing on itself - the inner essence of the thing, that, which makes the chair a chair, the very chair-being of being a chair, also called the "noumenon"). Kant further elaborated that since we can only ever perceive the surface of a chair, but not its inner chair essence, trying to do the latter is futile, any ontological theory trying to do that is bound to fail, and Kant is the be-all end-all to all of philosophy because he's, like, wicked smart. Physics, hence, can be thought of as the inner essence of particles.

This snottiness may be a part of why "fuck Kant" has become a popular trope among all ontological theories that came after him. The most relevant theories of those are the phenomenological ones, as they have been developed by Husserl, Heidegger and Sartre. By these theories, there is no such thing as a layer behind reality: reality is what we perceive, and what we perceive, that is reality. The question "what makes a chair a chair?" does not really make sense if you try to answer it from that point of view: if you look at a chair, you see four legs, a seat and a back rest, and if you punch it, you hear a knocking sound and your knuckles hurt. That is obvious, but it is also all there is to say about what a chair is like. Likewise, electricity, for example, can be perceived by your lightbulb going on when you flip the switch, and by hurting a lot when you stick your finger into the outlet - but there is nothing behind these "phenomena" that is really some kind of true form, electricity is nothing but - as Sartre writes - the endless sequence of manifestations and the rule that holds them together. Even the very being of things is nothing but a phenomenon, the phenomenon of being: if it wasn't there, I couldn't perceive it, and hence, it would not exist. By these theories, particles do not only not have a perfect particle-essence: they do quite literally not exist, because they are nothing but the rule of the endless sequence of manifestations. Yes, of course you can use the idea of particles to explain a lot of phenomena: but this doesn't mean that these phenomena do actually point you towards the particles as their "true form of being", it simply means that you can use the particles as a reductionist approach to explain them. By this logic, physics is neither in the particles nor in reality itself: it is nothing but a rule.

Disclaimer: I'm not a professional philosopher and I don't usually read my philosophy books in English, so I've probably got the terms all wrong.

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Re: Are physics in the particles, or reality itself?

Postby doogly » Wed Mar 05, 2014 12:34 pm UTC

Seriously though, fuck Kant.
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Re: Are physics in the particles, or reality itself?

Postby thoughtfully » Wed Mar 05, 2014 1:51 pm UTC

cemper93 wrote:Physics, hence, can be thought of as the inner essence of particles.

This only holds for some "inner essense" physics. The physics we know is based on measurements and some mathematical fiddling around. It is mercurial (because measuring always introduces imprecision), and hence not fundamental or "essential".
doogly wrote:Seriously though, fuck Kant.

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Re: Are physics in the particles, or reality itself?

Postby Xanthir » Wed Mar 05, 2014 7:06 pm UTC

cemper93 wrote:Disclaimer: I'm not a professional philosopher and I don't usually read my philosophy books in English, so I've probably got the terms all wrong.

Only two that I noticed: the guy's name is "Plato", not "Platon", and the Kant's third form is "the thing in itself", not "the thing on itself".
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Re: Are physics in the particles, or reality itself?

Postby gmalivuk » Wed Mar 05, 2014 11:30 pm UTC

Also, it's "epistemological", not "epistemelogical".

But the nice thing about European philosophical terms is that most of them made their way into most European languages relatively unchanged, so apart from these sorts of minor spelling issues, it can often be easier to communicate in a second language about high-brow philosophical issues than about what you want to get at the grocery store.

Completely off-topic:
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Re: Are physics in the particles, or reality itself?

Postby cemper93 » Thu Mar 06, 2014 12:49 am UTC

thoughtfully wrote:This only holds for some "inner essense" physics. The physics we know is based on measurements and some mathematical fiddling around. It is mercurial (because measuring always introduces imprecision), and hence not fundamental or "essential".

I was talking about physics as in "metaphysics", not as in "physical science". Or to be more precise, I was talking about what physics means in both words - it has just become an annoying convention to call the science that studies physics the same name as the object of it's study :D

Xanthir wrote:Only two that I noticed: the guy's name is "Plato", not "Platon", and the Kant's third form is "the thing in itself", not "the thing on itself".

Thanks, though both I find very weird. Platon is clearly the correct name, and "thing in itself" is an odd translation at least, since "in" is definitely a mistranslation for the German preposition "an" (as in "Ding an sich"). I guess to be totally fair, I'd have to admit that "on" keeps less of what Kant wanted to convey with the term, but whoever translated that originally should really just have gone with "thing by itself", or even "thing per se", which is the term that Kant tried to pitifully translate into German in the first place.

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Re: Are physics in the particles, or reality itself?

Postby Quizatzhaderac » Fri Mar 28, 2014 9:20 pm UTC

The thing about recursion problems is that they tend to contain other recursion problems.

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Re: Are physics in the particles, or reality itself?

Postby quarkcosh1 » Thu Apr 03, 2014 8:01 pm UTC

eSOANEM wrote:
Tub wrote:According to
http://en.wikipedia.org/wiki/Multiple_time_dimensions
it seems like such possibilities have been researched and the formulas check out.


The see-all on that page links to another article called "privileged character of 3+1 spacetime" which ought to tell you that there are issues with other signatures :p

Anyway, there's this diagram which gives the relevant information:

Image

IIRC when it says "unpredictable" it means the differential equations can only be solved numerically. For 1 temporal dimension, stable orbits and EM are only possible in 3 spatial dimensions.


What exactly do they mean by too simple? Also do those unpredictable universes have no laws of physics? How unpredictable would they be?

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Re: Are physics in the particles, or reality itself?

