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Alan Guth and inflation

Alan Guth of MIT is one of the nine well-deserved inaugural winners of the Milner Prize. He has received $2,999,988 because Milner failed to pay the banking fees (Alan Guth was generous enough not to have sued Yuri Milner for that so far).

As far as I know, Alan Guth is the only winner of a prize greater than the Nobel prize who has ever regularly attended a course of mine. ;-)



I have taken many pictures of Alan Guth, this is the fuzziest one but I think it's funny to see a young Italian physicist showing a finger to Alan Guth in the New York Subway during our trip to a May 2005 conference at Columbia University.

Under the name Alan H. Guth, the SPIRES database offers 73 papers, 51 of which are "citeable". That's fewer than some other famous physicists have but the advantage is that it keeps Alan Guth in the rather elite club of physicists with about 200 citations per average paper.




For quite some time, Guth would work on rather typical problems of particle physics, the science of the very small, but he of course became one of the main symbols of modern cosmology, the science of the very large. Note that the LHC probes distances comparable to \(10^{-20}\) meters while the current radius of the visible universe is about \(46\) billion light years which is \(4.4\times 10^{26}\) meters.

Every distance scale comes with its own set of physical phenomena, visible objects, and effective laws, and it may look very hard to jump over these 46 orders of magnitude from the very short distance scales to the very long distance scales and become a leader of a different scientific discipline. And indeed, it is rather hard. However, Nature recycles many physical ideas at many places so the "ideological" distance between the short and long distance scales is much shorter than the "numerical" distance indicates. Fundamental physicists are the rulers of the vast interval of distance scales (except for some messy phenomena in the middle where folks such as biologists may take over for a while).

And yes, Alan Guth's most famous discovery was a very important piece of "reconciliation" between physics of very short distances and physics of very long distances – a fascinating idea that put their friendship on firmer ground. (We're not talking about quantum gravity here which is what we do if we talk about the "stringy reconciliation"; gravity is treated classically or at most semiclassically in all the discussions about inflation.) Guth was thinking about the Higgs field – a field that became very hot this summer – and he realized it could help to solve some self-evident problems in cosmology.

By finding a speedy bridge between the world of the tiny and the world of the large, Guth has also explained where many large numbers comparing cosmology and particle physics such as "the number of elementary particles in the visible Universe" come from. These large numbers were naturally produced during an exponentially, explosively productive ancient era in the life of our Universe, an era in which the Universe acted as "the ultimate free lunch", using Guth's own words. Yes, cosmology has acquired an exemption from the energy conservation law. While people who study inflation usually say that there's nothing such as a free lunch (if they're economists, including Alan G[reenspan]), and they're "mostly" right, their colleague Alan Guth knows better.

Two papers by this author have over 1,000 citations. The pioneering 1980 paper on cosmic inflation has collected over 4,000 citations so far; Guth's 1982 paper with S.Y. \(\pi\) on fluctuations in new (i.e. non-Guth) inflation stands at 1,300+ now. Three more papers above 250 citations are about scalar fields, phase transitions, and false vacuum bubbles. All the papers are on related topics but they're inequivalent.

Old inflation: first look at the paper

Of course, I want to focus on his most famous paper whose content began to be discovered in 1979,

The Inflationary Universe: A Possible Solution to the Horizon and Flatness Problems (scanned PDF via KEK, full text)
Rotate the PDF above in the clockwise direction; these commands are available via the right click in the Chrome built-in PDF reader, too.

Some people make a breakthrough but they present the idea in a confusing way and other people have to clean the discovery. I think that Guth's paper is different. It may be immediately used in the original form. It highlights the awkward features of the old-fashioned Big Bang Theory in a very modern way, pretty much the same one that people would talk about today, 30 years later; it sketches the basic strategy how to solve them; and it lists some undesirable predictions of his model of "old inflation" that could perhaps be solved by future modifications. If you read the paper in a certain way, you might conclude that everyone else who did research on inflation was just solving some homework exercises vaguely or sharply defined by Guth. He or she was filling holes in a skeleton constructed by Alan Guth.

Problems of TBBT

If you use the term "The Big Bang Theory" in the less popular sense – i.e. if you are talking about a cosmological theory, not a CBS sitcom – you will find out that despite all the advantages, the theory has some awkward features (unlike Sheldon Cooper who doesn't have any).

