I wonder if it's possible to ever find out what our reality is even if we will eventually reach the intellectual and technology necessary because we are part of it and it's probably impossible to have an objective view of the matter.
"There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable." – from The Restaurant at the end of the Universe.
I often think about that quote when I'm thinking about the universe as being a simulation in someone's computer somewhere. So imagine us clever little monkeys on the inside, have been probing the behaviour of the simulator by conducting science experiments. We're basically conducting targeting fuzzing of the simulator, which probably results in quite a few bugs going off. At which the compsci student running the simulation sighs, corrects the bug, and launches the simulation again.
"Any effectively generated theory capable of expressing elementary arithmetic cannot be both consistent and complete. In particular, for any consistent, effectively generated formal theory that proves certain basic arithmetic truths, there is an arithmetical statement that is true, but not provable in the theory" - Gödel (Kleene)
The thing is, the universe and mathematics are totally separate entities. The universe did not start off "as math", nor is it defined by it.
We, as clever little beings found similarities and analogies between the universe and mathematics and leverage those to make conjecture regarding the form and nature of the universe. However, having a "complete" knowledge of either mathematics or the physical universe does not confer complete knowledge of the other.
Physics (and science in general) isn't about searching for the Truth. Instead it's about reducing the amount of error in the mental models we use to approximate reality. Like, when a scientist says "the Law of Gravity", they actually mean "our best current guess as to how gravity works, which seems to make accurate predictions in what we consider a statistically significant number of different scenarios, but which is incomplete and perhaps even completely wrong in several other interesting scenarios or edge cases". Only _everything_ in science has a confidence interval, and prefacing every description of some phenomena with the phrase "we're pretty sure this is how this works, but to be perfectly honest, it's only an approximation to some X degrees of accuracy" gets really exhausting, so for stuff we're really, really sure of, like 99.9999% sure, we call it a "Law" (even though it isn't) and move on with our lives.
There is this belief propagated among physicists that smaller scales somehow have more to do with reality. I have never been presented with logic or evidence that convinced me that an electron is somehow more "real" than a molecule or a person or the solar system or the observable universe.
I wish the word "reality" would stop being thrown around without justification. "Fundamental" might be a more appropriate term.
>There is this belief propagated among physicists that smaller scales somehow have more to do with reality
Only among high-energy physicists. Perhaps not coincidentally there's also a belief among high-energy physicists that only they count as physicists.
In reality, they're a small minority of physicists. The largest specialty in physics, accounting for about half of all research, is condensed matter physics. Then in no particular order you've got AMO (atomic/molecular/optical), astrophysics, geophysics, biophysics, and a bunch of other stuff sitting between or outside those categories. With the exception of just a few corners of astrophysics, none of these fields needs, or can make sure of, the stuff being done on fundamental interactions; regular old quantum mechanics plus relativity is good enough for describing everything we can actually measure.
It easier to get a detailed understanding of the universe, by observing what happens in extreme cases. The very small. The very big. The very heavy. The very energetic. The very quick.
I guess you mean "elements." We used to apply the word to earth, air, fire and water. Now it is all about tachions and whatnot. But elements is the word.
For the moment it seems to me that there is no chance to ever know what something REALLY is. There is obviously stuff out there that behaves exactly like mathematical models we made up - there are things called electrons behaving like our model of electrons interacting with things called photons behaving like our models of photons. But what does this tell you about the nature of electrons and photons? Is a electron just a handful of numbers like charge -1 and spin 1/2 behaving according to the laws of physics or is there more to an electron? I can't even imagine how one could bridge the gap between our models of reality and reality but then there is probably so much more to learn about our universe, maybe some day...
Maybe asking what things REALLY are has no meaning. Do objects have characteristics apart from what we can (physically) interact with and measure ? If thoses characteristics exist but aren't measurable can we say they are real ? Does it make any sense ?
I often use this line of thought to talk about God with open-minded believers. If there is a God that created our reality and acts on it, then the effects of these actions are real in our sense and thus measurable. It then follows that God isn't separate from the natural world and can be observed like many other natural phenomena we don't look at directly. Without a chain of interactions this wouldn't be possible.
What I mean is our reality is one of interactions. What is real to us, and what can be called "existing" is what interacts directly or indirectly with our senses and our minds. What we mean by "nature" on a large scale is ultimately internal structure. Once we hit a level where internal structure doesn't make sense anymore, I'm not sure what we are looking at and what the word "nature" can be made to encompass.
Why are all electrons the same? It's because they are all manifestations of the same electric field. But then what is the electric field? Yep, it's a rabbit hole.
Any physical system that can be described by a set of mathematical laws is bound to have some axioms that simply cannot be proven within its context. Godel's incompleteness theorems prove that.
Hence, we will never get to the bottom of the reality of our universe.
Your statement that we will never get to the bottom may be true, but the reasoning is flawed.
Gödel's incompleteness theorems are about mathematical theories, not about physical theories. It may well be that for physical understanding a very limited arithmetic is sufficient. Also, there may be statements that are unprovable, but these might turn out to be irrelevant to sufficiently understanding the universe.
Also, an axiom, by definition, can not be proven. The things that are proven are theorems, statements, etc. An axiom is an assumption.
