đ -> Just Six Numbers - Martin Rees
Just Six Numbers : The Deep Forces That Shape The Universe
Written: 2000
Themes
Broad themes
Fine Tuning
The central theme is the delicate tuning of six key universal constants, numbers that arenât derived from universal physical laws, but have to be probed experimentally.
Will dive into more in motivations, but the author heavily ties this theme to his personal beliefs in âmeta-physicsâ. Not the traditional definition, but the one he lays out in the book: ideas of the universe that extend past our possily observable universe. Specifically, to him, a multiverse.
Scientific Progression
While not as central to the book as fine tuning, there is a lot of very interesting commentary on the progression of physics and cosmology. From Kepler to Galileo to Newton to Einstein to more modern figures (e.g. Feynman and Hawking), they all build on the shoulders of giants and leverage interesting insights and technologies to understand our universe as a whole.
Six Figures
The six figures that Martin Rees lays out are:
- The ratio between the strength of electrical forces and gravity. At small scales, electrical forces far outweigh gravity and atoms are held together and physics operates on chemical levels. If the ratio was smaller, atomic fusion would occur much sooner and the complexity of our universe would be far reduced. - It defines the energy transfer during atomic fusion. As a result of this, it determines atomic transmutation in stars and supernovas, and determine the atomic makeup of the universe. - A number measuring the amount of material in our universe. If the number were too low, the universe would expand apart with no celestial bodies. If the number were too high, the universe would have collapsed together. - The strength of universal expansion. Like the above, if it were too large the universe would have expanded apart. - A number defining the âroughnessâ of our universe. If it were smaller or zero, there would be no interesting differences between different regions of space, and the entire universe would be a consistent vacuum. If it were too large, the universe would be violent and dominated by black holes. - The dimensionality of our universe. He defines it as â3 + 1â, three spatial dimensions plus time. If were two or four, life could not exist (two dimensions is too simple for life, and four is too strict. Planetary orbits would collapse very easily with a âinverse-cubeâ law for gravity instead of our three-dimensional âinverse-squareâ law.)
Motivations
Work as a whole
Fine tuning
The author wrote this book because he sees the fine tuning that allowed a universe to develop with sufficient complexity to support intelligent life is not merely a coincidence. However, he also doesnât believe in a divine creator. Instead, he believes in the concept of multiverses that support a broad range of constants. This allows a plethora of universes that provide a sample set for us to eventually develop within a favorable one.
The book is written in order to convey how critical the six figures are to our universe, and how the universe would change if their tuning was altered. It is very convincing in showing how sensitive our universe would have been too slight disruptions to these constants, and how life would have been intractable in these âalternate universesâ. This led him to his personal belief in multiverses, as a manner of balancing both the âsampling biasâ that comes from our existence and the improbability of our existence at all.
Personal Thoughts
Enjoyment
I really enjoyed the book and learned a lot about the nature of our universe. As a computer scientist and cognitive scientist, I naturally gravitate towards admiring intelligent systems that are able to organize the flow of information. However, this leaves me oblivious to gorgeous systems in nature: the resilience of sycamore, the persistence of a weed, the glamour of a rainbow. But even with this, we see the anthrocentric bias that immediately presents itself; we canât admire what we donât know about. And I didnât know about how literal the phrase âweâre all stardustâ is, or how critical the interplay between gravity and electromagnetism is, or the scales of energy transfer in the universe (atomic fusion âonlyâ releasing 0.007 of an atoms rest mass is crazy!).
On top of that, this also put into scale the incredible scale of our universe. Weâve all heard the classic figures, like our universe being infinite or there being more stars in the sky than grains of sand on Earth. Something about this book gave me a new appreciation for it however, reading about how we are organisms, on a plant, in a solar system, in a galaxy, in a cluster/group, in aggregates. And even cooler, that we have the technology to observe all of these. The ability to visualize/appreciate our Milky Way and the nearby Andromeda, as well as groups like the Virgo Cluster, and conglomerates of these groups of galaxies forming an aggregate known as the âGreat Wallâ. And these group of group of groups of stars are ordered, and repeated through the galaxy, like the fractal patterns of mountain ridges. Itâs mind boggling to think about.