Alan Guth correctly identified two main problems of TBBT: the horizon problem and the flatness problem. I am no historian and at the end of 1979, I was affiliated with a kindergarten so I can't tell you how much people were confused about the disadvantages of TBBT in the late 1970s. But it's clear that Alan Guth wasn't confused.

The horizon problem

The horizon problem is the question why the cosmic microwave background radiation discovered by Penzias and Wilson in 1964 seems to have a uniform temperature around 2.7 kelvins, with the relative accuracy of 0.001% or so, even though the places in different directions of the heaven where the photons were originally emitted couldn't possibly have communicated with each other because they were too far from each other and the speed of light is the universal cosmic speed limit (for relative speed of two information-carrying objects moving past each other).



The limitations on speed are relevant because the Penrose causal diagram of the spacetime in TBBT looks like the picture above. Observers and signals have to move along timelike or lightlike trajectories which are, by the definition of the Penrose diagram, lines on the Penrose causal diagram that are "more vertical than horizontal", i.e. at most 45 degrees away from the vertical direction.

But at the moment of the Big Bang, and this moment is depicted as the lowest horizontal "plate" on the picture, the Universe had to be created and there was no prehistory that would allow the different places of the ancient Universe to agree about a common temperature. You might object that the Universe "right after \(t=0\)" was smaller so it could have been easier to communicate (shorter distances have to be surpassed). But you also had a shorter time between \(t=0\) and the other small value of \(t\) and if you study these things quantitatively, you will realize that the latter point (shortage of time) actually becomes more important than the smallness of the distances (because the distances go like \(a\sim t^k\) for \(k\lt 1\) so they're "more constant" than the time, relatively speaking), so to agree about a common temperature, two places in the Universe would need an ever higher speed of communication which surely exceeds the speed of light \(c\).

In other words, two events at \(t=0\), the horizontal plate at the bottom of the picture, had "no common ancestors" i.e. no other events in the intersection of their past light cones – because there was no "past" before the Big Bang (sorry, Bogdanov brothers and others) – so it's puzzling why the temperature is uniform if the different regions of the Universe were "created by God" independently from others.

Alan Guth proposed a solution: if the Universe has ever been exponentially expanding for a long enough time i.e. by a high enough factor, the Penrose diagram effectively becomes much taller – it looks like we are adding a whole "pre-Big-Bang prehistory" below the bottom plate at the picture above – and suddenly there is enough room to prepare the thermal equilibrium by the exchange of heat. So with this "taller" Penrose diagram, the equal magnitude of temperature in different directions is no longer mysterious: it is a result of a relatively long period of thermalization i.e. exchange of heat that inevitably erases the temperature differences.

To successfully achieve this goal (and especially the "flatness goal" to be discussed later), we need a certain amount of time for the thermalization: the universe has to increase about\[

e^{62} \approx 10^{27}

\] times, i.e. a billion of billions of billions of times. Appreciating that \(2.718\) is a more natural base of exponentials than ten (because Nature has \(e\) and not ten fingers as humans or two fingers as the discrete physicists), physicists say that there had to be at least \(62\) \(e\)-foldings. An \(e\)-folding is a period of time during an exponential expansion in which linear distances increase \(e\) times. The required minimum varies but 60-65 is what people usually consider the minimum (but there's nothing wrong with thousands of \(e\)-foldings, either, and many models on the market actually predict even higher numbers). I only chose \(62\) so that I could have written "billion of billions of billions". ;-)

So the distances \(a\) between two places in the sky as defined by the FRW coordinates, i.e. between two "future galaxies", grew \(10^{27}\) times during inflation; the remaining multiplicative growth was due to the ordinary Big Bang Theory growth (which approximately follows power laws, \(a\sim t^k\)). But because the growth was exponential, the proper time that inflation took was just \(62\) of some basic natural units of time: a natural, small number.

You see that the exponential growth is what allows cosmology to "quickly connect" very different distance scales and time scales. If you can expand the distances \(10^{27}\) times very quickly, it's easy to inflate a subatomic object to astronomical distances within a split second. That's cool. The uniformity of the temperatures suddenly becomes much more natural (even though you could have waved your hands and say that God created different regions of the Universe in similar conditions even if they couldn't have communicated with each other – because He has some universal initial conditions that just hold everywhere).

