Re: Alternative

You see that's the wonder of English prose, even when it's wrong, it's write.

Re: Alternative

Alternative: another exclusive option

Alternating: changing between two or more options with some sort of pattern.

Hence, "I never wanted to grow old, but I disliked the alternative more." "The colour test consisted of alternating blocks of red, green and blue."

Dunno what the dictionary says, but that's my definition.

Re: Alternative

It's either 'alternating' or 'alternative'.

Alternate is incorrect.

Re: Alternative

Alternative?

You mean lots of leather and bad guitars?

It could be a nirvana for some, I suppose.

Re: Alternative

Well, I'veonly got my Pocket Fowler (Oxford Fowler's Modern English Usage) here with me at work, but:

p37-38:

alternate, alternative

1 Both words are adjectives and nouns and come from Latin alternus meaning 'every second' and have had closely related meanings over several centuries of use.

Fowler does say that these days alternate as a noun is much less common, though more common in American English, though alternate as a noun meaning a variant was in use in the 18c.

Garner (Garner's Modern American Usage) is also OK with 'alternate' as both noun and adjective. For use as a noun:

alternate; alternative. A. As Nouns. Alternative is needed far more often than alternate.

.

.

Alternate = (1) something that proceeds by turns with another; or (2) one that substitutes for another.

The Chicago Manual of Style recognises bothuses as well:

"alternate, adj. & n.; alternative, adj. & n. Alternate implies (1) substitute for another {we took the alternate route} or (2) taking turns with another {her alternate chaired the meeting}. Alternative implies a choice between two or more things {I prefer the second alternative}."

OK. I'll shut up now. I've probably been doing too much editing :-). I'd better stop before we get into whether it's OK to start sentences with conjunctions (er - yes. It is. According to Garner, Fowler and Chicago anyway, and that's good enough for me and my Editors :-P).

Re: Obligatory Daily Fail angle

You forgot the "...coming over here from an alternative universe and taking all our reality..." bit.

Re: Obligatory Daily Fail angle

And from the Daily Express "complete eradication of cancer predicted" and "would Diana have saved the Universe?"

And in the Sun "Lisa, 19 from Cardiff, says 'now I know that the universe is going to implode there's no point in putting my top on'"

Re: You can't bake a universe without breaking Higgs

It's quite hard to quantify that prediction, alas. Now, if you could write down a potential and make a rough, hand-waving argument as to the probabilities of this occuring -- given that we don't fully understand quantum mechanics in strong gravitational fields -- you might have a bit more chance. No Nobel prizes, though, they only go for things that are experimentally verified :( (Or politically favoured.)

Re: You can't bake a universe without breaking Higgs

Unicorns? A source of cheap filler for burgers...

Re: Vacuum state of the universe

The transition wouldn't happen everywhere at the same time, and when the transition has occurred there will be inflation within that domain, which will very effectively wipe out the structure there (and seed the fluctuations needed for a whole new universe, too). So you'd end up with our universe being slowly eaten up by these inflating (ie expanding exponentially) cancerous bubbles of lower-energy Higgs. It's like a pan being heated to boiling point -- bubbles don't seed everywhere at once, they arise spontaneously, over a finite amount of time. Of course, these bubbles then grow at a lethal rate and start smashing into each other, but that's speculative high-energy physics for you.

Re: Vacuum state of the universe

Is that anything to do with a Dyson sphere?

Re: Vacuum state of the universe

Any phase transition will do, the physics of inflation - such as they are - is sufficiently different from both the boiling and the freezing of water that neither is particularly close an analogy.

Of course it's speculative :) Inflation is a supposition, and a supposition in which the most successful models are entirely phenomenological, and the most physically-founded almost impossible to work with. By its nature, it's got to be speculative - we don't really have particle accelerators that can probe the kinds of energies it seems the universe was at back then, and we never will have.

Inflation isn't actually an ugly hack to explain the tiny size of the vacuum energy - by which I assume you mean the observed cosmological constant - with predictions from quantum mechanics (by which I assume you mean QFT). That's a separate issue, and the problem is certainly severe although not as severe as the popular "120 orders of magnitude", which is based on a hopelessly naive calculation; it's more like 40 or 50 orders of magnitude, I think, which is still pretty horrific. No, inflation doesn't have too much to do with that (you'd be thinking of quintessence or other such dark energy models, which are effectively the early stages of inflation at low energy.)

