# Penrose Altered Smolin's Thinking?

1. Jul 31, 2004

### sol2

Why the work of LQG from a SRian approach is considered?

Ths distilliation process was good for Smolin as it helped me to understand from his examples as to how the formation of the "new logic" might have extended from this head shaking that went on.

This to me lead into other issues of Quantum cryptography as well as the understanding in Glast?

2. Jul 31, 2004

### marcus

sol, the only way I can understand this post is if you are concerned by reading Lubos SPS post about Penrose. Lubos attack on Penrose presumed criticisms of String----somewhat broad-gauge I'd say----raise the topic of Penrose and the influence his thought has had on other people.

So I hear this concern in your thread title "Penrose altered Smolin's thinking?"

sol, I do not know any reason to suppose that Lubos post "Re: Penrose critique of String" has something to do with what Penrose actually said in his book.
Indeed it may not have much of anything to do with what Penrose said in book or in lecture this year (at Dublin GR17). And Penrose message may have little or nothing to do with Smolin's recent essay. It could be related but I dont know any connection.

Conceivably Lubos post was just a gratuitous attack and gives a false impression of Penrose actual position. It may be based on nothing more than information he got from the poster called "Daniel" to whom he is replying. It is not clear what the basis is.

Earlier you may remember there was a stink about Lubos attacking John Baez and seeming to quote Baez saying what Baez didnt actually say. It was a scathing personal attack which Lubos afterwards withdrew. It misled people as to what Baez had actually said---this kind of thing causes personal harm even if it is later withdrawn.

In this case Lubos does not indicate that he has read the book and he does not draw any quotes from the "Fashion Faith Fantasy" lecture. There is very little hard information.

He makes a mention of Sir Roger's "decline" which seems to refer to his age. And he talks about something Penrose said two years ago in a lecture that Lubos heard----a technical point that I think is very unlikely to be what concerns Penrose at present.

We have no evidence to suggest that Penrose actual criticism of string theory", if he made a criticism of it, has any thing to do with Smolin!
We dont know what it was, until we look at the book (which should be at the college bookstore near you), and Lubos does not know (at least he says he doesnt know in his post). So for now---sorry to say---we are just spinning our wheels and operating in a way that spreads rumors.

Let's check out the actual book "Road to Reality" and see what, if any, criticism it makes. Maybe the criticism is original and interesting!

I hope I am responding to what you are asking about. It seems like several strands of thought have gotten knotted, like a snarl that needs combing out.

3. Jul 31, 2004

### marcus

I posted a few comments on Lubos post here:
right now it just looks like Lubos post, "Re:Penrose critique of string theory" is simple animosity.

But we can just wait and see, maybe Lubos is in fact connecting with something real and Penrose has made some serious criticisms.
(I just couldnt find any evidence of that, no quotes or page references)

----------------
issue of Penrose thought as it relates to Loop Gravity!

Way back when they were just getting started Rovelli and Smolin
found they could use the "spin networks" idea of Penrose. I've forgotten when that was, around 1990 was it?

But that's ancient history and Penrose has made a whole zoo of creative mathematics which Hawking has used to do his thing, and other people have used to do their things. If Penrose is a "grandfather" of LQG well that is just because he is a general purpose grandfather of much late-20th century development.

I dont see him as partisan to LQG or biased in its favor particularly or even having had a big influence on Smolin----I guess he is stimulating company and the Loop people have benefited, along with others, with lots of conversations. But I wouldnt make a big point of the influence.

What I see now as a major impact of Penrose on LQG is something nobody has mentioned----and i could be wrong of course, very likely am wrong---which is his invoking the second law of thermodynamics to challenge Bojowald's LQC story of a bounce.

If there was a contracting phase that would have had a lot of entropy and then there was this cross-over from contraction to expansion, which takes the place of the old classical big bang singularity, and expansion begins with the gravitational field and matter density spread out rather evenly and everything very dense and hot-----and right after crossover the universe is supposed to have very low entropy.

Now entropy is supposed to increase. so at the classical bigbang ex-singularity the entropy is supposed to be the lowest it has ever been. And entropy has been increasing for 13.7 billion years till now.