Eventually, it all depends on what level of understanding you want. But Gödel's theorems have little to do with that.
From the mathematical point of view, physics is about finding smallest set of axioms from which you can mathematically derive complete theory of universe's behavior. Validity of such axioms is in turn validated by experiments (by testing whether results match theory derived from given axioms)
It is true that they will never be "proven", but that doesn't mean we can't build a tremendous confidence in them through experimentation. (Which is to say "I agree", but I wanted to put a slightly different spin on it.)
The incompleteness theorem describes a tradeoff: A system of axioms cannot be both consistent and complete. But that seems irrelevant, since you could make a system that describes all of physics while not being either consistent or complete. https://en.wikipedia.org/wiki/G%C3%B6del%27s_incompleteness_...
Scientific reasoning is inductive, not deductive. When doing inductive reasoning you are allowed to update your belief in your axioms based on the empirical evidence you see.
In fact, the theorem showing how to do so (Bayes' Theorem) is so utterly elementary we teach it in the first probability course everyone takes.
If reality is just math, then it boils down to everything being generated from axioms. Gödel does not tell us that we cannot discover those axioms (and that they are axioms).
Where Gödel comes into the picture is that he gives us no right to believe that only those axioms are all there is.
If the reality is mathematics, Gödel justifies the Multiverse hypothesis: just because we are objects within some theory doesn't mean there don't exist other theories (perhaps superset of this one).
"Unable to prove" in the Gödel sense can be then equated with "unable to peer into another universe".
Gödel's sentence becomes analogous to some phenomenon or artifact of another universe which cannot exist in ours because it cannot be derived from its axioms.
I agree with this but for a different reason. No matter how much we discover, everything we find is still something in existence. No matter what force or object you are observing, you can't doubt that it exists at some level, in some way (whichever multiverse or reality it is).
This means that at some point, existence must have been started by something non-existent. Because we only comprehend cause-and-effect, we can't possibly find the origin in a provable way while researching from within existence.
Godel's incompleteness theorems only place restrictions on deductive systems. In mathematics, you can't perform "experiments" and measure what happens. As long as we can observe and measure physical quantities, even if those quantities are only indirect effects of what physicists are actually trying to measure, incompleteness is not a strong limitation of physics.
This argument is always used to try to reduce the power of mathematics, but the whole fact that mathematics was used to prove this tells me otherwise. There is a huge amount of properties of the universe that can be understood with mathematics despite Goedel's result.
Not axioms, tautologies (true statements). Godel's incompleteness theorem assumes you know the axioms. Godel doesn't tell us whether we can discover the axioms, although perhaps it implies that as a corollary.
I didn't downvote, but if you ask me I'd say others did it mainly because grandparent brought philosophy into scientific discussion. (And with reasoning or phrasing issues at that: “we can't do something even if we can”, for example, contradicts itself.)
That's precisely why, IMHO, if you aren't prepared to make a complete well-thought-through argument, then you should think twice before venturing into a philosophical discussion.
On the other hand, due to the nature of HN, one has to choose between either spending a few days researching the comment and posting it with a very slim chance of being read or answered, or blurting out something not very polished.
In this case it's the latter. (How you define “objective”? “reality”? A rough example of how could the answer to the question “what reality is” roughly look like? Any links to existing research—people certainly attempted to ask a question of this nature before?) The resulting discussion may be worth it, though.
There's a very subtle undertone of negativity in this article about physics. Before I get into, William Bardeen is not in the same league as 'Surfer Dude and his E8 Theory of Everything' which throws basic facts about representation theory out the window, coming up with 'todalay boogus' arguments which amazes auntie, mommie and magazine editors but a real physicist would instantly dismiss.
Bardeen is the real deal. His papers are very interesting and feel a bit like reading Sidney Coleman's papers. If you're interested...
Is nature scale invariant? So far the answer is absolutely NO but I strongly advise to wait and see. There are many topics that point to some breakdown in scale or reorganizing what we think of space and distance (dualities in string theory, conformal field theory).
OK, now the important thing I want everyone here to realize. You are living through a GOLDEN AGE of physics. You wouldn't think that based on what all the popular magazines tell you. Here's why...
1. Higgs particle - discovered!
2. Inflation - discovered! Denying this one is like denying the Big Bang itself. The evidence is overwhelming and in fact I would list this as the single greatest scientific discovery of all time. The concurrent discovery of gravity waves, quantum gravity and a real life example of a Hawking process only sweetens the deal.
3. Supersymmetry has basically already been discovered IMHO. They aren't announcing anything at CERN and won't until they have so many sigmas under their belt but trust me, it's coming and truth be told, it isn't really so surprising. SUSY physics has always been rock solid from the beginning. The situation is very similar to that before offical Higgs announcement and before someone went knocking on Andre Linde's front door. Many were extremely confident in the Higgs particle a least a year before the official announcement. The BICEP 2 results were even more glaringly apparent than the Higgs results. Many people were walking around the Earth with 'secret knowledge' that inflation theory was correct even 2 to 3 years before the official announcement.
So you are living through EXTREMELY interesting times but you wouldn't know it with all the big science bashing being thrown around.
