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Three Roads to Quantum Gravity (2000)

de Lee Smolin

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"It would be hard to imagine a better guide to this difficult subject." --Scientific American In Three Roads to Quantum Gravity, Lee Smolin provides an accessible overview of the attempts to build a final "theory of everything." He explains in simple terms what scientists are talking about when they say the world is made from exotic entities such as loops, strings, and black holes and tells the fascinating stories behind these discoveries: the rivalries, epiphanies, and intrigues he witnessed firsthand. "Provocative, original, and unsettling." -The New York Review of Books "An excellent writer, a creative thinker."-Nature… (mais)
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Lay people think gravitons are massless and propagate at the speed of light.

This (as usual) is a purely dogmatic assertion based on SR. Everybody knows that the quantum phenomena violates SR. Quantum electrodynamics shows that “virtual particles” do not care for anything of old causality based physics, but are best described on the basis of chance and necessity of dialectics – two widely differing world views.

Most forces - chemical, electromagnetic, weak and strong nuclear etc., forces are supposed to be mediated by the exchange of virtual particles between mass centres; some of those virtual particles are well known. If the gravitational force is similarly due to the exchange of virtual gravitons, then there is no reason to believe that they should follow SR. If the virtual gravitons follow the limit of the speed of light, then there would be no way for these to keep the vast range of clusters and super, super clusters of galaxies in dynamic equilibrium. Local random motion of individual galaxies or other cosmic bodies would either break up and/or disallow cluster formations and we would see a uniform distribution of galaxies in the visible universe.

Look Smolin! I have had enough of your wisdom and teaching of physics to me. I thought our last encounter few weeks ago was clear enough.

It will be out of topic to talk about the infinite, and we have done so many times before. But I will try it again for the last time. I must remind you again that any causality (The “view of understanding” for Hegel) based philosophy; theology or science does not accept or believe in the infinite. Giordano Bruno was burnt on the Stake for declaring that the universe is infinite. Einstein denied any infinite universe. I quoted him before and explained why he had to assume a finite universe.

By definition infinite means something that has no limit and, is not bounded by anything else. If there are two infinites, then these two has a common boundary in between, so these are not infinite but become finites within even a bigger infinite and so on. So the “infinite hierarchies of infinities” is sheer nonsense and mysticism and I am not surprised that it “blew up the mind” of the MIT Professor. With that blown-up mind this Professor can do neither math nor science, because everything is darkened for him from that blow-up.

In mathematics you put an arbitrary origin (0) on a straight line and extend this to the right and left side to plus or minus infinities. But do you change infinity by this operation? Now I ask you if you can; to go to one end of your plus and minus infinites and come back to the origin again. If you cannot do that, then your halved infinities are also infinite and no matter how many times you divide it this will be the same! Galileo was smarter than us “scientists” when he said that addition, subtraction, expansion or compaction etc. or any other mathematical operation has no meaning for the infinite and it remains unchanged! Mathematics and physics pragmatically use the concept of infinite series for example, as a tool for approximation, calculation, measurement etc. of finite quantities and objects to certain limits, and that’s all! ( )
  antao | Aug 31, 2020 |
Not bad. This book talks about the possibilities of Quantum Gravity as a candidate to be the Unifying Theory of Physics, the Holy Grail if you will. Smolin speaks of his time as an undergraduate and as a postdoc and all of this other stuff of how the theory was developed. It borrows some things from Quantum Chromodynamics and all of that, but it isn't too bad.

I probably won't read it again, but maybe I will read more stuff by Lee Smolin. ( )
  Floyd3345 | Jun 15, 2019 |
This book provides an introduction to quantum gravity aimed at the general public. It provides three different approaches to quantum gravity, doing a decent job of discussing the strengths and weaknesses of each. The author discusses black holes and multiple universes in the journey.

His approach to each subject is historical, tracing development of key idea and briefly mentioning the people involved.

Overall the book is interesting and a rather light read. Although it is aimed at the general public, it is probably a little light for the people who would be interested in reading it. ( )
  Nodosaurus | May 25, 2015 |
I liked parts of this book, as it introduced some new ideas that I had not been exposed to. On the other hand, I miust not have been paying attention because he lost me at several crucial points and after those points, the ideas became just words on a page. I don't have the desire to re-read this to determine who was at fault.
  pbenson92025 | Sep 18, 2010 |
(cross-posted on my blog: http://davenichols.net/three-roads-quantum-gravity-lee-smolin)

I just started Smolin's latest book, The Trouble With Physics, and had gotten about 50 pages into it when my copy of Three Roads to Quantum Gravity arrived, so I decided to dig into it before moving to Trouble. Three Roads is Smolin's excellent overview of the landscape and issues involved in the pursuit of a quantum theory of gravity. A very quick read, filled with useful diagrams, I was able to knock it out in a quick evening.

Rather than giving a hundred pages of history or dozens of 'nifty' side stories, Smolin hits a few brief points needed to understand the book and quickly moves into describing how black holes, loop quantum gravity, and string theory have appeared to lead the way in the search for the elusive gravitational theory.

Smolin is one of the pioneers of loop quantum gravity, but is fairly rare in that he has also worked with string theory during his career. His perspective on the competition of the two theories offers some hope for progress by way of synergy (though of course, this was published in 2001 and the lack of a solid theory of quantum gravity, as well as the title of his latest book, The Trouble With Physics: The Rise of String Theory, the Fall of a Science, and What Comes Next, leads me to believe he has lost his rose-colored glasses).

Unlike string theory books by Brian Greene, Michio Kaku and others, and especially unlike the bitter, sarcastic (and relatively boring) anti-string theory book by Peter Woit (titled Not Even Wrong), Smolin offers a very balanced, complimentary account of physics as it stood in 2001, much of which is still accurate and pertinent today.

The discussions of casuality, black hole horizons and entropy, and the implication that space is quantized offer some well-articulated additions to the discussion of popular physics. Smolin doesn't weigh down this book with math or complex discussions of symmetry (unlike Woit). However, this book is not dumbed down for the average reader. You need some strong interest in science, and a basic understanding of physics in order to enjoy this book, but again, it isn't overwhelming or overly complex.

Later chapters cover loop quantum gravity, string theory, M-Theory (which was still extremely new at the time of publication), the holographic principle, and some meta discussions on the subject of anthropic arguments. I hope to find a more detailed presentation of loop quantum gravity, whether from Smolin or another physicist, because the discussion of the 'knots, links, and kinks' offered here is a summary and skips most of the details in favor of brevity and clarity.

I look forward now to picking up Smolin's latest book (Trouble) again and charging into a more recent offering on the subject. I'm glad I read this one before getting too far into Trouble because it really establishes the dynamics of physics as seen through Smolin's eyes as well as setting Smolin's own mindset for comparison with the latter offering. Four and one-half stars and highly recommended to the science junkie. ( )
  IslandDave | May 14, 2009 |
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"It would be hard to imagine a better guide to this difficult subject." --Scientific American In Three Roads to Quantum Gravity, Lee Smolin provides an accessible overview of the attempts to build a final "theory of everything." He explains in simple terms what scientists are talking about when they say the world is made from exotic entities such as loops, strings, and black holes and tells the fascinating stories behind these discoveries: the rivalries, epiphanies, and intrigues he witnessed firsthand. "Provocative, original, and unsettling." -The New York Review of Books "An excellent writer, a creative thinker."-Nature

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