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Question: Why do some physicists believe it's a problem that physics isn't unified? It seems odd to assume that just because throughout history we've unified m

Question: Why do some physicists believe it's a problem that physics isn't unified? It seems odd to assume that just because throughout history we've unified more and more concepts that all of physics can be unified. What if there's a limit? It's interesting to think that 100,000 years from now, physicists will still be working on the problem since no one would know it's impossible.

stargazer-3 13y ago
It's not odd. To me it is only logical to assume that if we can explain most physical phenomena, the trend may very well be extended to the rest of them. Besides, one can find a surprising amount of symmetry, simplicity and beauty in the Universe. Note: I left the "some physicists" part of your question out of the answer because some physicists would believe in anything.
rosser 13y ago
Because physicists believe in parsimony? Less flippantly, simply that if the two (on their own, staggeringly accurate) main theories we have about how the universe works are as fundamentally incompatible as the ones we've got, then there's probably something we don't yet understand about the thing they're describing. The search for a ToE isn't so much about "unifying" QM and Relativity as it is about figuring out what it is that we don't yet understand about the universe that allows them both to be as true as they appear.
- laander 13y ago
  I am blasted away by your completely staggering domain-knowledge and my lack of the same. Probably should stop seeing universe docus and study more science
  - eru 13y ago
    Math is hard. And understanding real science often involves understanding math. (And docus almost never go into the math parts.)
richardjordan 13y ago
You either believe in natural or supernatural explanations for the universe. If you accept the latter then the discussion is moot. If you're a scientist your approach is the first. It is difficult, perhaps impossible, to come up with a philosophically sound logically consistant explanation for natural phenomenon which isn't unified and connected at a fundamental level. Two incompatible sets of natural explanations are vastly less likely than one unless we're falling back on superstition again. Hence on some level there will be a unified way of approaching and talking about physical phenomena. Now, is that underlying consistent theory achievable? Well that's a different question. If the unified explanation for all natural things, at its heart, relies on physics we just don't have access to - either it's too small scale for us to ever probe, or too large scale, or no longer manifested at this point in the universe's life (there are examples of this I could describe but that'd make this post too long) - then of course we would not ever get to a satisfactory scientific account which is unified. But efforts to get there tend to reveal other interesting things so are worthwhile even if we never achieve the final goal. Plus because it's so specialized and inaccessible to the layman, the degree to which there's already tremendous consistency and unification in our theories of the underlying nature of things is dramatically underappreciated by most people.
- sillysaurus2 13y ago
  It is difficult, perhaps impossible, to come up with a philosophically sound logically consistant explanation for natural phenomenon which isn't unified and connected at a fundamental level. Two incompatible sets of natural explanations are vastly less likely than one unless we're falling back on superstition again. Really? Ancient philosophers argued that it's vastly less likely for there to be such a huge distance separating celestial bodies than whatever their pet theory of the day was. Or that it's vastly less likely for planets to travel in ellipses, because circles were "so perfect." Throughout history, time and time again, humans seem to have a problem accepting that the imagination of nature is far greater than that of man. Plus because it's so specialized and inaccessible to the layman, the degree to which there's already tremendous consistency and unification in our theories of the underlying nature of things is dramatically underappreciated by most people. I'm trying, but unfortunately you've given no examples.
millstone 13y ago
Per my understanding, there's less concern over unifying, say, the strong and electroweak interactions. You have to posit some ridiculous coincidences to explain facts like why the charge on protons and electrons are exactly opposite, but nothing whatsoever prevents you from doing so. Then you get separate, compatible theories describing separate domains. That's basically what the Standard Model is: QCD + electroweak, agglomerated as separate interactions, not unified. However there's better reasons to be concerned with the relationship between general relativity and quantum mechanics. The problem is that while their domains are generally separate, we know they must intersect in cases like black holes or the early universe. And in these scenarios, the theories produce incompatible predictions, leading to issues like the black hole information paradox. Physicists are very interested in any theory of gravity that makes predictions compatible with quantum mechanics. Some of the contenders unify with the other forces (string theory) while some do not (loop quantum gravity). A unified theory would be huge, but a non-unified "agglomerated" theory that nevertheless makes a single, unified prediction would be almost as exciting. So the answer to your question is that popular physics writing often uses "unification" as a shorthand for "unified prediction" rather than "a single interaction." That's what this article is doing: the referenced Wheeler-DeWitt equation is NOT a unified theory because it does not explain QCD or electroweak.
- nasht 13y ago