I study astrophysics, so I won't be able to say much about SUSY or string theories or conformal field theories. I do agree that we're living in a golden age of physics! But your second and third points, inflation and SUSY-- those are definitely not confirmed. In fact, the primordial gravitational waves from BICEP2 are almost certainly dust contamination signal (e.g., http://arxiv.org/abs/1405.5857). The discovery of supersymmetric particles would also be extremely shocking to me, since my institution is heavily involved in CERN LHC experiments, and I haven't heard any hints of a discovery yet. Perhaps you know something that I don't!
> The discovery of supersymmetric particles would also be extremely shocking to me, since my institution is heavily involved in CERN LHC experiments, and I haven't heard any hints of a discovery yet.
Why does an absence of evidence imply that the arrival of evidence would be shocking? They're doing the experiment because they already believe things are this way and they're trying to get evidence to confirm it. If they disconfirmed it, that'd be surprising.
> They're doing the experiment because they already believe things are this way and they're trying to get evidence to confirm it.
That's not science, that's confirmation bias. In science, one would want to look for evidence that one's theory is false with as much vigor as a search for evidence that it's true. Science isn't law, and it's not religion.
> If they disconfirmed it, that'd be surprising.
If they falsified their theory while only seeking confirming evidence, yes, that would be surprising. This is why open-minded scientists try to avoid assuming what they should be proving (the real meaning of the expression "beg the question").
I'm not trying to start an argument here, but wouldn't "assuming what they should be proving" be the same as "hypothesizing?" That's a critical point of the scientific method. You don't really design experiments that can both confirm and refute a theory. When an "open-minded" scientist attempts to perform an experiment to test theory, they aren't personally responsible for subsequent theories and experiments that could disprove their results.
> wouldn't "assuming what they should be proving" be the same as "hypothesizing?"
No, the expression "assuming what you should be proving" has a special semantic meaning -- it refers to a thought process that uses its conclusion to support its investigation, or takes the preferred outcome as a given from the start, without seriously considering alternative explanations.
Hypothesizing means taking existing theory and extrapolating new untested properties, then presumably investigating whether there is any evidence for the hypothesis.
> You don't really design experiments that can both confirm and refute a theory.
On the contrary, the best experiments have the chance to either confirm or refute a hypothesis. The Michelson & Morley ether experiment is a classic of its kind -- its outcome would either confirm or refute the ether as it was imagined to be.
> When an "open-minded" scientist attempts to perform an experiment to test theory, they aren't personally responsible for subsequent theories and experiments that could disprove their results.
Not so. An open-minded scientist wouldn't pass up the chance to uncover any positive or negative evidence for or against his theory -- both kinds of evidence contribute to our understanding of nature. Remember the story about Bell Labs engineers Penzias and Wilson cleaning bird droppings from their microwave dish? They did that so someone else wouldn't scoop them by discovering that they had been fooling themselves about the source of the noise in their antenna (which ultimately was identified as the cosmic background radiation, now standing as evidence for the Big Bang).
The bottom line? Science isn't law, it's not adversarial, there aren't two competing sides, and a responsible scientist maintains an open mind with respect to evidence both for and against his theories.
No. One of the most commonly used definitions of faith is trust or confidence in a person or thing. Whether or not that trust or confidence is based on evidence or not is a separate matter that is not conveyed by the word.
Even in the case under discussion, that someone might have faith that something is a particular way, and are doing an experiment to confirm it (more likely disprove an alternative), that doesn't mean it's 'blind' as in without reason. People can have a lot of good reasons for believing something is a particular way without having measured it directly yet.
Not confirmed in the sense that many in the community are denying the result, which is as it should be. Even considering many models including dust a robust result remains. I think PRL and others are being unreasonably pessimistic but the only way to settle this is for there to be more experiments at different frequencies. Then they can move from the shock and denial phase onto the grieving process. BICEP scooped Planck, big time. It doesn't matter to me but it matters a whole lot to some people and the degree of sour grapes and poor sportsmanship is really stunning. Yes, I am saying a good deal of this is motivated by the tiny team beating the much bigger team though I absolutely disagree with their hypercompetitive interpretation of the whole enterprise of experimental physics. History will tell us that BICEP got lucky, very lucky and they got there first. The dust up is happening on Earth not in space and the latter is certainly much easier to explain away and still have at least a six sigma result. I've read the dust papers with an open mind and none of them add up.
Regarding SUSY, strictly speaking no particles have been directly detected but anomalous currents abound and just about everything seen works perfectly with light SUSY and much better than with the standard model. The dilepton events alone are very compelling. http://www.science20.com/a_quantum_diaries_survivor/a_susy_e... SUSY is in plain view much the way the Higgs was in plain view for about a year before the official announcement. I have no special insider information, just a humble internet connection to download the important papers and a decent knowledge of particle physics. In hind sight, everyone will say 'of course' which always happens. From a theory point of view, SUSY is simply not an option unless there is some spectacularly new theory out there with novel concepts to replace QFT. The Coleman-Mandula theorem is extremely compelling. It basically tells us accept SUSY or find something to replace QFT. Since QFT works and there's no good reason to move on to something else (especially when something else doesn't exist presently and possibly never will), it's a safe bet SUSY must exist somewhere. It just so happens to be light SUSY and we're seeing it at the LHC right now. I think we're presently seeing the equivalent of a COBE picture of SUSY and next year it will sharpen up into a WMAP picture.