A reader could protest that we cheated because we "explained" the unnatural features of the Universe by using large numbers that are calculated as exponentials and the exponentials themselves are "unnatural". However, the latter assertion is incorrect. The exponentials are actually totally natural in the inflationary context. It's because the FRW equations, Einstein's equations simplified for the case of a homogeneous and isotropic expanding Universe, imply that the distance \(a\) between two future (or already existing) galaxies obeys\[

\ddot a = \dots + \frac{\Lambda c^2}{3} a.

\] Einstein's equations control the second time derivative of \(a\) – which emerges from the second derivatives of the metric tensor that is hiding in the curvature tensors – and the equation for the second derivative of the distance \(a\) is analogous to an equation in the Newtonian physics, \(ma=F\), for the acceleration of an object. In the FRW case, the force on the right hand side contains a term proportional to the cosmological constant \(\Lambda\) as well as \(a\) itself. And you may verify that the equation \(\ddot a = K a\) has solutions that are exponentially increasing (or decreasing, but the increasing piece ultimately dominates unless you fine-tune the exponentially growing component exactly to zero).

Well, the exponentially increasing/decreasing functions are solutions for \(K\gt 0\) i.e. \(\Lambda\gt 0\), a positive cosmological constant. For \(K\lt 0\), the solutions are sines and cosines because the equations describe a harmonic oscillator. (That's also why a negative cosmological constant \(\Lambda\) would tend to produce a Big Crunch – a sign that the Universe would like to resemble an oscillatory one.) You may see that if you had a spring with a negative (repulsive) spring constant, it would shoot the ball attached on the spring exponentially.

It's because the derivative (and the second derivative) of the exponential function is the exponential function (times a different normalization) in general. I hope you know the joke about functions walking on the street. Suddenly, the derivative appears behind the corner. All functions are scared to hell. Only one of them is proudly marching on the sidewalk. The derivative approaches the function and asks: Why aren't you afraid of me? I am \(e^x\), the function answers and moves the derivative by one unit of distance away from itself (because the exponential of the derivative is the shift operator, because of the formula for the Taylor expansion).

Sorry if I made the joke unfunny by the more advanced Taylor expansion piece. ;-)

Fine. The exponential (the exponentially increasing proper distance between the seeds of galaxies) is a totally natural solution of the basic universal equations – of nothing else than Einstein's equations expressed in a special cosmological context. It's not cheating. It's inevitable physics.

Flatness problem

Concerning the flatness problem, I may recommend you e.g. this question on the Physics Stack Exchange plus my answer.

Einstein's equations say that the spatial slice \(t={\rm const}\) through the Universe is a flat 3D space if the average matter density is close to a calculable "critical density", or their ratio \(\Omega=1\). However, it may be derived that \(|\Omega-1|\), the (dimensionless) deviation of the density from the value that guarantees flatness, increases with time during the normal portions of TBBT (which are either radiation-dominated or, later, matter-dominated).

Observations today show that the \(t=13.7\) billion years slice is a nearly flat three-dimensional space – the curvature radius is more than 1.5 orders of magnitude longer than the radius of the visible Universe (i.e. the curvature radius is longer than hundreds of billions of light years) – so \(|\Omega-1|\leq 0.01\) or so today. But because this \(|\Omega-1|\) was increasing with time, we find out that when the Universe was just minutes or seconds old (or even younger), \(|\Omega-1|\) had to be much more tiny, something like \(10^{-{\rm dozens}}\). Such a precisely fine-tuned value of the matter density is unnatural because \(|\Omega-1|\) may a priori be anything of order one and it may depend on the region.

Our Universe today seems rather accurately flat – I mean the 3D spatial slices – and you would like to see an explanation. You would expect that the flatness is an inevitable outcome of the previous evolution. However, TBBT contradicts this explanation. In TBBT, the deviations from flatness increase with time, so when the Universe was very young, the Universe had to be even closer to exact flatness by dozens of orders of magnitude, so it had to be even more unnatural when it was young than it is today! It had to be unbelievably unnaturally flat.

Again, cosmic inflation solves the problem because it reverses the trend. During cosmic inflation, \(|\Omega-1|\) is actually decreasing with time as the Universe keeps on expanding. So a sufficiently long period of inflation is again capable of producing the Universe in an unusually "nearly precisely flat" shape and some of its exponentially great flatness may be wasted in the subsequent power-law, TBBT expansion that makes the flatness less perfect. But the accuracy with which the Universe was flat after inflation was so good that there's a lot of room for wasting.