  not sure if it is ok to ask this here, but does anyone know of a blog where physicists might be discussing this and other aspects of time?
has2k1 13y ago
Depending on what phenomena a set of equations describe, if the equations break down at some point it becomes of interest to figure out the reason. The situation cannot be ignored because it hints that the phenomena may not be properly understood. The equations of general relativity do not hold on the quantum scale, and those of quantum mechanics cannot be used when gravity is large. This is a break down. The bridge between the two could be unifying the two "worlds" or have a damn good reason why not. Nature has a good motivator for unifying called black-holes. Inside black-holes you have large gravity and also quantum scale stuff that has been eaten or squished together or just tiny space. It would be rather difficult to solve the black-hole problem starting from scratch, as black-holes arise out of general relativity equations. So you start from quantum scale and cross-check with the other end or vice versa. If you are weary of the word "unify" from a philosophical perspective, then it may help to realize that the word unify comes to apply because we (humanity) have discovered and built up more knowledge from imperfect bundles. Suppose in 1906 (before quantum mechanics or general relativity) Einstein had come up with some universal theory/model that inherently worked everywhere, it probably would never have been termed as a unification theory.
ssivark 13y ago
Simple answer -- There are situations (like black holes, or early universe physics) where gravity becomes very strong and important, and so do quantum effects. To understand physics in those regimes, we need a consistent way to put together gravity and quantum mechanics. The explanation that gravity corresponds to the physics of the large scales and quantum mechanics to the physics of small scales is not quite true -- this description applies in our daily experience, but is not always the case.
thibauts 13y ago
Because either a thing has no measurable effect on our reality and is thus both unknowable and irrelevant, or it has a measurable effect on our reality and then this effects exists in virtue of a kind of relation that can be described, maybe. What is one can be unified in theory as it is in practice. What is two doesn't have to, and we will never try to because we don't know it.
analog31 13y ago
Perhaps the most forthright answer is because it's interesting. In my view the inability to live with contradictory theories is one of the things that makes science what it is, and also that propels science forward. Gravity and quantum mechanics is a grand example, but we're trained on countless little contradictions, such as why channels A and B of my circuit seemed to behave differently yesterday, though they are nominally identical. Letting a contradiction stand without investigating it would have to be a conscious mutual decision, in and of itself. Making that decision arbitrarily would be akin to making the contradiction a matter of dogma. This is why some folks struggle with cognitive dissonances that they perceive in religions. Otherwise, if the contradiction is discovered to be irreconcilable for a good scientific reason, that discovery will be equivalent to a unification. So it's a game where there's nothing in between winning and giving up, and no time limit. What we never know about contradictions is how long it will take to reconcile them. When I discovered the problem with channels A and B, I had no idea at that moment how or when I would solve it. We have to live with the remote possibility that unifying gravity and quantum mechanics will take 100,000 years.
conformal 13y ago
the idea of unification you reference is more of a process of simplification, with an eye to creating additional explanatory value. one of the best examples is that of the ptolemaic system of astronomy: prior to galileo speculating that the earth moved around the sun, everyone thought the earth was the center of the universe and that objects in the sky just naturally moved in non-linear spirals (epicycles) that needed endless corrections to be "correct". once galileo's system was applied, the complexity of making tons of extra corrections to track the path of some star was drastically reduced: these changes were now attributable to the earth's motion around the sun, and further the sun's motion in the galaxy. you may be right that there is indeed an ultimate simplification, but nobody knows where the rabbit hole ends.
ddebernardy 13y ago
"It seems odd to assume that just because throughout history we've unified more and more concepts that all of physics can be unified. What if there's a limit?" Think of that question as akin to Hilbert second problem[1]: he wondered if the axioms of arithmetic were consistent -- back then, it seemed likely. Gödel came along and showed that no proof of it can be carried out within arithmetic itself. In a sense, the problem isn't entirely solved; but we now do know that we can't know. Perhaps someone will come along one day and give a similar answer in physics. [1]: http://en.wikipedia.org/wiki/Hilbert's_problems http://en.wikipedia.org/wiki/Hilbert's_problems
yetanotherphd 13y ago
Feynman's comments on this are related: "People say to me, “Are you looking for the ultimate laws of physics?” No I am not. I am just looking to find out more about the world. And if it turns out there is a simple ultimate law that explains everything so be it. That would be very nice discovery. If it turns out it’s like an onion with millions of layers and we just sick and tired of looking at the layers then that’s the way it is! But whatever way it comes out it’s nature, it’s there, and she’s going to come out the way she is. And therefore when we go to investigate we shouldn’t pre-decide what it is we are trying to do except to find out more about it." http://amiquote.tumblr.com/post/2744225669/richard-feynman-on-doubt-and-uncertainty-if-you http://amiquote.tumblr.com/post/2744225669/richard-feynman-o...