Are there any particular resources that you recommend for a high-level overview of this kind of stuff? I'm an engineer with a solid grasp of classical mechanics and strong math background, but very little exposure to modern physics (basically, anything discovered after 1905) and I would like to be able to read about and appreciate this type of work. Where to start?
Apologies for taking the conversation off on a tangent, but you seem passionate about this.
Do you have any rumors or specific knowledge (even if it's not something you'll share) regarding SUSY? They found missing energy? A new plethora of resonances? Higgsinos or sfermions? Something more exotic?
By the end of the last run, the people I talked to at CERN were fairly certain that there's no SUSY in the current dataset and that SUSY will likely not be found during the upcoming run. But perhaps the people I talked to are simply of a different persuasion.
Thanks for your post and link. I recently watched Particle Fever on Netflix and became extremely fascinated with the field. A lot of the information you posted is touched on in the documentary. It is mostly focused around CERN and the years leading up to the Higgs particle discovery. There are also great interviews with David Kaplan and Nima Arkani-Hamed.
You've likely seen it but if not you might enjoy it.
Surfer Dude and his E8 Theory of Everything ... 'todalay boogus' arguments which amazes auntie, mommie and magazine editors but a real physicist would instantly dismiss.
I suppose you're referring to Lisi? Neither he nor E8 were even mentioned in the article. You're both OT and unnecessarily unpleasant.
Well there is no way Lisi's E8 theory can fit gravity and the standard model at the same time. At first glance the group structure seems to allow it but the actual group representation (which are the actual particles allowed if one wishes to construct such a theory) don't allow it. I'm totally fine if someone wants to pursue this area of research the problem is the MAGAZINES have printed his theory as though it were a valid contender or alternative to string theory or some other theory. Lisi's theory isn't. If it were a plane, it never got off the ground, it blew up on the runway. A recent TIME magazine special issue features this broken 'theory'. It's deeply misleading and shows a lack of concern about misleading the public. Loop quantum gravity, simplicial quantum gravity, and causal sets etc. are all examples of broken theories that just don't work. Just so you know there ARE valid alternatives to superstring theory regarding unification or physics beyond the standard model. Alain Connes non-commutative gravity, superconformal field theories, Kac Moody algebras, twistor gravity, twistor string theory, plain old N=8 D=4 supergravity is a contender, SO(10), SU(5), MacDowell Mansouri gravity, matrix models,... I could list more. These theories aren't broken, they actually work. Those are the kinds of things the public deserves to hear and read in the magazines.
The road from theoretical physics to engineering is a very long one, so it's very hard to predict exactly what this would buy us. Relativity, for instance, spent a long time with no concrete engineering benefit, but now it allows GPS to be much more accurate by adjusting for the time dilation on GPS satellite clocks. As we get closer and closer to the mysteries at the heart of the universe, I think it's safe to say that the engineering benefit will be both more arcane and more powerful.
A lot of discoveries do not have immediate uses and some might indeed never have any applications. But discoveries can spurn others in unexpected ways. The most famous example of course if the WWW which came out of CERN, a pure physics research institution. Cryptography is another example that has had a profound impact on information security.
But the most compelling reason, at least to me, is we investigate because we can! That is just human nature.
Basic research is the foundation of all engineering. You can't design things without understanding how the universe works. If you need examples, look no further than to particle physics, which has had a huge influence on medical imagery since at least the fluoroscope.
All things hitherto designed have been designed without a complete and truthful understanding of the universe. If we go back in history, we find examples of useful inventions that were produced amid a rather poor understanding. Levers and inclined planes were produced without knowing anything about basic arithmetic, let alone physics.
of course. Natural thing when a field is dominated by orthodoxy that closes their eyes to everything that they don't want to see. Like yesterday "entangled photon imaging" where what really happens is that a beam modulated by an image heats/excites crystal (with that heating/excitement thus obviously modulated by the image) which generates another beam (thus that another beam is obviously also modulated by the image) which hits CCD - no miracle of entanglement here, yet Nature published it as such :
https://news.ycombinator.com/item?id=8234221
as "entanglement" and "mutiverse" are very much in fashion this season and get you published.
With Higgs as a "mass" boson it was also non-starter because the theory of it failed to address gravitational and inertial mass equivalence. I mean i don't doubt that CERN found new particle of course, yet nowhere it was shown that it is the boson "generating mass". The article seems to suggest that finally the mainstream physics starts to seriously ponder whether the mass is a result of dynamic interaction - that has been obvious for decades to the "fringe" physicists, who couldn't just dismiss the above mentioned gravitational and inertial mass connection, a pretty fundamental fact that has to be at the center of anything called physics :)
I wouldn't say that the "field is dominated by orthodoxy that closes their eyes to everything that they don't want to see".
I'll admit most physicists I've met are suspicious of wild-eyed theory. But I wouldn't say they're overly orthodox. I think it's more a healthy skepticism of anything which involves humans projecting science-ficiton wish-fulfilment into science.
I'd go further and say that "entanglement" and "multiverse" are not at all en vogue. I think most seasoned physicists realize that these were trendy fields some years ago (for solipsistic reasons - ie, make us feel special).