Inflation also solves other problems. For example, it dilutes exotic topological defects such as the magnetic monopoles. If you watch TV, you must have noticed that Sheldon Cooper's discovery of the magnetic monopoles near the North Pole was an artifact of a fraudulent activity of his colleagues. It seems that the number of magnetic monopoles, cosmic strings, and other topologically nontrivial objects in the Universe around us is much lower than what a generic grand unified theory would be willing to predict. Inflation makes the Universe much larger and the density of the topological defects decreases substantially, pretty much to \(O(1)\) defects per visible Universe. It's not too surprising that none of these one or several defects moving somewhere in the visible Universe has managed to hit Sheldon Cooper's devices yet.

So Alan Guth realized that the exponentially increasing period is a very natural hypothesis about cosmology beyond (i.e. before) the ordinary Big Bang expansion which helps to explain previously unnatural features of the initial conditions required by the ordinary Big Bang expansion. He also realized that the cosmological constant needed for this exponential expansion may come from a scalar field's potential energy density \(V(\phi)\). That's where his particle physics experience turned out to be precious: it's just enough to consider the potential energy for the Higgs field \(V(h)\), realize that its positive value has the same impact on Einstein's equations as a positive cosmological constant – they're really the same thing, physically speaking, because you may simply move the cosmological constant term \(-(1/2)Rg_{\mu\nu}\) to the right hand side of Einstein's equations and include it as a part of the stress-energy tensor. And he had to rename the Higgs field to an inflaton.



Guth's original "old inflation" assumes that the inflaton sits at a higher minimum of its possible values i.e. its "configuration space" during inflation and it ultimately jumps to a different place (the place we experience today) where the cosmological constant is vastly lower.

Now, the exponential expansion had to be temporary because we know that in the most recent 13.7 billion years, the expansion wasn't exponential but it followed the laws of the Big Bang cosmology. So the state of the Universe had to jump from a place in the configuration space with a large value of \(V(\phi)\) to another place with a tiny value of \(V(\phi)\). In Guth's "old inflation", it would literally be a discontinuous jump. In a year or two, "new inflation" i.e. "slow-roll inflation" got popular and started to dominate the inflationary literature. In the new picture, the inflaton scalar field continuously rolls down the hill from a maximum/plateau (the upper inflationary-era position is no longer a local minimum of the potential in that "new inflation" picture but it isn't necessarily a catastrophe) it occupies during inflation to the minimum we experience today. When it's near the minimum, its kinetic energy is converted to oscillations of other fields, i.e. particles that become seeds of the galaxies.

The very recent 8 years in cosmology and especially in string theory have shown that "new inflation" may possibly be incompatible with string theory. The very condition of the "slow-rollness", the requirement that the inflaton rolls down (very) slowly which is needed for the inflation to last (very) long, might be incompatible with some rather general inequalities that may follow from string theory. It's the main reason that has revived the interest in the "old inflation": the transition from inflation to the post-inflationary era could have been more discontinuous than "new inflation" has assumed for decades and physicists may be forced to get back to the roots and solve the problems of "old inflation" differently than by the tools that "new inflation" had offered.



Averaged fluctuations of the CMB temperature as a function of the typical angular scale: theory agrees with experiments.

These comments rather faithfully reflect the amount of uncertainty about inflation. The observations of the cosmic microwave background made by WMAP satellite – and even more recently, the Planck spacecraft – are in excellent, detailed agreement with the theory that needs TBBT as well as the nice, flat initial conditions, as well as some initial fluctuations away from the flatness that are naturally calculable within the inflationary framework.

So the pieces probably have to be right.

However, there are many technical details – about the mass scale associated with the inflaton (it may be close to the GUT scale but it may be as low as the electroweak scale: there are even models using the newly discovered Higgs field as the driver of inflation although they need some extra unusual ingredients); about the number of inflaton scalar fields; about their detailed potential; about the question whether any quantum tunneling has occurred when the inflationary era ended; whether the scalar field should be interpreted in a more geometric way (e.g. the distance between branes, some quantity describing the evolving shape of the hidden dimensions etc.); and other things.

