Thursday, March 25, 2010 ... Deutsch/Español/Related posts from blogosphere

Leonard Susskind: a 10-minute show



Leonard Susskind has created an interesting program just with himself. ;-) He talks about extra dimensions, his relations with Stephen Hawking, the landscape, the usual anthropic ideology, the lack of intelligent design, the incredibly shrinking dark energy, the mundane dark matter, string theory, its path from the nuclear scale to the Planck scale, and its uniqueness.


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reader jae said...

Shame on Lubos. You are forewarding a sermon by a believer that is stupid enough to believe that everything was created by nothing. It is faith, alone, on either side of this issue. I simply don't see why folks, especially physicists can't understand this issue. Is it ego?


reader Lumo said...

Dear jae, was your vigorous criticism of "creating everything out of nothing" supposed to be a proof of God? ;-)

If your comment had any meaningful or logical content that goes beyond these retarded emotional exclamations, then I apologize but such a hypothetical content remained thoroughly invisible.

"Creation" of everything out of nothing is how cosmology works. More generally, all complex things have evolved from simpler ones, and the very particulate mass in the Universe has evolved from pure energy such as the potential energy density of the inflaton field.

That's how science works and whenever it works in such a way that it explains a "lot" (in the present or future) while assuming a "little" (in the past), such a hypothesis is always very constrained, and if it agrees with some aspects of the observations despite the constraints, the hypothesis is consequently supported by nontrivial empirical evidence and becomes a very robust theory.

The extreme case is the "creation of everything out of nothing". Theories of this kind, when they work, are of course the most robust ones.

While Susskind would agree with me, this point was not even the point that he was trying to defend because it is obvious to every person with a rudimentary kind of scientific reasoning. Unfortunately, you manifestly don't belong to this group.


reader Lumo said...

Dear jae,

if you were referring to the energy conservation law, it doesn't really hold usefully in cosmology.

By Noether's theorem, the energy conservation law holds if the laws of physics - and the overall shape of the Universe - is time-translational-invariant.

For example, even general relativity does imply that if the spacetime is asymptotically flat, the total energy is conserved.

However, this "total energy" conservation can't be reduced to a local conservation law in general relativity. In some sense, the gravitational energy density (from waves and curvature of spacetime) always exactly cancels the other density of energy/mass, so the sum is zero.

The energy conservation law effectively becomes invalid in cosmology.

In particular, the total mass of the dust (matter with no pressure) may be preserved. But the energy of radiation - something moving by the speed of light (whose pressure is 1/3 of the energy density) - is decreasing. It's because the photons are getting longer, proportional to the linear sizes of the Universe size, and longer photons have smaller energy (inverse proportionality). So the total energy goes down as 1/R, where R are the linear distances.

On the contrary, the total energy stored by the cosmological constant or dark energy (whose pressure is minus the energy density) is increasing exponentially. It's because the energy density of this form is by definition constant - but the total volume of the Universe is exponentially increasing, being driven to accelerated expansion by the negative pressure.

The latter form of energy, whose total is exponentially increasing, dominates the Universe already today. It was also dominating the Universe during inflation although the corresponding energy density was something like 100 orders of magnitude higher than today. During inflation, the total energy of the Universe was created out of "nothing". That's how inflation works. It explains the large mass of the Universe if expressed in the fundamental (Planck) units.

There is no faith here. This is a technical field, GR has been quantitatively tested and there is no doubt that the (non)conservation of the energy works as I described. Inflation itself is "slightly" more speculative but there's strong evidence in the cosmic microwave background - and its temperature variations - supporting the statement that our Universe has gone through the inflationary era.

Cheers
LM


reader jae said...

Lubos: I don't understand much of theoretical physics, and therefore you can talk circles around me. So I give up arguing the "merits" of the case. However, I will continue to simply believe that many physicists put too little emphasis on the word, "theoretical" and far too much emphasis on castigating anyone who does not toe the atheist line.


reader Lumo said...

Dear jae,

these questions have nothing to do with faith or atheism. They're fully technical questions and they can only be answered by the actual scientific evidence.

The evidence works in such a way that in cosmology, the total mass/energy is not conserved, so in this sense, it's possible - and simple - for the Universe to create things out of nothing. One could even claim that this is a "non-atheist" or "religion-like" insight because a strict energy conservation law would historically be associated with atheism while God was thought to be able to circumvent this restriction.

At any rate, your judgments about any of these questions are totally irrational. Because you manifestly don't have any clue about physics (you don't have to tell us, everyone can see it), it would be much wiser on your side if you closed your mouth and avoided posting of further embarrassing stupidities.

Cheers
Lubos


reader Dmitri said...

I disagree on "the lack of intelligent design: huge diversity, many many possibilities of which we are only ones".
Dear Susskind, there are too many unnecessary things? "Fifth wheel" things? Indeed, supposed mankind can survive without: Saturn, the Moon, without Galileo comet, fearful asteroid Apophis, extrasolar planet 581c, war in Iraq, paralyzed Stephen. "Mankind can survive without Jews" - taught Adolf Hitler. But where man is surrounded solely by only beneficial things? It's in the mental hospital, the known room with walls of soft material. Is such patient free and loves attendants twisting him? Jesus Christ loves us, so trusted us the freedom. As free, I produced musical "Musical on LHC Large Hadron Collider safety falloff" on youtube. PS. We can not survive without paralyzed Stephen. Army does not leave its soldiers.


reader Dmitri said...

Leonard's motivation during two decades of "black hole war" with Hawking was the unacceptance of the information lost. "Information never dies", could said Leonard. But, surprisingly, Leonard answered on fora.tv, that information produced by Two Pollywogs (even their children, born inside black hole) perhaps gets lost? Just like the Hawking is saying! So, not only bodies, but also the souls of Two Pollywogs will die? Doubtful. Was there really the 2 decade compromisless battle, which is now "over"? I recommend my video, which perhaps has more rigid world-conception: "Musical on LHC Large Hadron Collider safety falloff" on youtube com. Against Leonard's theory on fora.tv. If we are - only holograms, why we are feeling the pain? The pain is very real, ask S.Hawking. Or else why the official science invented the narcosis?