So I think the return to a fundamental assessment of phenomena is pretty natural thing. Calling out assumptions like scale. What's more, I think the more discerning will also be suspicious of the "post-multiverse" dialectic. It's just the process really.
>I'll admit most physicists I've met are suspicious of wild-eyed theory.
...
>So I think the return to a fundamental assessment of phenomena is pretty natural thing. Calling out assumptions like scale.
i see big difference between "Calling out assumptions like scale" as a "return to a fundamental assessment of phenomena" and "Calling out assumptions like scale" in order to fit it into a wild-eyed theory like superstrings (basically to salvage the theory).
I'm not sure why you're grouping entanglement in with the multiverse.
One of those is a theoretical idea for reducing the Solomonoff complexity of the universe with no clear experimental implications. The other is an integral component of how we predicted and explain experimentally confirmed phenomena like violations of Bell's inequalities, the Elitzur-Vaidman bomb tester, quantum cryptography, and quantum teleportation.
because both violate Occam's razor (and both stem from very specific treatment of superposition). Like in the above mentioned "imaging by entanglement", a closer look at the experiment always reveals explanations for the observed effect without necessity to involve the "magic" of entanglement.
Entanglement isn't magic: it's just correlation. Behind every pair of entangled particles you find a single original causal event that created them and entangled them. Entanglement just seems like magic because the actual reality is a joint distribution over particle states that already obeys the appropriate physics, but you're thinking of it as two separate distributions whose results are "forced" by "magic" to conform to the appropriate correlation after the "sampling".
There's no magic: you're just sampling a joint distribution in the first place.
>Behind every pair of entangled particles you find a single original causal event .... the actual reality is a joint distribution over particle states that already obeys the appropriate physics
that is exactly my views too. QM people call it "hidden variable" theory.
>two separate distributions whose results are "forced" by "magic" to conform to the appropriate correlation after the "sampling"
and that is Copenhagen interpretation superposition wave function collapse based theory of entanglement.
>you're just sampling a joint distribution in the first place.
if somebody shows that Bell violations can happen here too the Nobel prize will be his/her. I though think that Bell violations can't happen at all. That would be another Nobel prize i guess :)
>How do you explain Bell inequality violations without involving entanglement?
i still can't in details :) I so far have worked my way only until double-slit experiments - no superposition there :) For Bell violations i bet we have the same mis-interpretation of statistical aggregate description as individual realization (this "mis-interpreation" is the Copenghagen's superposition) as in double-slits. In case of Bell violations experiments it seems to be the same as "disjoint sampling loophole" http://en.wikipedia.org/wiki/Loopholes_in_Bell_test_experime...
>If we get quantum computers working at a non-trivial scale, would you consider that to be strong evidence for entanglement?
it would be strong evidence for superposition and thus for entanglement. Want these computers like anybody else, yet don't really see them happening :(
I don't see why this kills the multi verse theory.
Which is a basic conclusion of a 10 dimensional space-time environment that doesn't include mass anyway.
Well, it's just a hyperbolic headline that tries to call a speculation a theory (the latter meaning an idea with some supporting evidence). It certainly doesn't kill any other current speculation. It's journalism masquerading as science.
It "kills it" because it's only really appealing if the universe we're in appears extremely unlikely, like it's the "just right" goldilocks balance of cosmic variables that we can't explain, that happened to be the stable ones that resulted in life evolving eventually.
If the universe is actually very likely to occur in the state that it's in, then we don't need to use this "vast multiverse where our universe was the one that produced an observer" explanation. It could be a single universe in all of existence, where everything makes sense mathematically and no further posturing is required in that silly unscientific field of cosmic philosophy.
Or if it fails, and it remains that our universe is unexpectedly perfect, then we are forced to resort to statistical explanations within an impossible-to-observe external multiverse. Scientists don't very much like conclusions built on not being able to observe things.
Though to me, the multiverse theory has a sort of fractal appeal to it. It is surely applicable to our planet, after all. Why not our entire universe?
A cool thing about the multiverse is that it makes a team out of us and the rest of our universe. 'We' are the universe that became stable and self aware, in contrast to many other universes. 'We' are a self aware universe. You, me, and the rest of the universe together, so we should act like it.
If mathematical logic is a property of our universe, then aren't we again entering the realm of circular logic? i.e: "Given the logical frameworks that are correct in our universe, our universe is very likely."
Unless math is something that somehow exists independently of our physical universe... but then "where" does it come from?
My hunch is that mathematics is more than universal; truths hold regardless of which medium of calculation is used to conclude them.
In any case, our conclusions about our own universe at least hold within our own universe, and are therefore still very useful for our own understanding thereof.
But the whole point of the multi verse model is that universe also exists.
Multi verse theory afaik is just a mathematical construct of the various dimensions we can observe in a space time framework.
You're thinking of parallel or alternate universes, which is based on the "many worlds" interpretation of quantum mechanics, where the universe "forks" at every quantum possibility into an infinite number of universes. That's one type of multiverse.
A "Multiverse" is a superset of that idea—it simply means a condition of many universes existing. They could have arisen in the same way ours did through a "big bang" in some larger space alongside our universe, they could be the many iterations of our one universe expanding and contracting over an infinite time, or they could be overlapping in the "many worlds" sense; we don't know.