But it is fair to admit that I would say that exactly the general features that were discussed in Alan Guth's pioneering paper have already been empirically established. The Nobel prize is nevertheless awarded for "much more directly" observed discoveries so it's great that Yuri Milner has created the new prize in which the "theory-driven near-complete certainty" plays a much larger role than it does in Stockholm.

And that's the memo.

Previous article about the Milner Prize winners: Ashoke Sen

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reader Aran said...

Personally I much prefer the "where do flatness and uniformity come from" problems to "WTF is inflation and where did it come from" problem.


reader Luboš Motl said...

Fine but there is a conceptual difference between these two types of problems, regardless of which one you prefer. The former one is a genuine physics problem while the latter is a learning disorder. Learning disorders are subjective while physics is about objective laws of physics which is why physicists don't even talk about the latter. Instead of WTFing, they just learn it.


The question behind your learning disorder is completely irrational. You can "ask" the same thing about every concept in science. WTF is evolution and where it came from, for example. What's the difference between these two questions? Or what's the difference between "WTF is inflation and where did it come from" and "I, Aran, am a complete imbecile", for that matter?


reader Luke Lea said...

"Fundamental physicists are the rulers of the vast interval of distance scales (except for some messy phenomena in the middle where folks such as biologists may take over for a while)."

Do you suppose the physicists will ever take over the play of ideas in the human brain? Will the biologists even get there? Right now the only "effective" theory is what evolutionary biologists call "theory of mind" and the Germans used to call "verstehen."


reader Shannon said...

Does the fact that the Big Bang is a one-off event makes it unnatural ?


reader Luboš Motl said...

A very good question. I think the answer is No. First of all, we don't really know whether the Big Bang is a one-off event; in eternal inflation, "big bangs" are repeating indefinitely.


But even if we knew that, it's not unnatural because numbers such as 1 are the most natural numbers one may get. ;-) If there's a formula in the fundamental equations that determines the number of big bangs, then it's natural that the result is either infinity or a number close enough to one. ;-)


reader Paul in Boston said...

I remember hearing Guth speak at the M.I.T. Physics colloquium about inflation in about 1979. I'm quite sure that he attributed the flatness problem to Robert Dicke. I think that the horizon problem was understood by the cosmology community as well.

Guth certainly deserves the Nobel Prize now that WMAP has confirmed his ideas.


reader Haelfix said...

Hi Lubos, what paper(s) talks about string theory potentially excluding new inflation? Any good review articles?


reader Dilaton said...

Thanks Lumo for this very nice reminder about inflation and the issues it solves, this was very enjoyable to read :-)

Some time ago I read this book in German

http://www.amazon.com/The-Inflationary-Universe-Alan-Guth/dp/0201328402

It was a lot of fun with all these autobiographic notes etc but therein Alan Guth did not mention that he used to sleep during your string theory lectures neither was a nice picture of his office included :-D

What were they discussing when the younger italian physicist showed Alan Guth the finger ...?

Now a look forward to the still outstanding 7 articles about the other FPP winners ... ;-)


reader David Nataf said...

Aran,


It may take a while to convince yourself that the flatness and horizon problems are actually problems. I didn't see the problem at first, it's the sort of thing you might take a while to recognize as being a problem.


With respect to where inflation comes from, Guth didn't invent particle physics, he was applying particle physics.


Finally, inflation makes scientific predictions. Guth didn't know that the cutvature was 0 in 1980, some people were thinking it might be 0.8 because the cosmological constant was ignored. Inflation will be further tested if NASA builds the gravitational wave detector LISA.


reader Simple Astronomer said...

True story about Alan Guth. When I was in grad school,
I admitted to the graduate adviser that I was not sure if I
had what it took to be a professional scientist and that I also thought that maybe the other grad students would turnout to be better scientists. The graduate adviser told me not to worry and said that he had the very same thoughts when he was a graduate student, except for one difference. He said that there was one grad student with whom he was sure would be less successful than himself and that student was Alan Guth.


reader Aran said...

I am surprised that you can't see the extreme difference between explanatory power and supporting evidence of inflation and evolution Lubos.

One explains pretty much all life on Earth by postulating a simple mechanism and is supported by everything from laboratory experiments to fossils.

The other explains barely anything beyond the 2 problems it was invented to explain and has very little to support it.

Making up explanations is trivial, the trick is to invent ones that explain much more then they postulate.