In his 2nd Princeton talk, titled "Faith", Penrose challenges the bounce idea on this basis. How could you have a collapsing U with high entropy and then suddenly, after a brief quantum muddle, come out with an expanding U with very low entropy.

http://www.princeton.edu/WebMedia/lectures/
(scroll down to October 2003)

Dont take my word on this! Listen to the 2nd Princeton lecture! Or probably you can read the same argument in the book, which I havent seen yet.

My attitude is challenges to strong people (like Bojowald) are good and I think this is a serious challenge. Please correct me if you know better.
I think something interesting may come out of it.

So this, curiously enough, is how I see Penrose impact on Loop right now.
the 2nd Law is in a class of Eternal Physics, for me. And the LQC bounce---getting rid of the BB singularity---is one of the most important features of the Loop scene. And Penrose is someone who has thrown down a challenge
to this bounce, based on Eternal Physics. This is very much to my taste as a watcher. How much better can it get?

Last edited: Jul 31, 2004
4. Jul 31, 2004

### sol2

Marcus,

Do not concern yourself here.....as I am speaking from the position of Smolins book, Three Roads to Quantum Gravity. The three road he talks of, are Twistor, LQG and Strings. The SRian approach makes me realize what Penrose meant by the term quanglement. Once you see this plate you will understand I think?

What Lubos saids of others is of little consequence:) They all write lyrics to songs, but the chorus is the same. Penrose has much written, so we will have to see Lubos's comments, or books he has written? I still value his knowledge:)

I will have to look at this better.

I am keeping an open mind as well, and include strings here, because of the understanding that there, the singularity, would have been gotten rid of as well. One sees a great many gravitons collected there, and how such a cooling nature could have been gotten from the expanding nature of that blackhole(the schwarchild radius) and then its collapse( Is there no collapse?) increases this temperature in the compaction of that blackhole,as all of sudden takes place, and decreases in size, the temperature climbs.

So one has to be very flexible here in what might have been conisdering. The http://origins.colorado.edu/~ajsh/stworm.gif [Broken]? Again there are different views being expounded here, and it is hard to keep track.

I will be spending time reading those http://wc0.worldcrossing.com/WebX?14@24.DSwXcGDTres.0@.1dde6a8f/5 [Broken] you have offered. Scroll down if you click link in this sentence

Last edited by a moderator: May 1, 2017
5. Aug 20, 2004

### sol2

https://www.physicsforums.com/showpost.php?p=290547&postcount=3

Is there a pattern emerging? I think, everyone wants to know the truth?

So who are these people?

6. Aug 21, 2004

### morris

Most likely he is referring to Lee Smolin and other
"loop quantum gravity" folks at the Perimeter Institute

http://www.perimeterinstitute.ca

7. Aug 22, 2004

### sol2

The Lines still very out there in terms of who thinks who is right, and as I had said I am impressed with Smolins work with trying to understand strings in part of his summation of three roads to quantum gravity.

I would be more then interested to see Lubos attempt at a parallel approach.

8. Oct 15, 2004

### mal4mac

Penrose's "Road to Reality" is not yet available in the states but it's brewed up a storm in the UK:

He does criticise string theory, in chapter 31, "...it has achieved absolutely nothing...so far, and has little chance to play any significant role in the physics of the future." (p.887)

Last edited by a moderator: May 1, 2017
9. Oct 15, 2004

### yanniru

Before dismissing string theory ala Penrose, we might read the recent article by Gary Horowitz who claims that both strings and spacetime can be derived from Conformal Field Theory:

http://arxiv.org/abs/gr-qc/0410049
Spacetime in String Theory
Authors: Gary T. Horowitz
We give a brief overview of the nature of spacetime emerging from string theory. This is radically different from the familiar spacetime of Einstein's relativity. At a perturbative level, the spacetime metric appears as coupling constants" in a two dimensional quantum field theory. Nonperturbatively (with certain boundary conditions), spacetime is not fundamental but must be reconstructed from a holographic, dual theory.