The point of a Multiverse set is to explain our universe's existence statistically rather than empirically (as in, with a satisfying observational explanation). It says "we know that the chance of our universe existing is extremely small, so we must be one in an infinite number that had the right combination to result in life."
This is sort of like a car crash, and saying: "whelp, it happens with a probability of 1 per 1000, so it was bound to happen to someone" after a car accident rather than finding out exactly why and what caused the event—"whelp, the brakes didn't work, we should probably look into that."
Just like that car crash, finding out exactly why our universe exists, and how likely it is to have the reality we enjoy, gives us far more information than a simple philosophical statistical conclusion. It doesn't mean that the statistical conclusion isn't correct—there still may be a Multiverse, we may never know—it just means we know more about it than just how often it happens.
But, knowing how likely our universe is to happen is a big step. If it's very likely, then we know a lot more about universes. If it's unlikely, then we could just chalk up our existence to chance and it would be perfectly valid. In the latter case, however, it would be extremely unsatisfying scientifically. We'd love to know more.
For a heroic attempt to explain this article to laypeople, check out physicsmatt's comments over at Metafilter:
"First, for maximum sense-making, read my previous comments here, here, here, and here. I realize that's a lot, sorry. The Universe is complicated. Then, for what follows, recall that to a particle physicist such as myself, there is no difference between lengths and energies (or indeed, any other dimensional quantity). Length is inverse energy: very energetic phenomenon probe very small lengths ...."
Or don't - it's incredibly badly written, in the sense that it often descends into grammatical gibberish, even without worrying about the physics the gibberish is trying to describe.
There's really not that much to understand, and the details aren't that important unless you're living them.
The question boils down to this: are we one of an infinite number of universes that popped into existence that just happened to have the right variables to be stable and result in life? (The anthropic principle, a statistical conclusion, and a philosophical mind-bender...)
Or are we in a single universe whose properties are mathematically aligned in such a way as to be very unlikely to result from chance, even if repeated an infinite number of times? The details of this are interesting, but extremely numerous and complex: basically, Physicists are trying everything.
The latter does not require the hand-wavey wishy-washy existence of an infinite number of non-observable extremely large things, and therefore garners more enthusiasm.
However, if observations conclude that the parameters of our universe are in fact paradoxically perfect, then the idea that we're an evolved observer of one chance universe out of many holds water.
Hence the intense research on how this whole universe thing works. Fun.
When I became interested in modern physics theories of both quantum and universe level, I found the following book [0] by Max Tegmark to have very good explanations regarding origin and nature of the universe, quantum mechanics, and just interesting stories / facts from the life of physicists.
> "Multiverse ennui cannot last forever" says Graham Ross?
That is naive. There is no way to prove or disprove it; it can be safely regarded as true without ever contradicting any possible observation we can ever make.
I do not think physics will ever settle the questions in such a way that the "multiverse ennui" is not invoked to cover the loose ends; in fact, it will become more and more obvious as the inescapable conclusion.
The deeper we dig into nature, either we keep finding more mathematics, or we encounter some absolute that can no longer be analyzed.
Once we know every physical law, and are certain nothing more is to be discovered, how do we distinguish our universe from a set of mathematical axioms? We have two choices then: to suspect there is some outer universe which implements the rules and axioms of this one. Or else admit that axioms do not require an implementation: they just are, and that's what makes their system exist (which means that any other axioms and rules we can imagine also exist just as much).
Either hypothesis is an unprovable "cop out"; but the latter of the two is more plausible. The first hypothesis still leads to an infinity of universes, and they have to be nested in each other in an infinitely regressing sequence. The second one has no such silly requirement; and it has the anthropic principle which plausibly explains everything that seems arbitrary or special.
To be fair, this only kills one of the multiverse hypotheses. I'm reading Brian Greene's "The Hidden Reality" right now, and he describes about 8 independent (or semi-independent) multiverse hypotheses. From what I understand (and I'm no physicist), this just provides evidence against the anthropic principle, and the multiverse associated with that line of thinking...
Things like this keep me wondering if eventually we will reach a point where we are unable to distinguish theories about our own past due to lacking the energy necessary to experiment with those conditions thanks to entropy.
Entropy = the inverse of available energy to do anything at all.
EDIT: Look -- if you don't understand physics, don't compound your ignorance by downvoting the posts of people who do. Instead, post a written objection, and I will explain why you're wrong.
I like to consider ∆S the result of a smoothing operation over energy differentials.
You can put work into a system to reestablish an energy differential. It just necessitates obtaining that other energy differential with which to do the work.
I feel like you're being that guy. Forgive me if I come across the same way.
Why link me to the Wikipedia article or insinuate I'm pulling this out of--to put it more politely--ex culo? Given my use of notation, one might assume I am at least a little familiar with how the thermodynamic entropy functions are mathematically derived.
To be pedantic for a bit, Entropy is an abstract mathematical state function useful for the prediction of thermodynamic systems. Much like the Gibbs and Helmholtz terms, entropy has no direct qualitative basis; there are many open-ended interpretations seeking to justify what it means, which is not unlike looking for God or faeries or what have you.
