I’m on record as predicting that we’ll understand what happened at the Big Bang within fifty years. Not just the “Big Bang model” — the paradigm of a nearly-homogeneous universe expanding from an early hot, dense, state, which has been established beyond reasonable doubt — but the Bang itself, that moment at the very beginning. So now is as good a time as any to contemplate what we already think we do and do not understand. (Also, I’ll be talking about it Saturday night on Coast to Coast AM, so it’s good practice.)
There is something of a paradox in the way that cosmologists traditionally talk about the Big Bang. They will go to great effort to explain how the Bang was the beginning of space and time, that there is no “before” or “outside,” and that the universe was (conceivably) infinitely big the very moment it came into existence, so that the pasts of distant points in our current universe are strictly non-overlapping. All of which, of course, is pure moonshine. When they choose to be more careful, these cosmologists might say “Of course we don’t know for sure, but…” Which is true, but it’s stronger than that: the truth is, we have no good reasons to believe that those statements are actually true, and some pretty good reasons to doubt them.
I’m not saying anything avant-garde here. Just pointing out that all of these traditional statements about the Big Bang are made within the framework of classical general relativity, and we know that this framework isn’t right. Classical GR convincingly predicts the existence of singularities, and our universe seems to satisfy the appropriate conditions to imply that there is a singularity in our past. But singularities are just signs that the theory is breaking down, and has to be replaced by something better. The obvious choice for “something better” is a sensible theory of quantum gravity; but even if novel classical effects kick in to get rid of the purported singularity, we know that something must be going on other than the straightforward GR story.
There are two tacks you can take here. You can be specific, by offering a particular model of what might replace the purported singularity. Or you can be general, trying to reason via broad principles to argue about what kinds of scenarios might ultimately make sense.
Many scenarios have been put forward among the “specific” category. We have of course the “quantum cosmology” program, that tries to write down a wavefunction of the universe; the classic example is the paper by Hartle and Hawking. There have been many others, including recent investigations within loop quantum gravity. Although this program has led to some intriguing results, the silent majority or physicists seems to believe that there are too many unanswered questions about quantum gravity to take seriously any sort of head-on assault on this problem. There are conceptual puzzles: at what point does spacetime make the transition from quantum to classical? And there are technical issues: do we really think we can accurately model the universe with only a handful of degrees of freedom, crossing our fingers and hoping that unknown ultraviolet effects don’t completely change the picture? It’s certainly worth pursuing, but very few people (who are not zero-gravity tourists) think that we already understand the basic features of the wavefunction of the universe.
At a slightly less ambitious level (although still pretty darn ambitious, as things go), we have attempts to “smooth out” the singularity in some semi-classical way. Aguirre and Gratton have presented a proof by construction that such a universe is conceivable; essentially, they demonstrate how to take an inflating spacetime, cut it near the beginning, and glue it to an identical spacetime that is expanding the opposite direction of time. This can either be thought of as a universe in which the arrow of time reverses at some special midpoint, or (by identifying events on opposite sides of the cut) as a one-way spacetime with no beginning boundary. In a similar spirit, Gott and Li suggest that the universe could “create itself,” springing to life out of an endless loop of closed timelike curves. More colorfully, “an inflationary universe gives rise to baby universes, one of which turns out to be itself.”
And of course, you know that there are going to be ideas based on string theory. For a long time Veneziano and collaborators have been studying what they dub the pre-Big-Bang scenario. This takes advantage of the scale-factor duality of the stringy cosmological field equations: for every cosmological solution with a certain scale factor, there is another one with the inverse scale factor, where certain fields are evolving in the opposite direction. Taken literally, this means that very early times, when the scale factor is nominally small, are equivalent to very late times, when the scale factor is large! I’m skeptical that this duality survives to low-energy physics, but the early universe is at high energy, so maybe that’s irrelevant. A related set of ideas have been advanced by Steinhardt, Turok, and collaborators, first as the ekpyrotic scenario and later as the cyclic universe scenario. Both take advantage of branes and extra dimensions to try to follow cosmological evolution right through the purported Big Bang singularity; in the ekpyrotic case, there is a unique turnaround point, whereas in the cyclic case there are an infinite number of bounces stretching endlessly into the past and the future.