10. Oct 19, 2004

### yanniru

Let's consider criticisms of Loop Quantum Gravity, namely criticism of Bojowald's Big Bounce theory which replaces the Big Bang.
Reference:
http://xxx.lanl.gov/abs/gr-qc/0312045
Contrasting Quantum Cosmologies
Author: D.H. Coule

For me this is a very important criticism of Loop Quantum Cosmology per Bojowald by Coule. As the critique is related to standard cosmologies and string cosmologies, it is also a review paper.

Coule criticizes several features of the LQG cosmology for the Big Bounce, which now replaces the Big Bang. However, I believe that the criticisms are actually strengths once Smolin couples Bojowald's theory to his Black Hole Universe creation hypothesis. In that case the bounce is replaced by a black hole. So lets list the criticisms:

1. Coule says the Big Bounce in unstable and permits baby universe creation. So this obviously is just what Smolin needs to describe baby universe creation in black holes.

2. Coule says that Bojowald theory predicts a reduction in entropy as the Big Bounce is approach from behind, so to speak, in time. This again is exactly what Smolin needs to counter a principal criticism of his hypothesis. If entropy did not reset to zero or something small compared to the mother universe, the result would be chaos in just a few generations. This is a definite plus for a Bojowald/Black Hole theory.

3. Coule says that the force of gravity should unify with the other forces in the Big Bounce whereas the Bojowald theory predicts that it stays relatively weak. I say that there is no reason apriori to require unification of all forces at any time in any universe. Perhaps that is just how nature works and Bojowald cosmology predicts it.

4. Coule says that the unitary condition is violated by the Bojowald theory. From my readings of Hoyle's more recent theories of a steady state universe, Hoyle now proves that matter can only be created in regions where the unitarey condition is violated. I expect that same argument applies to baby universe creation.

My interpretation of these results- Bojowald theory- is that baby universe creation bleed off energy long before unification energies are reached. I do not think that universes suffer the bounce. Dark energy considerations indicate that universes eventually expand out of existence at an accelerating rate.

Rather baby universes are created in the singularities of black holes once an energy threshold is achieved that is well below the unification energy. That threshold is where Bojowald's theory becomes non-unitary. The creation of new universes then prevents a further build up of energy in the black hole no matter how much additional mass is absorbed by the black hole.

Besides the obvious connection to Smolin's hypothesis, this result has the further implication that a theory unifying all forces up to Planck energies may not be necessary. Apparently the unified field may never happen in nature. For example, vacuum production of virtual particles can now be predicted to happen at energies well below Planck energies. And space can become nonunitary at energies well below Planck energies, or likewise at distances well above the Planck length.

For completeness the link and paper abstract are copied below:

http://xxx.lanl.gov/abs/gr-qc/0312045
Contrasting Quantum Cosmologies
Authors: D.H. Coule
We compare the recent loop quantum cosmology approach of Bojowald and co-workers with earlier quantum cosmological schemes. Because the weak-energy condition can now be violated at short distances, and not necessarily with a high energy density, a number of possible instabilities are suggested: flat space unstable to expansion or baby universe production. Or else a Machian type principle is required to prevent such behaviour. Allowing a bounce to prevent an approaching singularity seems incompatible with other standard notions concerning the arrow of time and unitarity.
Preventing rapid oscillations in the wavefunction appears in conflict with more general scalar-tensor gravity.
Other approaches such as creation from nothing'' or from some quiescent state, static or time machine, are also assessed on grounds of naturalness and fine tuning.

11. Oct 19, 2004

### marcus

yanniru, you raise quite a few interesting points in your posts
on this thread. I just wanted to say thanks. I can't respond
more than that just yet. I confess I just saw your posts (dont read
systematically and often miss things and only find them by accident)

I am glad you called attention to the paper by Coule, which I have not read and was only vaguely aware of. I will have a look at it today.

Also, dont expect any very cogent response from me in particular. I hope that several people notice that you are raising meaningful points and are moved to reply----there is kind of an unhierarchical and not entirely reliable group mind at PF that sometimes works admirably and othertimes doesnt work at all. Anyway at least one person saw your post and is going to take a look at the article your link points to.