Mathematically speaking, I think you got your equality / definition wrong. Which energy function do you refer to? If you are still convinced about an error on my part, you can demonstrate in classical thermodynamics that,
S = "the inverse of available energy to do anything"
Or stats thermo, if that's how you roll. (Mine isn't that great anymore, sadly.)
What's my incentive to continue a discussion with someone who has abandoned the topic? In a closed system, the amount of exploitable energy, and the quantity called entropy, move in opposite directions.
> ... or insinuate I'm pulling this out of--to put it more politely--ex culo?
Point to where I said this. If you can't, then you have abandoned the topic.
> Much like the Gibbs and Helmholtz terms, entropy has no direct qualitative basis; there are many open-ended interpretations seeking to justify what it means, which is not unlike looking for God or faeries or what have you.
Nonsense. Entropy is clearly understood, it's not a philosophical puzzle as you suggest. It's easily quantifiable. It's science, not philosophy.
> Given my use of notation, one might assume I am at least a little familiar with how the thermodynamic entropy functions are mathematically derived.
Anyone can adopt the notations used in science. This doesn't tell me anything about their knowledge of the topics under discussion. You simultaneously apply standard terminology, but you go on to say that explaining entropy is "not unlike looking for God or faeries or what have you", which means you don't understand the significance of the symbols you used.
Entropy = k log(n)
k = Boltzmann's constant.
n = number of states the system can be in.
Quote: "Temperature is expressed as the inverse of the rate of change of entropy with internal energy, with volume V and number of particles N held constant. This is certainly not as intuitive as molecular kinetic energy, but in thermodynamic applications it is more reliable and more general."
Well, I don't think I understand entropy - even after Wikipedia. So is there somewhere in universe some energy that is not available to do anything at all? How does that work? Is it too diffuse such that the energy needed to pull it together to perform a unit of work is greater than the energy available ? If so how did it get to that state?
> Well, I don't think I understand entropy - even after Wikipedia.
Okay, here's a commonly used explanation. Entropy and time are bound together -- as time passes, overall entropy increases (with local violations like us). This is one idea about why time "moves" in the direction it does -- if time were to reverse, we could tell because some classic entropy results would run in reverse, violating common sense.
Imagine that there's a room, and in one corner of the room there's a perfume bottle. At time zero, the cork is removed from the perfume bottle. Because of entropy, the tendency of isolated systems to move from order to disorder, the perfume disperses through the room.
Ask yourself what the probability is for the perfume to spontaneously recombine in the bottle, versus the probability that it will disperse through the room. That probability differential is a measure of entropy.
> So is there somewhere in universe some energy that is not available to do anything at all?
Sure -- any isolated system can eventually get to a point where no useful work can be performed. Imagine an engine without any temperature differentials anywhere, or any way to acquire a temperature differential from an external source. Such an engine cannot do useful work.
A steam engine requires a heat source and a heat sink. Without a temperature differential, the engine cannot function. Same with a gas engine.
> Is it too diffuse such that the energy needed to pull it together to perform a unit of work is greater than the energy available ?
But without tapping an external energy source, the energy in an isolated system won't concentrate itself or spontaneously create a temperature differential suitable for exploitation. In an isolated system, the level of disorder always increases over time.
> If so how did it get to that state?
Simple physics. For two masses having a temperature difference, one with temperature "a", the other "b", and a temperature conductivity of "k", they will eventually reach the same temperature this way:
Δ = (b-a) e^(-t k)
Δ (delta) = temperature difference at time t
a = temperature a
b = temperature b
t = time
k = energy transfer coefficient
The above refers to an isolated system with an initial temperature difference. As time passes, that difference declines.
> Entropy and time are bound together -- as time passes, overall entropy increases (with local violations like us). This is one idea about why time "moves" in the direction it does -- if time were to reverse, we could tell because some classic entropy results would run in reverse, violating common sense.
As an aside, this is my own pet theory as to why some actions of living beings seem to resist scientific prediction. Observed within its own boundaries, a living being appears to be a system that locally decreases entropy; therefore within those boundaries it does not appear to operate causally.
So for example we can predict a human being who is deprived of food will die (basic energy balance), but we can't use science to predict what color shirt they will choose to wear next Tuesday.
If the available energy is dispersed and chaotic, we won't be able to concentrate enough to perform the experiments? Though I doubt that'll be the case at any time while the human race is in existence...
If humanity lives to a point where entropy becomes a problem, I'm pretty sure our lives would be the first to go, not our "ability to perform experiments".
that entirely depends on the magnitude of the experiment.
If we were approaching any "universal energy" limitations, it'd stand to reason that our technology would be very much different than our technology now -- perhaps universe sized experiments would be feasible by that point, at which time we may hit a limit imposed on us not by anything other than the length of time since the last universe formation event, and our poor luck in meeting that point in technology at a time where the energy no longer exists to fuel it.
Unlikely, and I think your idea of life being threatened before science is probably much more rational, but it's fun to think about. Plus, if we were using that much energy for a single experiment, one would wonder about that experiments' safety.
You should first worry about how we get out of this planet before the Sun turns into a red giant and swallows the Earth after 5–6 billion years from now.
Please have some perspective. Human beings have existed in roughly our present form for 200,000 years. In another 200,000 years, chances are we won't recognize ourselves. And in 5 billion years, which is 25,000 times farther into the future, there will be nothing remotely resembling human beings. We won't be a distant memory, we won't be a memory at all.