Personally, I think that the looming flaw in all of these ideas is that they take the homogeneity and isotropy of our universe too seriously. Our observable patch of space is pretty uniform on large scales, it’s true. But to simply extrapolate that smoothness infinitely far beyond what we can observe is completely unwarranted by the data. It might be true, but it might equally well be hopelessly parochial. We should certainly entertain the possibility that our observable patch is dramatically unrepresentative of the entire universe, and see where that leads us.
Inflation makes it plausible that our local conditions don’t stretch across the entire universe. In Alan Guth’s original scenario, inflation represented a temporary period in which the early universe was dominated by false-vacuum energy, which then went through a phase transition to convert to ordinary matter and radiation. But it was eventually realized that inflation could be eternal — unavoidable quantum fluctuations could keep inflation going in some places, even if it turns off elsewhere. In fact, even if it turns off “almost everywhere,” the tiny patches that continue to inflate will grow exponentially in volume. So the number of actual cubic centimeters in the inflating phase will grow without bound, leading to eternal inflation. Andrei Linde refers to such a picture as self-reproducing.
If inflation is eternal into the future, maybe you don’t need a Big Bang? In other words, maybe it’s eternal into the past, as well, and inflation has simply always been going on? Borde, Guth and Vilenkin proved a series of theorems purporting to argue against that possibility. More specifically, they show that a universe that has always been inflating (in the same direction) must have a singularity in the past.
But that’s okay. Most of us suffer under the vague impression — with our intuitions trained by classical general relativity and the innocent-sounding assumption that our local uniformity can be straightforwardly extrapolated across infinity — that the Big Bang singularity is a past boundary to the entire universe, one that must somehow be smoothed out to make sense of the pre-Bang universe. But the Bang isn’t all that different from future singularities, of the type we’re familiar with from black holes. We don’t really know what’s going on at black-hole singularities, either, but that doesn’t stop us from making sense of what happens from the outside. A black hole forms, settles down, Hawking-radiates, and eventually disappears entirely. Something quasi-singular goes on inside, but it’s just a passing phase, with the outside world going on its merry way.
The Big Bang could have very well been like that, but backwards in time. In other words, our observable patch of expanding universe could be some local region that has a singularity (or whatever quantum effects may resolve it) in the past, but is part of a larger space in which many past-going paths don’t hit that singularity.
The simplest way to make this work is if we are a baby universe. Like real-life babies, giving birth to universes is a painful and mysterious process. There was some early work on the idea by Farhi, Guth and Guven, as well as Fischler, Morgan and Polchinski, which has been followed up more recently by Aguirre and Johnson. The basic idea is that you have a background spacetime with small (or zero) vacuum energy, and a little sphere of high-density false vacuum. (The sphere could be constructed in your secret basement laboratory, or may just arise as a thermal fluctuation.) Now, if you’re not careful, the walls of the sphere will simply implode, leaving you with some harmless radiation. To prevent that from happening, you have two choices. One is that the size of the sphere is greater than the Hubble radius of your universe — in our case, more than ten billion light years across, so that’s not very realistic. The other is that your sphere is not simply embedded in the background, it’s connected to the rest of space by a “wormhole” geometry. Again, you could imagine making it that way through your wizardry in gravitational engineering, or you could wait for a quantum fluctuation. Truth is, we’re not very clear on how feasible such quantum fluctuations are, so there are no guarantees.
But if all those miracles occur, you’re all set. Your false-vacuum bubble can expand from a really tiny sphere to a huge inflating universe, eventually reheating and leading to something very much like the local universe we see around us today. From the outside, the walls of the bubble appear to collapse, leaving behind a black hole that will eventually evaporate away. So the baby universe, like so many callous children, is completely cut off from communication with its parent. (Perhaps “teenage universe” would be a more apt description.)