Postby quarkcosh1 » Thu Apr 03, 2014 8:27 pm UTC

Tchebu wrote:
How many dimensions does our universe possess? Do you necessarily arrive at 3 spatial, 1 time and x rolled up dimensions?


Quantum Field Theory has no constraints on the dimensionality of spacetime, which makes sense since it doesn't deal with gravity, so spacetime is just a background for it. I believe more than 1 time dimension gets you in all sorts of trouble though, so 1 time dimension. If you want to hope to unite gravity with the other forces and not have it forever sit as a separate thing, then supersymmetry is pretty much necessary, in which case there's a limit on the number of dimensions allowed, which is 11. String theory certainly derives the dimensionality of space in a very strict way. None of this is verified obviously, but I'm just pointing out that there can be constraints even here, but the precise answer would have to come from quantum gravity...

We also have an amount of fields that permeate our universe. Which of those can be derived from your assumptions? Would a universe be possible that's identical to ours, but is missing the Higgs field, or the electromagnetic field? Instead having an entirely different field with a force unlike any in our universe? It certainly wouldn't be a healthy environment for humans, but would such a universe contradict any of your basic assumptions?


This part actually is quite heavily constrained, but again, not fully. Lorentz invariance requires that your fields transform correctly under Lorentz transformations and rotations. This narrows down our options to scalar fields, spinor fields (fermions), vector fields, fields of spin 3/2, 2 etc.

The other major constraints come from renormalizability. The coupling constants in your theory, which govern the strengths of interaction between the fields, change depending on the energy scale of the processes you're looking at. This happens because quantum processes contribute more to things like particle scattering at higher energy. Basically, at high energy you can make more virtual particles, which introduce deviations from the same process happening at low energy. Since we want to have a "fundamental" theory, it needs to first and foremost make sense at high energy, with the low energy behavior as a consequence. This allows us to immediately reject any interactions whose strength becomes infinite at some high but finite energy. In particular this includes any interactions involving spins greater than 1, so as far as field content we're stuck with scalars, fermions and vector fields.

Furthermore, certain kinds of interaction allow you to have configurations of particles with arbitrarily negative energy. Such a theory is completely unstable, since everything would just decay indefinitely trying to reach the bottom of the bottomless energy pit. This means we have to get the strength of these interactions to zero. However, once again due to quantum corrections, setting them to zero at one energy scale doesn't guarantee that they'll stay that way at all energy scales! The only way to make sure they stay zero at all energy scales is to introduce gauge symmetry, which recruits our vector fields to become the force-carrying particles we know and love and specifies exactly the form of their interactions with the fermions.

The simplest kind of gauge symmetry automatically spits out electromagnetism! However, once again, pure electromagnetism runs into some nasty divergences at large energy scales, so we need to consider a bigger symmetry group than that. This smallest such group gives electroweak theory. This answers your question about whether you can remove the electromagnetic interaction. The answer is "no" because that would severely mess up the weak interaction, so you'd have to remove them together!

Once you have this gauge symmetry, some quantum processes can violate it. Such processes are called quantum anomalies and they need to cancel out. The standard model has this anomaly cancellation feature, but part of the cancellation involves quarks and involves the fact that they have 3 color charges. This means that we need to have the strong nuclear interaction in the mix as well! I'm not sure if it's the only way to achieve anomaly cancellation, but if there are other ways they're definitely not obtained by slight deformations of the standard model. If there are no other ways to cancel the anomalies, then the standard model is actually the smallest model with interactions, whose particles transform properly under Lorentz transformations, that make sense at high energies and doesn't collapse into a negative energy abyss...

You can in principle have larger gauge groups without any immediately obvious problems, but the examples so far are a good reason to be cautious about just slapping new interactions on top of everything. You definitely have to check for renormalizability and anomaly cancellation every time you throw in a new ingredient.
Each new gauge group comes with its own coupling constant, which is independent of the rest, so that's the part that's not constrained (however their dependence on energy scale definitely depends on the other interactions).

So the bottom line is that the types of particles we can have are constrained, the form of the interactions is somewhat constrained but not entirely, and the relative strengths of the interactions are not constrained at all... I don't know if these match your definition of "meaningful constraints".


So whats the relationship between energy levels and the number of virtual particles generated at a certain energy level. How can an interaction in any type of field theory produce infinite energy? Do you have an example? Even if it does produce infinite energy why not just use renormalization to fix the problem. So basically from what I understand from reading that is the reason the universe exists is to get rid of infinities.

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Re: Are physics in the particles, or reality itself?

Postby elasto » Thu Apr 03, 2014 11:02 pm UTC

quarkcosh1 wrote:What exactly do they mean by too simple? Also do those unpredictable universes have no laws of physics? How unpredictable would they be?

They talk about it briefly in the text:

By 'too simple' they mean the universe is probably too simple for intelligent life to form - eg. complex brains are not possible (neurons cannot cross in 2D). And also gravity is problematic so no stars and planets and presumably no elements beyond helium.

And 'unpredictable' loosely means no well-defined 'cause and effect', which, again, means intelligence is unlikely to evolve, so such a universe will likely not contain any self-aware observers.

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Re: Are physics in the particles, or reality itself?

Postby eSOANEM » Thu Apr 03, 2014 11:15 pm UTC

Actually, I believe doogly said that unpredictable in this case means that the differential equations you need to solve in order to do physics no longer guarantee the existence of solutions. Solutions must exist for the universe to behave as it does (because stuff happens) and therefore the universe does not have that many dimensions.

Edit: I think you also run into problems with trying to define causality in those universes, but existence of the universe is a more fundamental problem than whether it is causal or not :p
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