stargazer-3 13y ago

It's not odd. To me it is only logical to assume that if we can explain most physical phenomena, the trend may very well be extended to the rest of them. Besides, one can find a surprising amount of symmetry, simplicity and beauty in the Universe. Note: I left the "some physicists" part of your question out of the answer because some physicists would believe in anything.

rosser 13y ago

Because physicists believe in parsimony? Less flippantly, simply that if the two (on their own, staggeringly accurate) main theories we have about how the universe works are as fundamentally incompatible as the ones we've got, then there's probably something we don't yet understand about the thing they're describing. The search for a ToE isn't so much about "unifying" QM and Relativity as it is about figuring out what it is that we don't yet understand about the universe that allows them both to be as true as they appear.

laander 13y ago
I am blasted away by your completely staggering domain-knowledge and my lack of the same. Probably should stop seeing universe docus and study more science
- eru 13y ago
  Math is hard. And understanding real science often involves understanding math. (And docus almost never go into the math parts.)

richardjordan 13y ago

You either believe in natural or supernatural explanations for the universe. If you accept the latter then the discussion is moot. If you're a scientist your approach is the first. It is difficult, perhaps impossible, to come up with a philosophically sound logically consistant explanation for natural phenomenon which isn't unified and connected at a fundamental level. Two incompatible sets of natural explanations are vastly less likely than one unless we're falling back on superstition again. Hence on some level there will be a unified way of approaching and talking about physical phenomena. Now, is that underlying consistent theory achievable? Well that's a different question. If the unified explanation for all natural things, at its heart, relies on physics we just don't have access to - either it's too small scale for us to ever probe, or too large scale, or no longer manifested at this point in the universe's life (there are examples of this I could describe but that'd make this post too long) - then of course we would not ever get to a satisfactory scientific account which is unified. But efforts to get there tend to reveal other interesting things so are worthwhile even if we never achieve the final goal. Plus because it's so specialized and inaccessible to the layman, the degree to which there's already tremendous consistency and unification in our theories of the underlying nature of things is dramatically underappreciated by most people.

sillysaurus2 13y ago
It is difficult, perhaps impossible, to come up with a philosophically sound logically consistant explanation for natural phenomenon which isn't unified and connected at a fundamental level. Two incompatible sets of natural explanations are vastly less likely than one unless we're falling back on superstition again. Really? Ancient philosophers argued that it's vastly less likely for there to be such a huge distance separating celestial bodies than whatever their pet theory of the day was. Or that it's vastly less likely for planets to travel in ellipses, because circles were "so perfect." Throughout history, time and time again, humans seem to have a problem accepting that the imagination of nature is far greater than that of man. Plus because it's so specialized and inaccessible to the layman, the degree to which there's already tremendous consistency and unification in our theories of the underlying nature of things is dramatically underappreciated by most people. I'm trying, but unfortunately you've given no examples.

millstone 13y ago

Per my understanding, there's less concern over unifying, say, the strong and electroweak interactions. You have to posit some ridiculous coincidences to explain facts like why the charge on protons and electrons are exactly opposite, but nothing whatsoever prevents you from doing so. Then you get separate, compatible theories describing separate domains. That's basically what the Standard Model is: QCD + electroweak, agglomerated as separate interactions, not unified. However there's better reasons to be concerned with the relationship between general relativity and quantum mechanics. The problem is that while their domains are generally separate, we know they must intersect in cases like black holes or the early universe. And in these scenarios, the theories produce incompatible predictions, leading to issues like the black hole information paradox. Physicists are very interested in any theory of gravity that makes predictions compatible with quantum mechanics. Some of the contenders unify with the other forces (string theory) while some do not (loop quantum gravity). A unified theory would be huge, but a non-unified "agglomerated" theory that nevertheless makes a single, unified prediction would be almost as exciting. So the answer to your question is that popular physics writing often uses "unification" as a shorthand for "unified prediction" rather than "a single interaction." That's what this article is doing: the referenced Wheeler-DeWitt equation is NOT a unified theory because it does not explain QCD or electroweak.

nasht 13y ago
not sure if it is ok to ask this here, but does anyone know of a blog where physicists might be discussing this and other aspects of time?