Everyone knows that I have a hidden agenda here, namely the arrow of time. The thing we are trying to explain is not “why was the early universe like that?”, but rather “why was the history of universe from one end of time to the other like that?” I would argue that any scenario that purports to explain the origin of the universe by simply invoking some special magic at early times, without explaining why they are so very different from late times, is completely sidestepping the real question. For example, while the cyclic-universe model is clever and interesting, it is about as hopeless as it is possible to be from the point of view of the arrow of time. In that model, if we knew the state of the universe to infinite precision and evolved it backwards in time using the laws of physics, we would discover that the current state (and the state at every other moment of time) is infinitely finely-tuned, to guarantee that the entropy will decrease monotonically forever into the past. That’s just asserting something, not explaining anything.
The baby-universe idea at least has the chance to give rise to a spontaneous violation of time-reversal symmetry and explain the arrow of time. If we start with empty space an evolve it forward, baby universes can (hypothetically) be born; but the same is true if we run it backwards. The increase of entropy doesn’t arise from a fine-tuning at one end of the universe’s history, it’s a natural consequence of the ability of the universe to always increase its entropy. We’re a long way from completely understanding such a picture; ultimately we’ll have to be talking about a Hilbert space of wavefunctions that involve an infinite number of disconnected components of spacetime, which has always been a tricky problem. But the increase of entropy is a fact of life, right here in front of our noses, that is telling us something deep about the universe on the very largest scales.
Update: On the same day I wrote this post, the cover story at New Scientist by David Shiga covers similar ground. Sadly, subscription-only, which is no way to run a magazine. The article also highlights the Banks-Fischler holographic cosmology proposal.
Dear Sean,
What will figuring out the big bang tell us about what is currently (within the constraints of our light cone, etc) happening in our universe?
Would it have any predictive value for currently operating physical processes?
cheers,
LL
Hi, I’m a bit confused. In most of the literature, for example in Freivogel et al
http://arxiv.org/abs/hep-th/0505232
it is assumed that the universe began by means of a Coleman-DeLuccia bubble in a dS background. As far as I know, Susskind and co continue to believe that this is the most likely way for the universe to begin. But you seem to be saying that this is not possible. Am I misinterpreting you in some way?
“In that model, if we knew the state of the universe to infinite precision and evolved it backwards in time using the laws of physics”
I’m confused. Exactly how is one supposed to do that in a quantum mechanical (i.e., statistical) paradigm, as opposed to a classical dynamics one?
Sean, you getting into pseudoscience in even asking questions like that, because whatever theory people may find for the initial conditions, it won’t be possible to test it. The best you will be able to do is to say you have a consistent ad hoc theory for how the universe began which includes qantum gravity effects.
It won’t be a potentially falsifiable theory, so it isn’t doing science, unless somehow the theory is based entirely on solid facts as input.
It reminds me of the time you claimed that the universal gravitational constant G had a value within 10% of the present day value a minute after the big bang. It turned out that claim was based on the assumption that the electromagnetic force (which resists fusion, due to Coulomb repulsion) remained static while G varied. If there is a unification of long range forces like electromagnetism and gravity, however, they’d both be likely to vary. If gravity and electromagnetism vary the same way, fusion rates won’t vary because an increased gravitational compression helping fusion will be offset by an increased Coulomb repulsion between approaching charged nuclei.
So it’s very wishy-washy to be investigating this stuff, especially when there are loads of implicit but unstated assumptions involved. Basically, it amounts to assuming something then claiming to have evidence from a calculation based on those assumed assumptions. This is what things like religion and string theorists do. It’s not very interesting because it’s really just orthodoxy.
Take Hawking’s radiation as another specific example. He implicitly assumes that there is pair production occurring in spacetime everywhere. In quantum field theory, spontaneous pair production in a steady field say of a black hole needs an electric field strength exceeding Schwinger’s limit of 1.3*10^18 v/m (equation 359 in http://arxiv.org/abs/quant-ph/0608140 or equation 8.20 in http://arxiv.org/abs/hep-th/0510040 ).
So for Hawking radiation to be possible due to one fermion in pair production near the event horizon falling into the hole while one escapes, you need the black hole to have a minimum electric charge of Q = 16*Pi*(m^4)(G^2)*(Permittivity of free space)/(c*e*h har).
In general, massive black holes will swallow up as much positive as negative charge, so they’re be neutral, there won’t be any pair production near the event horizon, and they can’t radiate. The situation where Hawking radiation can occur which is most interesting is where you treat fundamental partucles like electrons (which have the maximum charge to mass ratio of all matter) as radiating black holes. Then you have something to act as a source of the exchange radiation.