No, inflation is an ugly hack that handily sweeps away any magnetic monopoles and solves the horizon, coincidence and flatness problems while simultaneously predicting a specific primordial spectrum of perturbations ('scale-invariant', the power spectrum goes as very near to 1/k^3) -- which about 20 years later was observed in the CMB at staggering accuracy by WMAP, and in the large-scale structure by 2dF and SDSS.

Fortunately there are other ways of finding scale-invariant primordial spectra, but something whose net result *looks* like inflation seems likely to have happened. Me, I think Starobinsky was probably right; almost any high-energy modification of gravity induces leading-order corrections to the action of the form alpha R^2. That implies that, regardless what happens at even higher energies, there is a period in which the gravitational sector of the action acts as R+alpha R^2. This behaves almost exactly as a single field inflation -- so closely that it's almost, though fortunately not quite, indistinguishable -- and has a clean graceful exit. I rather feel that this is what drove the early universe inflation. I can't say that too loudly, though, since it doesn't win you too many friends on funding agencies...

Re: Vacuum state of the universe

The dodgiest thing of all is how big the Universe was supposed to be at the end of inflation - about a centimetre across. The period of inflation has to be extremely small to expand to that size while exceeding the speed of light at the moving boundary.

I get the feeling that most journalists who refer to "inflation" think of the Universe as being quite big at the time.

Re: Vacuum state of the universe

More like it had to inflate from a really small patch beforehand. You can have inflationary models with hundreds or thousands of e-foldings if you like (though you'll probably struggle to get the power spectrum right; it would be *too* scale invariant) and it wouldn't necessarily be particularly odd.

Not that there aren't plenty of dodgy things in inflation, but I'd justify them by pointing out that it's phenomenology, not fundamental physics :) (Though people - professionals - then seem to think it *is* fundamental physics. That's when I get all angry and have to go for a drink.)

Re: Vacuum state of the universe

"The freezing is the MORE apt analogy"

Fine, if you like, arguing about whether one phase transition or another in water is a better analogy for a totally different setup is as pointless as arguing about what operating system to use. For the point I was making, boiling is a perfectly apt analogy since it brings up the images of bubbles nucleating and growing.

"Reducing vacuum energy is a huge motivation for the inflation hack."

No, no it isn't. Inflation was originally generated to solve the monopole problem, which is that various GUTs around in the late 1970s predicted an abundance of magnetic monopoles, and we observe none of them. The fact that inflation also solved the horizon and the flatness problems was an enormous plus. When it was later found that chaotic inflationary models in addition predict a Harrison-Zel'dovich spectrum it more or less cemented it as the leading suggestion for events in the extremely early universe. Phenomenological, maybe, but all physics starts from phenomenology.

I'm puzzled as to why you claim the horizon problem is directly connected to the existence of the vacuum energy. The horizon problem exists even if the vacuum energy is zero. *Quintessence* is directly linked to the problem of vacuum energy, and one can certainly view quintessence as being inflationary physics applied to the recent universe.

I am aware that monopoles are not in the standard model. Indeed, it would be staggering if they were, since the electromagnetic part of the standard model is based on the electroweak theory, based on QED, based on Maxwellian electromagnetism. None of these contain monopoles. The monopole problem arose in GUTs and persists in most attempts to convincingly connect the forces together.

"FYI QFT - the Q in QFT stands for quantum...QFT is quantum mechanics when applied to fields such as, and not limited, to those of the Standard Model."

Strictly speaking, no, it isn't. Quantum mechanics is a quantised form of classical mechanics. Quantum field theory is a quantised form of classical field theory. Quantum mechanics is based on the "first" quantisation, the quantisation of a Hamiltonian. Quantum field theory is based on the "second" quantisation, the quantisation of a Lagrangian. The words "first" and "second" are a misnomer and have lead to considerable confusion, suggesting that the theories are the same, or that quantum field theory is an extended form of quantum mechanics. They're not, not really, no more than a classical theory of a point particle is the same as a classical field theory. They are obviously closely related -- they are both ultimately composed of Fock spaces and a set of commutation relations between the operators -- but they are not, strictly speaking, the same.