has2k1 13y ago

Depending on what phenomena a set of equations describe, if the equations break down at some point it becomes of interest to figure out the reason. The situation cannot be ignored because it hints that the phenomena may not be properly understood. The equations of general relativity do not hold on the quantum scale, and those of quantum mechanics cannot be used when gravity is large. This is a break down. The bridge between the two could be unifying the two "worlds" or have a damn good reason why not. Nature has a good motivator for unifying called black-holes. Inside black-holes you have large gravity and also quantum scale stuff that has been eaten or squished together or just tiny space. It would be rather difficult to solve the black-hole problem starting from scratch, as black-holes arise out of general relativity equations. So you start from quantum scale and cross-check with the other end or vice versa. If you are weary of the word "unify" from a philosophical perspective, then it may help to realize that the word unify comes to apply because we (humanity) have discovered and built up more knowledge from imperfect bundles. Suppose in 1906 (before quantum mechanics or general relativity) Einstein had come up with some universal theory/model that inherently worked everywhere, it probably would never have been termed as a unification theory.

ssivark 13y ago

Simple answer -- There are situations (like black holes, or early universe physics) where gravity becomes very strong and important, and so do quantum effects. To understand physics in those regimes, we need a consistent way to put together gravity and quantum mechanics. The explanation that gravity corresponds to the physics of the large scales and quantum mechanics to the physics of small scales is not quite true -- this description applies in our daily experience, but is not always the case.

thibauts 13y ago

Because either a thing has no measurable effect on our reality and is thus both unknowable and irrelevant, or it has a measurable effect on our reality and then this effects exists in virtue of a kind of relation that can be described, maybe. What is one can be unified in theory as it is in practice. What is two doesn't have to, and we will never try to because we don't know it.

analog31 13y ago

Perhaps the most forthright answer is because it's interesting. In my view the inability to live with contradictory theories is one of the things that makes science what it is, and also that propels science forward. Gravity and quantum mechanics is a grand example, but we're trained on countless little contradictions, such as why channels A and B of my circuit seemed to behave differently yesterday, though they are nominally identical. Letting a contradiction stand without investigating it would have to be a conscious mutual decision, in and of itself. Making that decision arbitrarily would be akin to making the contradiction a matter of dogma. This is why some folks struggle with cognitive dissonances that they perceive in religions. Otherwise, if the contradiction is discovered to be irreconcilable for a good scientific reason, that discovery will be equivalent to a unification. So it's a game where there's nothing in between winning and giving up, and no time limit. What we never know about contradictions is how long it will take to reconcile them. When I discovered the problem with channels A and B, I had no idea at that moment how or when I would solve it. We have to live with the remote possibility that unifying gravity and quantum mechanics will take 100,000 years.

conformal 13y ago

the idea of unification you reference is more of a process of simplification, with an eye to creating additional explanatory value. one of the best examples is that of the ptolemaic system of astronomy: prior to galileo speculating that the earth moved around the sun, everyone thought the earth was the center of the universe and that objects in the sky just naturally moved in non-linear spirals (epicycles) that needed endless corrections to be "correct". once galileo's system was applied, the complexity of making tons of extra corrections to track the path of some star was drastically reduced: these changes were now attributable to the earth's motion around the sun, and further the sun's motion in the galaxy. you may be right that there is indeed an ultimate simplification, but nobody knows where the rabbit hole ends.

ddebernardy 13y ago

"It seems odd to assume that just because throughout history we've unified more and more concepts that all of physics can be unified. What if there's a limit?" Think of that question as akin to Hilbert second problem[1]: he wondered if the axioms of arithmetic were consistent -- back then, it seemed likely. Gödel came along and showed that no proof of it can be carried out within arithmetic itself. In a sense, the problem isn't entirely solved; but we now do know that we can't know. Perhaps someone will come along one day and give a similar answer in physics. [1]: http://en.wikipedia.org/wiki/Hilbert's_problems http://en.wikipedia.org/wiki/Hilbert's_problems

yetanotherphd 13y ago

Feynman's comments on this are related: "People say to me, “Are you looking for the ultimate laws of physics?” No I am not. I am just looking to find out more about the world. And if it turns out there is a simple ultimate law that explains everything so be it. That would be very nice discovery. If it turns out it’s like an onion with millions of layers and we just sick and tired of looking at the layers then that’s the way it is! But whatever way it comes out it’s nature, it’s there, and she’s going to come out the way she is. And therefore when we go to investigate we shouldn’t pre-decide what it is we are trying to do except to find out more about it." http://amiquote.tumblr.com/post/2744225669/richard-feynman-on-doubt-and-uncertainty-if-you http://amiquote.tumblr.com/post/2744225669/richard-feynman-o...