So it’s by examining assumptions and rejecting false assumptions that progress is made, not by theorizing willy-nilly with foundations consisting of quicksand (a host of unchecked speculation).
Stephen Hawking’s weightlessness has ruined my thread.
Sorry, man :/
Here’s a question for you:
Max Tegmark convinced me once that in the eternal inflation picture, you still could have infinite post-inflation-ending Universes embedded within the inflating bulk. The argument goes something like this:
The people inside the bubble Universe are going to interpret a line of simultaneity– the “t” parameter in their FRW metric– as not what might be the most natural “t” parameter in the bulk, but as the end of inflation. If inflation stops in a bubble, it’s likely to stop at one point, stop a little later at another point, etc. etc. etc., decaying smoothly away from that central point. (Where, implicitly here, I’ve chosen some sort of coordinate system to work in. I just hope I’m being clear enough.)
As long as the decay is smooth, farther out from the center of the bubble Universe there will be points where the end of inflation is delayed arbitrarily far into the future. However, because the people in the bubble Universe are defining “t=0” as the end of inflation, they will call those things arbitrarily far away in space.
In other words, given that space and time are all relative, it becomes possible to embed an infinite spatial volume within a finite spatial volume as long as eternal inflation really is eternal.
This is in the bubble universe picture, no the baby universe picture, and I haven’t even tried to think about entropy here, which of course is your main point.
The question at the end of all of this is: isn’t it possible, then, that isotropy and homogeneity can be strictly true within our Universe and still have this picture of the inflating bulk?
Of course, I don’t think I really believe that– I’m fully with you on your point that we only know that homogeneity and isotropy are good approximations to a spatial volume that must be a lot larger than our own Hubble Volume. Larger than that we haven’t really measured.
nigel–
I disagree with that.
This is not willy-nilly speculation. This is extrapolation. Granted, extrapolation is also scary, but it’s very different from willy-nilly speculation.
Suppose you have a theory that makes predictions (a) through (e). You’re able to test (a) through (d) but completely unable to test (e). If predictions (a) through (d) are all borne out, you now must take prediction (e) seriously. You don’t consider it proven, but you take it seriously because you take the theory seriously. The “default assumption” becomes that (e) is right, until we have a better theory that predicts something different.
Much (if not all) of what Sean is talking about is grounded in something that is connected to reality.
Rob, thanks for defending him.
“If predictions (a) through (d) are all borne out, you now must take prediction (e) seriously. You don’t consider it proven, but you take it seriously because you take the theory seriously. The “default assumption” becomes that (e) is right, until we have a better theory that predicts something different.”
Yes, that’s perfectly sensible, at least the way you put it. Problem is, there can be more than one theory which agrees with the facts, as in the case of Ptolemy’s earth centred universe with epicycles (150 AD), versus Aristarchus’ s solar system (250 BC).
Ptolemy’s theory was wrong, but it was made to fit observations better because more effort was put into it, and it was more popular because it seemed more sensible to people at the time. I’d no doubt that if you went up to one of Ptolemy’s students and mentioned Aristarchus’ theory, you’d be laughed at, or treated as a crank. Ptolemy in The Almagest actually ridiculed the solar system in a patronising, saying the earth would have to rotate which would make people fly off an make the clouds circle the equator at 1000 miles per hour, etc. You can’t defend the facts against this sort of thing, because those mainstream people will either take offense or just ignore you. Their idea of talking about science is talking about mainstream science, and non-mainstream ideas are boring or stupid to them. So your recipe which concludes “until we have a better theory that predicts something different” needs to explain exactly how such a better theory can be developed. Otherwise, the first idea that fits your recipe will assume a dictatorial prestige and brainwash everyone for centuries, allowing little space for alternatives to be developed to the point of being a serious challenge.