FYI, "FYI" is extremely irritating. If you could avoid using it it would help. Cosmology is my day job and it's nicer not to sound like I'm being patronised...

"That quantum gravity has much to say about inflation - assuming it happened - is not controversial. Is there some funding-related group-think that says that the inflaton is not related to gravity?"

Not at all. What there is is a reluctance amongst funding agencies to go beyond the current status quo, which is a phenomenological theory based on minor extensions of single-field inflation. In reality I don't think anyone actually seriously pretends that inflation is fundamental physics, but there is such an industry now built up to investigating ever more models of inflation, each predicting slightly different non-Gaussian signatures or a slightly different abundance of gravitational radiation, that sometimes I think people lose sight of that. The funding agencies, understandably enough, are currently focussing heavily on observations, the justification being that if we have the data to begin to discriminate between any of these early-universe models then we can start seeing what physics looked like, even if we're ultimately aware that we're looking at it through an emergent, phenomenological interpretation that masks the actual physics. So at the minute the money is going into CMB observation, LSS observation, and in particular to the data mining. The danger in this is that the people doing the observations and the data mining are not theorists (naturally they're not), and as a result are more inclined to take on trust what they're told by a theorist who also knows the subtleties. An example is that of gauge. On scales approaching the horizon, the very concepts of velocity, gravitational potential and density perturbation become ambiguous. An observable is unchanged, but that observable is actually nothing more than the luminosity of light from a particular point in the sky; to interpret it we need input from a model, and that input is in principle ambiguous. This hasn't mattered to observers in the past, since galaxy surveys have been in small pockets and every gauge predicts the same. It is important for future surveys, but the observers are generally unaware of this, and those that are aware have neither the time nor the training to deal with it. The impacts range from inaccurate estimates of the density to inaccurate estimates of the bias, to inaccurate estimates of the non-Gaussianity. All of these are the fundamental quantities we're wanting to measure in the first place. There are other examples like this -- the fact we can guarantee we are inaccurately applying general relativity on cosmological scales, for instance, although we don't know how large the error we're making is; or the fact that we can guarantee that perturbation theory is dead in the present universe but not *how* dead and not what impact this has on our interpretations (perhaps major, perhaps at the level of 10^{-5}; the fact that we also know general relativity is both wrong and untested on scales beyond the solar system and that modifications of gravity can provide extremely good fits to data without the need for dark matter (a complication being that most modified theories of gravity can be cast in the Einstein frame at which point they look like GR with extra dynamical scalar, vector or tensor fields); and so on -- and at the minute while there is some funding for their study there isn't anything like enough.

That went a bit off-topic, but basically the point is that there's not so much a group-think that inflation is not related to gravity, more an inertia built up that since the dominant model is of a scalar field or scalar fields propagating on a classical background, and since modifications to this are extremely speculative and unlikely to show up in the data for a long while, funding is better directed elsewhere.

""I think, which is still pretty horrific." - There's no "thinking" about it. It IS horrific when your sums are more than 1 order of mag out, let alone 40+."

We're certainly in agreement there. 40 orders of magnitude is a lot less horrific than the 120 orders of magnitude people like to quote, though. I think people quote it for the same reason that the media is getting worse and worse - it sounds nicely sensationalist. 40 orders of magnitude is bad enough but, no, we have to use a calculation that anyone who's looked at knows makes no sense, just so we can all go "ONE HUNDRED AND TWENTY ORDERS OF MAGNITUDE! OH NOES!" Pah.

Re: Vacuum state of the universe

No, a Dyson sphere is an all too real construct designed to frustrate people who just wanted to get the dust off the floor. Personally I prefer VAX, simply because it shares a name with a minicomputer that also blew a lot of hot air out of a hole round the back,

Re: Vacuum state of the universe

I've got some sympathy for funding bodies and the referee panels - they're not operating in a vacuum and they're under political pressures of their own and currently under a tight squeeze - but having missed out on quite a few grants for no reason I can tell other than "it's not yet another identikit project on inflationary non-Gaussianity or large data mining" I also do feel a bit bitter...