Inventing a completely novel and utterly different state of the whole damn universe just to explain uniformity and flatness doesn't cut it. It's too much like inventing god to explain where the universe came from.


reader Aran said...

Evolution is the framework without which nothing in biology makes sense (to paraphrase T. Dobzhansky), inflation is an idea without which almost everything in physics makes as much sense as before with the sole exception of flatness and homogeneity of early universe. Still cannot see the difference? Why don't you just admit that you don't understand evolution?


reader Luboš Motl said...

Your comment is pure propaganda.


A person with the opposite bias than yours may equally say that inflation is a framework without which nothing in cosmology makes sense while evolution is just an idea trying to find a reason for the diversity of life forms, but evolution is still unnecessary to understand how any individual organism lives.


The reason why I don't admit that I don't understand evolution is that I do understand evolution - and you know it very well. I also understand inflation and I understand that you don't understand inflation and you are a giant obnoxious arrogant demagogic asshole trying to mask your stupidity, too.


reader George Christodoulides said...

very nice article


reader Shannon said...

I find it fascinating too ;-)


reader Luboš Motl said...

Hi Haelfix, try to look e.g. at


http://arxiv.org/abs/hep-th/0703071



and references and citations thereof (it's probably a wrong way to use the word "thereof" right?).


reader Luboš Motl said...

Thanks for the history lesson! It's still important that a competent theorist was able to understand those problems "from a different field", take them seriously, and find a likely explanation.


If I were on the committee of Nobel, I would probably also say Yes, it's demonstrated by WMAP and eligible for that prize, too. Still, the acoustic peaks are only "softly linked" to modes in the inflationary Universe; there isn't quite a proof of "uniqueness" of the inflationary explanation of them.


reader Luboš Motl said...

I believe in the unity of science. Brains may be studied in science and physics is the "most general" and "most scientific" perspective on all of science. At the end, whoever studies brain is really a brain scientist, whether he is a physicist is a matter of convention. So a decidable question is whether physics training is useful or will become necessary for brain sciences. I don't know. People studying brain surely have to be physicists in some sense - e.g. in the sense that they're smart enough. ;-) But how do you exactly distinguish people who study brain via physics or non-physical science? The former are surely more quantitative but one may be quantitative even if he hadn't studied physics.


reader Gene said...

Your view of inflation parallels the views of those that just don’t get quantum mechanics. They reject it because they are unwilling to actually learn it independently of their prior biases. That intellectual filter blocks all hope of understanding.


Yes, inflation seems strange, even outrageous at first but that is not a valid reason to reject it or to disparage its importance. Inflation, like QM, is not going away. I respectfully suggest that you learn more about it before expressing your preferences so strongly. Guth made a profound advance in our understanding of the world we live in. That does matter.


reader jaded said...

There may be a case for a Nobel for Guth, but I sure hope this does not happen soon. He just won a prize which is nice (perhaps too nice!) and has won various other prizes in the past, like Gruber. There a many worthy people who have not won much. And some even have much more impressive citation records than Guth (his total is only around 9000). Guth has been saying very similar things since 1980 and has given the same kind of talk thousands of times. IMHO, monomania is not necessarily a sign of true greatness. A responsible community should try to spread the wealth around!


reader Dilaton said...

Darn, now the physics SE user Anixx is heavily trolling about fundamental physics. He has started to attach a "metaphysics" tag to perfectly valid physics questions too (some of them are probably off topic) for them to become closed or deleted:

http://meta.physics.stackexchange.com/questions/1458/metaphysics-tag/1459#comment3676_1459

Sorry for the off topic, but this is very annoying; I dont wont him to jump at questions about topics the Milner Prize is targeted at. Fundamental physics questions are allowed at physics SE, darn :-(0) !!!


reader Luboš Motl said...

Well, I would sometimes use the metaphysics tag myself, but it's undoubtedly controversial. At any rate, you may want to lower the attention paid to Anixx because he or she or it is an idiot, and an irrelevant one.


I just reminded myself about his "question", namely idea that extraterrestrial life must be impossible because lightnings guarantee quantum immortality, or some combination of words like that:


http://physics.stackexchange.com/questions/7702/does-quantum-mechanics-prohibit-extraterrestrial-life


reader Dilaton said...

Thanks Lumo, you are right...