(sorry for poor my typing and proof reading above)
Wow, Sean, we’re actually in agreement, “in principle”, for the same strict reasoning, and Lumo is calling you nuts, so you must be right… 😉
I think that it is also a supportable claim that it is a mistake to assume that the observed accelerating expanding “flat” universe isn’t the eternal norm, as well. Eddington thought that the cosmological constant version of the general-relativistic field equation expressed the property that the universe was “self-gauging”, and this is also true of the self-regulating anthropic ecospheres/ecobalances that produce the goldilocks enigma across the universal board.
If the anthropic constraint means that the universe is “Darwinian”, then there is an analogous mechanism that enables it to leap/bang to higher orders of entropic efficiency, (as evidenced by the fact that we did this when we lept from apes to harness fire, and beyond…), so the second law is never violated and the arrow of time is fixed.
Of course, this advocates a NON-singular beginning to our universe, as traits or characteristics are *necessarily* “convolved” forward in a Darwinian universe.
It seems to me very simple that an inherent asymmetry in the energy of the universe will necessitate such a configuration, but again… you’ve made an assumption about the infinite nature of the universe that is not a proven fact.
So you forgot the most natural explanation, given only what we actually know.
Great post and great question.
On that question, I have a possible follow up question or two which perhaps fits the subject of the thread:
If I understand it correctly Linde presents another possible way around the Borde, Guth, Vilenkin results that could work for bubble universes as well.
Roughly, it seems he proposes that one should always be able to find “past-going paths” of the inflating bulk that goes further back than the BGV bound for a specific set of paths (perhaps only describing the local end of inflation and forward). I.e. the global BGV bound can be pushed unboundedly back, as I understand it. I’m not sure if others accepts this possibility.
So how does one think of entropy within “past-going paths” in the inflating bulk anyway? Specifically on the above, assuming it could be always expanding instead of having an initial condition within a bounded past, is it required and/or possible?
Hmm. Not a very clear formulation, I’m afraid.
First, “a specific set of paths (perhaps only describing the local end”, should be “a specific set of paths (the later perhaps only describing the local end”.
Second, “I’m not sure if others accepts this possibility.” was meant to be the first question: I’m not sure if others accepts this as a possibility?
Pingback: Reckless extrapolation at Freedom of Science
Nigel,
The problem with your argument is that fitting the model to observation is not the only criteria modern scientists use to make judments. Practically any model can be made to fit observations. However, the subset of such models which are internally consistent with known laws of physics as well as mathematical consistency is very small. Take your example of the Ptolemaic model. Sure, it fits the observational data very well, but it violates known physical laws. Thus, modern scientists would know it is wrong on this basis. String theorists and cosmologists construct models to explain the universe, however they too are tightly constrained by physics and mathematics. One of the marvels of string theory is that satisfies so many constraints coming from mathematics, quantum mechanics etc. that many people cannot believe that it doesn’t have relevance to our universe, despite the fact that string theorists cannot as of yet make firm predictions.
Blake (14)– As far as I can tell, the Bogdanovs are just charlatans who strung some cool-sounding words together. But I haven’t looked at their papers closely, so I could be wrong. Their ideas certainly haven’t affected the mainstream conversation in any substantial way. The Wikipedia sidebar is perfectly sensible, however.
Sourav (24)– All options are open, but I’m not sure why that would make the birthing any less tortuous.
NCndL (27)– I don’t think I’m saying anything is not possible, as much is up in the air in this game. Ordinarily, “Coleman-deLucia bubble) refers to tunneling from a large vacuum energy to a small one, while I’m suggesting that the inverse process is ultimately going to be more important.
agm (28)– If you know the complete state, you just use Schrodinger’s equation to evolve it in time. I’m assuming that wavefunction collapse is a perception of local observers rather than a fundamental law of physics, but that’s another debate entirely.
Rob (30)– Yes, formally speaking, you can embed an infinite open universe within a single bubble inside de Sitter. Whether that actually happens in practice is a different matter; for example, Aguirre, Johnson, and Shomer just wrote a paper about observational effects from bubbles colliding into each other. (Yet another reminder that it’s premature to indulge in self-righteous babble about what is and is not observable before we fully understand the theories we are talking about.)
“The problem with your argument is that fitting the model to observation is not the only criteria modern scientists use to make judments.” – V
I’m in favour of building theories on the basis of facts and making predictions, checking the predictions, etc. That’s science.
