Time is weird stuff. When you can tell what altitude your atomic clock is by the offset in its notion of time with the clock at your side, you start to get an inkling about that.
The professor who taught quantum mechanics at USC when I was there used to joke that God told Adam and Eve that it took 7 days to create the universe, but we know from our observations that it was closer to 14 billion years. Given these two data points we can calculate how close to the speed of light God was travelling when he created the universe ...
Interesting to think of time as actually stopped though to an outside observer. Not sure what a photon is when it isn't moving at all, perhaps a point with an electric field and equal and perpendicular magnetic field.
Smolin's book on time is interesting. One of the points he makes is that we are limited in our thinking about the universe by using a language that does not model time - mathematics. Sometimes I wonder if we want things to be fundamentally pure and stateless because we find change so stressful.
Yes, but this is a physics professor making jokes to an audience of physics students. Why shouldn't he refer to special relativity? It's part of his training and the training of everyone who can hear him.
I'd be more surprised if the joke came from, say, the professor teaching egyptian hieroglyphics.
Apropos of nothing at the time I took it the title was 'Modern Physics' which basically was the senior physics class and covered a mix of things from some cosmology, relativity, quantum mechanics, and various papers that had come out the summer before.
>> Warning: The central idea in today's post is taken seriously by serious physicists; but it is not experimentally proven and is not taught as standard physics.
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.
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.
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
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.
> It is difficult, perhaps impossible, to come up with a philosophically sound logically consistent explanation for natural phenomenon which isn't unified and connected at a fundamental level
Well, one could come up with some kind of model of "infinite complexity", different models of different aspects of the universe can never be unified because of stretches of "infinite complexity" "between them", like imagine a model of particle physics with an infinite number of ever "smaller" particles and no fundamental particles/forces, things made of smaller/deeper things ad infinity. I guess our current mathematics is even capable of describing such a thing. But since "more knowledge" means "more advantages / chances of long term survival" for a species, it wouldn't matter if there is no finite upper bound of understanding, we will still pursue science. And such a point of view would only support theories that violate Occam's razor and the principle of parsimony, it wouldn't really help.
...but it would make for interesting philosophy, if the people smart enough to formulate such a theory mathematically would wast their time doing metaphysical philosophy :) And I don't even want to imagine how such a theory could be bent and twisted by popular interpretation and cult leaders looking for scientific support for whatever new "religions". But overall I think some paths of thought, like this one, are better let unexplored - too many dark and weird areas and too little of use for the advancement of science: we'd better keep our Occam's razors sharps and minds aimed at simple and consistent explanations ;)
The problem is consistency with your approach. I am referring to theories that are consistent enough with each other to have useful predictive power. As you get bigger disconnects between theories their predictive power falls away.
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.
> 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.
Is it me or is that a bit handwavy? The Greeks or whoever else got things awfully right and other things terribly wrong. We have the benefit of hindsight so we can point at the latter category. It doesn't negate the former.
Seems like you could take any statement and say "oh yeah? well the ancients got stuff wrong!"
You're not comparing apples to apples when you compare ancient "theories" and modern scientific theory. Predicting that the sun will come up tomorrow, and why the sun will come up tomorrow are two very different levels of detail and granularity. The latter will have far more predictive power than the former.
No ancient theories had anything like the predictive power of modern theories, so were far less powerful. So when we talk about how the ancients had theories for this - we're talking orders of magnitude less complexity.
An analogy: when we were kids my brother took part in a guess the weight of the cake. The answer was 1.010 kg. My brother had guessed 1.005 kg and another boy had guessed 1.04 kg. They tried give it to the other kid - well his difference was "3 different" whereas my brother's was "5 different". Obviously anyone with a brain could see there was an order of magnitude difference in the precision of the two predictions.
Ancient theories are like that. Orders of magnitude less precise and therefore less predictive than modern theories. The differences tend to lead to dramatic differences in outcome making them fail to interweave in ways that are useful for us in the modern world - this is why, after all, we moved to the modern theories and they led to everything we have today.