I had a scheme, once, for everyone to be remembered. It started with one nearly impossible scheme, producing a biography for every person ever (starting with the living, with some effort made to recover as many of the deceased as are still remembered today). The problem with that is that being recorded is not the same as being remembered. Being remembered means that someone living knows about you and thinks about you. They occasionally ask themselves what you would think or do.
So you would need a system for everyone's life to be read from the recordings periodically, by at least one person. For the near future -- say a few thousand years -- this could work. For the first few generations, each living person could remember a small handful of the deceased, and all of the deceased would be held in living memory. Once the number of people to be remembered grew too great for that, you could still cycle them in from time to time. Being remembered by one person every thousand years could still be pretty nice.
But five billion years, that dog don't hunt. At current generation lengths, there'd be 200 million generations to be remembered. Unless you are willing to postulate either constant, exponential population growth, dramatic lengthening of generations, or superhuman capacity to remember, you couldn't remember any one person more than once every several million years. It still beats being forgotten, if that's your fear, but not by much.
That was my point. Natsu was worrying about the ability of a technological civilization to function near the heat death of the universe. Which is much further than 5-6 billion years away. A more "immediate" problem is the death of our own Sun.
> Natsu was worrying about the ability of a technological civilization to function near the heat death of the universe.
Unless by "heat death" he meant a cold death, current thinking has it that the universe will gradually cool off, and ultimately freeze, because of the endless expansion provided by Dark Energy.
The fact that the universe is expanding exponentially, i.e. with a positive second derivative, was the first shock. The second came when the implications of this observation began to sink in.
"Heat death does not imply any particular absolute temperature; it only requires that temperature differences or other processes may no longer be exploited to perform work."
I once read that "black holes orbiting each other follow the exact same mathematics as electrons orbiting protons", but I was unable to find the direct source. I did find another article comparing black holes to elementary particles:
They would naturally follow the same mathematics, since the formula for gravitational attraction and the formula for electrical attraction are both following the inverse square law.
> Perhaps the fundamental description of the universe does not include the concepts of “mass” and “length,” implying that at its core, nature lacks a sense of scale. This little-explored idea, known as scale symmetry, (...)
Ah, no, that's a completely different sense of scale invariance. In a fractal you still have to measure the sizes of different similar structures, and generally pay attention to length. It seems that this article is discussing a much deeper abandonment of length.
"That shit would be too much," Gupta said. "It'd be like that Dr. Seuss book Horton Hears A Who and shit. I read that when I was, like, six, and it totally weirded me out."
Actually it should feel more like a tall story from your uncle at a family dinner, that's not corroborated and doesn't even imply what he insists it implies.
That is, half of the article is trash and the other doesn't represent the science correctly.
So two things standing next to each other are the same size as one thing alone?
Damn hard to imagine. I would think "size" does not really "exist" but is a man made concept. And by its definition, two things next to each other form a "bigger" thing.
The article is badly written, but it doesn't really mean sizes are illusory (even if it says so at the beginning). It goes on to say that sizes and mass "spontaneously emerge" from lower interactions, which is to say, they become real for us.
But, to address your example: "So two things standing next to each other are the same size as one thing alone? Damn hard to imagine".
That might not hold for size, but a very similar thing does occur (and is proven) for speed.
If you are in a car that goes at 0.8 miles per minute, and you throw a dart that goes at 0.3 miles/minute, its speed is 1.1 miles/minute (the sum).
But if you travel at the 0.8x the speed of light and you throw something forward at 0.3x the speed of light, its speed is not 1.1x the speed of light, but c. That is, trying to add velocity doesn't get you faster than the speed of light.
> But if you travel at the 0.8x the speed of light and you throw something forward at 0.3x the speed of light, its speed is not 1.1x the speed of light, but c.
Not really. Velocities near c don't sum that way. And your reference doesn't support your claim.
If you add two velocities that are less than c, you can never get c, you always get something smaller.
0.8c + 0.3 c ~= 0.887 c (It's smaller than c)
At low speeds the effect still exists, but it's negligible. There is an important difference between "it doesn't exist" and "it's so small that if we forget it we will be fine".
It's so small that you must use floating point numbers with too many digits to calculate it. It's more useful to calculate the difference between the "relativistic" sum and the "classical" sum. Another way is to aproximate the formula with a Taylor expansion
Indeed it is. The only place I can think where such a small correction matters is in the GPS system. The accuracy of the GPS system depends on tracking down and eliminating every possible source of error, and to maximize position accuracy, two relativistic effects are accounted for:
1. The time dilation caused by the satellites' velocity, from Special Relativity.
2. The rate of time passage at orbital altitude compared to that at the surface, which reflects the gravitational well effect of General Relativity.
The two effects move in opposite directions, but they don't cancel out. The applied correction (to the orbiting clocks) is very small indeed, but enough to avoid a gradual but serious decline in positional accuracy over time.
Does anyone know of a general & special relativity simulator? That is, a program where I can setup various "thought experiments", by placing clocks and masses at various point in space, where they can have various acceleration profiles, and can communicate with each other, and run the scenarios? I never really understood the twins "paradox" and the explanations for the source of the asymmetry seemed hand-wavy and "because".