“Practically any model can be made to fit observations. However, the subset of such models which are internally consistent with known laws of physics as well as mathematical consistency is very small.” – V
No, the new theory has to disagree with the known laws of physics in order to get anywhere. For example, the known force laws in the standard model predict that forces don’t unify at 10^16 GeV.
If a new theory must be consistent with the old theory, the new theory is just a carbon copy and – unless it is covering an area of physics which is devoid of any existing laws (there aren’t any such empty areas of physics) – it will come into conflict with existing laws.
For example, supersymmetry predicts – contrary to the existing laws of the standard model – that electromagnetic, weak and strong force strengths unify at 10^16 GeV. That blows your argument sky high, if you think string theory is science and is consistent with existing laws.
“… Take your example of the Ptolemaic model. Sure, it fits the observational data very well, but it violates known physical laws. Thus, modern scientists would know it is wrong on this basis. …” – V
Evolving dark energy would violate conservation of energy, so you’d dismiss it out of hand for being inconsistent with known laws? Basically your argument would also ban progress in quantum gravity, since any final theory would need to be inconsistent with known physical laws in either general relativity or quantum gravity. (To start with, a modification of general relativity is needed to allow for quantum effects on the gravity constant Glike redshift over massive cosmological distances of force-mediating radiation being exchanged between distant gravitational charges, i.e. receding masses.)
If we presume that the whole universe could be compressed into a singularity
and we presume the original singularity dispersed matter, mass and gravity – after the big bang …
Then the gravity is out there (and here)
The gravity from singularities in blackholes
The gravity in galaxies (including the Milky Way)
The gravity in the Sun, Earth & Moon, …
And possibly Sean some portion is in your favourite place
However the observable universe is not the limit of the Universe, the periphery or cosmic event horizon, is the perimeter of an ‘event’ NOT OF SPACE or the Universe.
Nigel,
Your argument that SUSY would violate the know laws of physics because it predicts that the gauge couplings unify whic is in conflict with the non-SUSY standard model doesn’t make any sense to me. First, I would hardly charactize the failure of the gauge couplings to unify in nonSUSY SM as a law of physics, in particular since we do at present have the ability to check the values of the gauge couplings at 10^{16} GeV. The standard model is an effective theory, which may be extended by SUSY.
Regarding general relativity, it is also an effective field theory and does not hold ‘all the way’. However, I would expect any quantum theory of gravity to reproduce general relativity in the regime for which it is valid. I would point out that most physicists believe that quantum mechanics is something which should hold all the way and we should expect any theory to be consistent with it.
V, Supersymmetry is a good example. It modifies the existing extrapolations of three experimentally based force laws at unobservably high energy, without good reason (unless you think that unification is beautiful and a good reason), it introduces unobserved superpartners, and 6 extra dimensions. Dr Woit explains on page 177 of Not Even Wrong that using the measured weak SU(2) and electromagnetic U(1) forces, supersymmetry predicts the SU(3) force incorrectly high by 10-15%, when the experimental data is accurate to a standard deviation of about 3%.
All these things can be viewed as incompatibilities with existing knowledge. But they are excused because each is just a little difficulty as seen in isolation (just like the debtor with a million little debts of $1 each, who refused to see the big picture – and his big problem).
A question that should be answered is what happens to the electromagnetic charge energy which is “shielded” by dielectric of the Dirac sea, composed of radially polarized pairs of fermions in loops between the IR and UV cutoffs? The electric charge energy of the bare core of an electron is considerably higher than the observed (screened) value. Does the attenuated electric charge energy power short ranged forces? I.e., do the loops of W weak gauge bosons result from energy being screened by the polarized vacuum? If the attenuation of the electric charge at small distances from an electron causes the weak force, then (by analogy) you’d expect the strong force between hadrons to be caused by energy absorbed from the vacuum by radially polarized virtual electric charges at small distances. If the weak and strong forces are indeed being powered by the attenuation of the electromagnetic charge by polarized vacuum dielectric, then as you get to energies exposing the unshielded bare core charge of the electron like 10^16 GeV, the weak and strong forces should drop to zero because there’s no shielded energy to power them.