Ancient theories didn't tend to connect in philosophically logical ways as do modern theories - this is reflected in their lack of predictive power. So when I say that the problems with tying theories together that modern physicists have are vast in our minds, but really amount to splitting hairs when we compare them to the differences between theories that preceded them, this is why.
I think that's a bit of a strawman. The pattern described was that we are often wrong because there's some factor about which we do not yet have the slightest clue.
Given for how long we've thought that we knew everything, it should hardly be surprising to find out that there's more to things than we know.
The key difference is that we no longer posit that we know everything. We assumed we knew things we didn't, in ancient times, and in the process relied on hand-waves to keep moving, until some scientifically minded folks got too frustrated with the inconsistencies and started to accept that perhaps we didn't know it all. Now we know we don't know, and use the inconsistencies to tell how close we're getting to knowing enough to have consistent understanding.
The key is that we continue to improve our ability to gather evidence about what the universe looks like, and insist that our theories keep pace with the evidence we're gathering. So, the previous hand-waves occurred in large part due to insufficient data, and unwillingness to look for more. We've moved past that, to a large extent.
Those ancient theories are not philosophically and logically consistent. It's why we had the scientific revolution and the enlightenment in the first place. Because there were holes in those accounts. The degree to which Physicists are talking about inconsistencies are tiny compared to the huge holes in theories than the very primitive and simplistic ideas of the ancients.
As to your ending comment. That's the point. Without studying physics you're not going to understand the degree to which it already all plugs together very well. We would have no electronics nor satellites without an incredible level of agreement between theories and experiment supporting a tightly interconnected set of theories - they weren't going to happen with any pre-scientific revolution worldviews.
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.
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.
"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."
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.
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.
"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.
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.
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.
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.
As a layman I don't understand the 'problem' with time?
To me, time is relative to 'timers'. So how I perceive the world passing is a function of a electro/chemical activity in my head. I'd imagine if you could somehow 'double' this function I'd perceive time at half the speed. And I imagine if you were to turn off my 'timer' the world would pass by instantaneously.
I've heard that 'time' is the fourth dimension? But again, as a layman, I have to ask why isn't 'thought' the fourth dimension? Isn't it only by being conscious, by being a 'timer', that 'time' can even be perceived?
Because time has a direction (for some reason it doesn't seem possible to go backwards though), and a value. I can't think of similar analogies for 'thought' that makes it fit with the other 3 room dimensions.
Or this is just a researcher stating to a reporter that he does not have proof, to avoid false headlines. The underlying reason of course being that there is not such a thing as "proof" in physics.
No they have proof in math. He is clearly saying it's not a proof to explain to the layman interviewing him that he shouldn't go and write some stupid headline like "physicists prove that time is just an illusion".
Agreed. Taking "ancient wisdom" too seriously and seeing it through a modern scientific lens is pretty much always too big-a-stretch to make.
Plus there's a difference between talking about psychological perception of time, as most religious texts do, and time as a measure of the evolution of physical systems in the scientific sense. Not the same thing.
How a time, that could be measured as a property of one physical process, say, radioactive decay is related to the time of another independent physical process, such as growth/maturation of a biological "system" called child?) Or rotation of a Moon around the Earth? There is no relation, except those based on mental concepts. To say that all these times are one and the same universal time is to create yet another mental concept.
This is one of those cases where the poetic language used to try to explain complex phenomena to lay persons is unhelpful. It doesn't really mean illusion in any sense consistent with what people might imagine that to mean.
Indeed it's not really that revelatory. "Experiment agrees with what we already pretty much know" would have been less interesting.
The professor who taught quantum mechanics at USC when I was there used to joke that God told Adam and Eve that it took 7 days to create the universe, but we know from our observations that it was closer to 14 billion years. Given these two data points we can calculate how close to the speed of light God was travelling when he created the universe ...
Interesting to think of time as actually stopped though to an outside observer. Not sure what a photon is when it isn't moving at all, perhaps a point with an electric field and equal and perpendicular magnetic field.