It seems I just forgot about the rule to "not feed the trolls" ... ;-).
David seems to agree with me and as always, dmckee needs to be supervised a little bit in order to prevent him from closing valid fundamental physics questions without any good reason.

I regularely have a wary eye on which questions get closed and why, by whom etc ... :-P


reader Peter said...

Sorry off topic: What is your opinion about this paper by Sabine http://arxiv.org/abs/1208.5874. Do you think is novel?


reader Luboš Motl said...

I don't know how to evaluate whether it's novel but what's more important is whether it's right or wrong and it's just wrong.


It's complete nonsense to say that one is free to adjust the commutator of a field and its time derivative, send it zero, or establish a new symmetry (a vanishing of a commutator isn't a symmetry in any sense, another completely illogical statement).


If we accept that there is a degree of freedom that looks like the metric tensor and if the low-energy effective action is given by the Ricci curvature scalar, and there's a lot of experimental evidence for this theory, the general theory of relativity, then the commutators directly and unambiguously follow from the action. The commutators aren't independent assumptions one may adjust aside from the choice of the action. The commutators *are* given by the action.


She has no clue what she's talking about.


reader Dilaton said...

The commutators or hbar are NOT fudge factors ...


reader Dilaton said...

Darn, this troll on physics SE is really obstinate :-(0)

He has posted several questions on meta to achieve the goal of his horrible attack on fundamental physics and now he is listing questions / topics to be voted off topic and closed/deleted/migrated to philosophy etc ... And David fails to efficiently stop him ... :-(((

So it is better to refrain from asking questions about topics the Milner Prize is targeted at for example over there now ...
I at least dont dare to ask about cosmology, quantum gravity, beyond the standard model physics, ST etc any more; it would just be a wast of time since this Anixx troll rules :-(

At least I still have TRF :-)


reader random said...

entry to fqxi contest is now closed, you have to dig, but there are a few nuggets in there


reader Dilaton said...

The topic of this fqxi contest seems silly to me. Why do some people so obstinately want to discard established and correct principles and foundations of physics that have not been (experimentally or theoretically) disprooved?


reader Luboš Motl said...

Right, Dilaton, and a great question.


And the likely answer is that what they find more important is to be as famous as e.g. Einstein rather than to appreciate the things for which Einstein and others are actually famous.


reader Dilaton said...

There is now a better possibility to get famous (and financially powerful):

They could do something useful and win a fundamental physics prize for example ... :-)


reader random said...

I think that's a correct observation in some cases, but I think in others it really is driven from a desire to correct misconceptions. The contest is targeted a broader audience, so it is an opportunity to communicate, whether one wins or not isn't important. I would agree with dilaton up to the point where I begin reading web posts that people are amazed that the latest results of measurements show that space cannot be discretized...and these theories came from "professional" physicists. That just tells me that it is not the laymen that are in need of help here.


reader Eugene S said...

The passage quoted by Luke Lea had been bugging me, too. Then I re-read the famous More Is Different paper by Philip Anderson.

It seems inevitable to go on uncritically to what appears at first sight to be an obvious corollary of reductionism: that if everything obeys the same fundamental laws, then the only scientists who are studying anything fundamental are those who are working on those laws. In practice, that amounts to some astrophysicists, some elementary particle physicists, some logicians and other mathematicians, and few others. ... The main fallacy in this kind of thinking is that the reductionist hypothesis does not by any means imply a "constructionist" one: The ability to reduce everything to simple fundamental laws does not imply the ability to start from those laws and reconstruct the universe.

However, with the clarification in your reply to Luke it appears that your view and Anderson's are compatible after all.


reader Luboš Motl said...

Dear Eugene, because reductionism is right, one may reduce the scientific answer to any question about well-defined ongoing phenomena or lab experiments to the fundamental laws of physics.


However, what isn't guaranteed to you by the fundamental laws of physics is that you will ask the relevant questions. What does it mean for a question to be relevant? Well, various questions about DNA are relevant even though in the space of possible bound states of atoms, they are extremely special. But they're relevant because we're surrounded by them.


So one needs to know what are the relevant questions, and some of them - those depend on our environment, our current time from the big bang, our location in the Universe and on the Earth, and the history of life and humans on Earth - won't be derivable from fundamental physics. But once you describe the environment accurately enough, everything is accessible by methods of fundamental physics.