“How Did the Universe Start”?
There are many intepretations, one might just as well ask:DId the Universe start from nothing?..if so where did this nothing come from?
The nearest answer is another question:How much of the previous Universe is present in this/our Universe?
I thing the Universe came from a previous Universe, and as Einsteins GR states, you cannot create something from nothing, so there must have been a previous “something”, a little(remnant or background), of the previous Universe left_over to bounce from.
I think also that there is evidence that the Universe evolves Dimensionally, more Dimensions(late_times) evolve from less dimensions (early_times). As our Universe is still evolving, I believe that the “next” Universe will, at some point in the far of higher dimensional future, tunnel out, or phase change into the next Universe.
Seen from the next future universal generation of inhabitants, it would appear that their Universe was created from almost nothing, and it would also appear that it tunneled/emerged out of another higher dimension?
A protective process that guarantee’s evolving continuation, from low dimensional process’s,1-D,2-D,3-D, to high “extra” dimensional process can allow diemnsional tunneling to occur.
A late time higher dimensional tunnel function in this Universe, becomes a early time lower dimensional emergence in the next Universe?
Nigel,
The main motivation for introducing SUSY is that it provides a natural resolution to the gauge hierarchy problem. As an added bonus, one gets gauge coupling unification and has a natural dark matter candidate. Plus, if you make SUSY local you get supergravity. These are all very good reasons why we expect SUSY to be a feature of nature, besides mathematical beauty.
Regarding your questions about vacuum polarization, this is in fact what causes the gauge couplings to run with energy. Contrary to your idea, the electroweak interactions are a result of local gauge invariance under SU(2)_L x U(1)_Y, while the strong interactions are a result of an SU(3) local gauge invariance. The specific way in which the SU(3) gauge coupling runs with energy results in ansymptotic freedom, so that quarks are bound inside hadrons. The observation that the gauge couplings unify (if one includes SUSY) within experimental errors is support in favor of grand unification, although it does not prove it. Hopefully, a lot of our questions will be answered by LHC.
The main motivation for introducing SUSY is that it provides a natural resolution to the gauge hierarchy problem.
This is no longer strictly true. Already a couple of years ago, it was often stated that SUSY requires fine-tuning on the percent level; this was, I believe, the main motivation for split SUSY. Further null results from Tevatron, SuperKamiokande and PEDM experiments have hardly decreased the amount of fine-tuning necessary.
Anyway, we will soon know. Even in the focus point scenario, several sparticles must be available to the LHC.
The idea behind the Coleman-De Luccia instanton, discovered in 1987, is that the matter in the early universe is initially in a state known as a false vacuum. A false vacuum is a classically stable excited state which is quantum mechanically unstable. In the quantum theory, matter which is in a false vacuum may `tunnel’ to its true vacuum state. The quantum tunnelling of the matter in the early universe was described by Coleman and De Luccia. They showed that false vacuum decay proceeds via the nucleation of bubbles in the false vacuum. Inside each bubble the matter has tunnelled. Surprisingly, the interior of such a bubble is an infinite open universe in which inflation may occur. The cosmological instanton describing the creation of an open universe via this bubble nucleation is known as a Coleman-De Luccia instanton.
So what of the dark matter/energy? It this nothing?
A not very original reminder about the very idea of “universe formation”, in which for example “our universe” (implying perhaps the possibility of there being others….) somehow erupts from some sort of superspace or background: I won’t pass judgment on weird orobouros style self-looping schemes, which look fishy to me. However, if you imagine that in order for an “event” to happen, even one like the formation of a/the “universe,” then here has to be a probability of occurance within some range, even if you don’t want to call it just like time. (Otherwise, the pre-condition would just have to stay that way, wouldn’t it, unless something like “time” could operate to allow events….) Unless that background/mother reality etc. itself is confined or only existed for awhile, in which case it was created at some time-like moment, then any probability of any universe has to be played out over and over again – there can’t be just one. That doesn’t explain the principles behind the background, or prove that some universes would have different laws (i.e., ways for things to act) than others etc., or answer the modal realists’ attacks on the very idea of what “existing” means in distinguishing some possible realities from others, or the problems therof, etc. Just some background framing.