I think we do agree (on this ;) ) more than we disagree. I just like explaining cosmology to people - it's astounding successes as much as the deep fundamental problems that are never communicated to even the cosmologists themselves, let alone the public - so I get very carried away.

I think the 10^40 tells us that we don't understand quantum field theory well enough -- which we already knew, to be honest -- and, yes, that we simply don't understand cosmology. There is a community working on alternatives, generally on the assumption that actually Lambda=0 (though fixing that itself is a major problem without invoking some extensions to the standard model I'm no great fan of), with mixed successes. At the very least, I can categorically say that in principle the whole of modern cosmology is nothing more than an extremely successful phenomenology -- we should think of it more on the level of an emergent, effective theory rather than anything strictly physical, in the same way that thermodynamics is an emergent theory. The difference is that where we know how to derive thermodynamics from statistical mechanics, we're entirely unclear as to how we could derive cosmology (or any large gravitating system) from general relativity. Or, come to that, how to derive GR from some microscopic theory of gravity. There are hints that GR is itself intrinsically thermodynamical in nature -- the second law of thermodynamics popping up in black hole physics is the classic example -- so we'd be looking for the thermodynamics of a thermodynamical system based on an underlying system we have no knowledge of but which probably isn't Hamiltonian in nature.

It's a mess :)

Re: Vacuum state of the universe

To put the whole 120 orders of magnitude thing in context, it is worth remembering that the difference between the shortest lengh in the universe (if we accept that this is what the Planck lenth is) and the (postulated) size of the universe itself is only around 61 orders. Being out by 40 orders of magnitude is ridiculously bad, 120 orders just doesn't compute.

Re: Vacuum state of the universe

Totally right.

The number simply comes from saying "Well, the energy in momentum space is sqrt(p^2+m^2), right? Right? Well, then, we get the vacuum energy by integrating across that, right? Right? But we need a cut-off because it will go to infinity, right? Right? So what cut-off do we use to get the most idiotic answer? The Planck energy, right? Right? Right!" And then you find a number something like 123 orders of magnitude greater than the observed vacuum energy. Silliness, you can't assume there's no running towards higher energies, and you can't even apply that formula to something near the Planck energy, and you can't pretend you know what happens in the Planck regime. And if you get an infinite answer it just says that something needs renormalising, which happens throughout field theory anyway, and what we're seeing is a screened vacuum energy which quite possibly is composed of different parts anyway. (A cosmological constant is not necessarily hte same thing; if for instance gravity was well described by, I don't know, alpha * exp(R/R0), then in weak fields you'd get alpha + alpha*R/R0 in your action, and alpha would act as a vacuum energy. It would not necessarily have the sign of the vacuum energy from the matter fields so we would have cancellation of the screened constant with the gravitational constant, etc. etc.

120 orders of magnitude is absurd. Taken at face value though it doesn't half make us look like a bunch of duffers. Hell, the 40 orders of magnitude makes us look like a bunch of duffers....

Re: Vacuum state of the universe

No problem, I just like people listening to me and asking sensible questions I can answer (or saying something that totally stumps me) :)

Re: A little bubble of an ‘alternative' universe will appear and then expand out and destroy us

No, that was anti-time. Completely different bubble of death.

Re: A little bubble of an ‘alternative' universe will appear and then expand out and destroy us

S2E17 "Playing God"

While Dax mentors her first Trill initiate, a proto-universe threatens to destroy the station and Bajor.

Re: A little bubble of an ‘alternative' universe will appear and then expand out and destroy us

OK, so there are *two* bubbles of death In Star Trek. My one was the last two episodes of TNG, All Good Things. My apologies for doubting your Trekkiness.

Re: @ Change an input and “you get a different end of the universe.

Step through that door and the anomaly will be corrected...

Re: @ Change an input and “you get a different end of the universe.

Upvoted for sneaking T S Eliot into a thread on cosmology.

Perhaps there is another universe out there that consists entirely of dark matter. Then it could have begun, not with a bang, but a WIMPer.