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Kindle Notes & Highlights
by
Lee Smolin
Read between
August 31 - October 1, 2019
For more than two centuries, until the present period, our understanding of the laws of nature expanded rapidly. But today, despite our best efforts, what we know for certain about these laws is no more than what we knew back in the 1970s.
the myriad phenomena in nature are governed by just four forces: electromagnetism, gravity, the strong nuclear force (which holds atomic nuclei together), and the weak nuclear force (responsible for radioactive decay).
Astronomers also had evidence that the universe contains a lot of dark matter—that is, matter in a form that neither emits nor reflects light.
we have no idea why neutrinos (or any of the other particles) have mass or what explains their mass value. As for the dark energy, it’s not explained in terms of any existing theory.
no new particle has been discovered, no new force found, no new phenomenon encountered that was not known and understood twenty-five years ago.
What we have, in fact, is not a theory at all but a large collection of approximate calculations, together with a web of conjectures that, if true, point to the existence of a theory.
If a large number of people have worked on a question for many years and the answer remains unknown, it may mean that the answer is not easy or obvious. Or this may be a question that has no answer.
the debate that took place a few years ago between scientists and “social constructivists,” a group of humanities and social science professors, over how science works.
We do research because even the smartest among us doesn’t know the answer.
In the United States, theorists who pursue approaches to fundamental physics other than string theory have almost no career opportunities.
we have to again confront deep questions about space and time, quantum theory, and cosmology. We again need the kinds of people who can invent new solutions to long-standing foundational problems.
Physics has always seemed to its practitioners to be almost complete.
If infinities are signs of missing unification, a unified theory will have none. It will be what we call a finite theory, a theory that answers every question in terms of sensible, finite numbers.
Quantum theory contains within it some apparent conceptual paradoxes that even after eighty years remain unresolved.
We are accidental descendants of an ancient primate, who appeared only very recently in the history of the world. It cannot be that reality depends on our existence.
We have no idea why these numbers have the values they do; we simply determine them by experiments and then plug in the numbers.
This strange new energy, which we have postulated to fit the data, is called the dark energy.
Recent measurements reveal a universe consisting mostly of the unknown.
Only 4 percent is ordinary matter. So less than 1 part in 20 is made out of matter we have observed experimentally or described in the standard model of particle physics. Of the other 96 percent, apart from the properties just mentioned, we know absolutely nothing.
Biology before Darwin and biology afterward are hardly the same science.
members of a Bible college on the way back from a mission to Africa, one purpose of which, it turned out, had been to test some of the tenets of creationism. As they sought to engage me in discussion, I warned them that they would lose, as I knew the evidence pretty well.
But one proposal for unification may end up explaining far more than the others, and it is usually the simplest.
This unified theory explained the diameters of the orbits of the planets, something no theory had done before. It was mathematically beautiful. So why wasn’t it believed?
Could there have been a more beautiful unification than the aether theory? Not only were light, electricity, and magnetism unified, their unification was unified with matter.
He meditated on the puzzle for ten years, beginning at the age of 16, and finally, in 1905, realized that the resolution required a complete revision of our understanding of space and time.
the mechanists already had the right equations, they just had the wrong interpretations.
By the time most physicists had caught up with him and accepted the special theory of relativity, Einstein was already moving far beyond it.
Hence, by telling which trajectories are accelerated and which are not, the geometry of spacetime describes the effects of gravity. The geometry of spacetime is therefore the gravitational field.
There was Nordström’s elegant unification of gravity with electromagnetism by the simple postulation of an extra, hidden dimension of space. And there was Einstein’s general theory of relativity.
the choice between the two profoundly different directions for unification was made in the only way it could have been—by experiment.
We have a name for theories of physics that rely on such an absolute, fixed framework: We call them background-dependent theories.
Make note of the distinction between background-dependent and background-independent theories. The story that unfolds over the course of this book turns on the difference between them.
Einstein didn’t believe Weyl’s theory, but he admired it, writing to Weyl, “Apart from the [lack of] agreement with reality it is in any case a superb intellectual performance.”
By the 1940s, Einstein and the few others who still pursued a unified-field theory were mostly laughed at.
Ignoring gravity meant taking a step backward, to the understanding of space and time before Einstein’s general theory of relativity.
the old trick that the laws governing the parts are often simpler than those governing the whole—and
Put simply, a symmetry is an operation that doesn’t change how something behaves relative to the outside world.
Much of the structure of the world, both social and physical, is a consequence of the requirement that the world, in its actuality, break symmetries present in the space of possibilities.
The laws describe only the space of what possibly may happen; the actual world governed by those laws involves a choice of one realization from many possibilities.
The discovery that all three forces are expressions of a single unifying principle—the gauge principle—is the deepest accomplishment of theoretical particle physics to date.
The hope was that unification would account for the values of the constants in the standard model. Instead, grand unification, if valid, introduces new constants that must be tuned by hand to hide effects that would disagree with experiment.
THE FAILURE OF the first grand unified theories gave rise to a crisis in science that continues to this day.
since the end of the 1970s there has not been a single genuine breakthrough in our understanding of elementary-particle physics.
Soviet scientists were only rarely allowed to travel, and they were discouraged from publishing in non-Soviet journals. Most Western physicists did not read the translations of Soviet journals, so there were several discoveries made in the U.S.S.R. that went unappreciated in the West.
Not only are there squarks and sleptons and photinos, there are also sneutrinos to partner the neutrinos, Higgsinos with the Higgs, and gravitinos to go with the gravitons. Two by two, a regular Noah’s ark of particles. Sooner or later, tangled in the web of new snames and naminos, you begin to feel like Sbozo the clown. Or Bozo the clownino. Or swhatever.
To invent a whole new world of the unknown and then make a theory with many parameters—parameters that can be tuned to hide all the new stuff—is not very impressive, even if it’s technically challenging to pull off.
To try to solve any of the other problems without solving this one would be like trying to negotiate a contract in a country without law.
Space and time emerge from the laws rather than providing an arena in which things happen.
How it came to be that the highest achievement of the most famous scientist of the twentieth century has been virtually ignored by most of those clamoring to follow in his footsteps is one of the strangest stories in the history of science.
By now almost everyone who thinks seriously about quantum gravity agrees with Bronstein, but it has taken seventy years.