Poetically, these structures are allowed to happen both because of their attraction and repulsion. Too much attraction, and the universe would collapse into âboringâ black holes. Too little, and we wouldnât have stars or stardust for anything interesting to happen. Our universe is beautifully set up for us to have organization from scales as large as galactic cluster aggregates, to microscopic cells unaware of anything but ion gradients.
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On a more specific note, it also clarified a lot of interesting physics concepts for me:
- Folk physics vs cosmological physics. There are so many forces we would have no way of observing on Earth that fundamentally control how our universe operates. We intuitively understand inertia, and gravity, and magnetism, but what is the nucleur strong force? What is cosmic expansion? What is space-time relativity?
- WHAT nuclear fusion is (taking advantage of the strong force, a force between atomic nuclei that releases immense amounts of energy and leads to atom smashing)
- WHY stars operate on the level of nuclear fusion (incredible amounts of mass that overcome nuclear bonds)
- Dark matter. Itâs not some mysterious antimatter, but just unknown matter, dark because it doesnât lend itself to observation in any way aside from gravity.
- Cosmic expansion. Iâd always heard the universe was growing, but always visualized it as some âborders being stretched outâ, not the entire universe growing apart at the same time.
- What antimatter is (and why antimatter reactors are talked about all the time in Star Trek)
View of themes
Fine Tuning
I found a new appreciation for the rarity of our universe and the balance of forces, but his multiverse argument felt weak nonetheless.
Scientific progression
One of the coolest parts of the book, seeing how modern tech allows us to test old theories, and push forward with new ones. Also, it was thrilling seeing how the predictions made by theories aligned with other theories. The way he walked us through the different theories felt logical and decipherable even to a layman like myself. Reading the book, I didnât have to take it as fact that the universe was expanding or that there was a Big Bang, he explained WHY we believes these things and the predictions each theory makes and how accurately it holds up.
We see how our predictions about the Big Bang influence our estimates of the universal makeup of elements (deuterium prevalence for example), which allows us to test other theories, like our estimates of the amount of matter in the universe.
Scientific limitations
This might have been the coolest part for me:
- Cohort effect in astronomy - When we look into deep space, we look into the past. In the past, we might have a systematically different universe, less hydrogen and more helium for example as it gets synthesized by stars. Another reason why we might not see life in outer space, we might be observing a point in time where life couldnât possibly exist.
- Limitations in observing things at all, difficult to observe dark stuff. Rees explains how the easiest things to observe are bright objects, like stars. âDarkâ objects like planets, black holes, and dark matter have to be observed from their impacts on easier to observe objects. Their orbits, the âwobblesâ in their orbits, their overall velocity and so on.
- Reliance on being right about stuff so far: gravity, nature of stuff, understanding of mysterious particles. At the time the book was written, there were holes in their understanding of particles like neutrinos that influenced the theories that were popular at the time (for example, Rees suggests neutrinos as candidates for dark matter, despite it being refuted heavily today. This is due to more knowledge about neutrinoâs properties, like the exact quantity of its minuscule mass and overall behavior).
- Difficulty testing stuff: SUPER difficult to understand the physics pertaining to extremes: extreme gravity and extreme temperature.
- Limited experiments, and difficult to produce on Earth, or even observe elsewhere. Supernovas are rare, and expensive to record.
Quotes
There are various ways of reacting to the apparent fine tuning of our six numbers. One hard-headed response is that we couldnât exist if these numbers werenât adjusted in the appropriate âspecialâ way: we manifestly are here, so thereâs nothing to be surprised about. Many scientists take this line, but it certainly leaves me unsatisfied. Iâm impressed by a metaphor given by the Canadian philosopher John Leslie. Suppose you are facing a firing squad. Fifty marksmen take aim, but they all miss. If they hadnât all missed, you wouldnât have survived to ponder the matter. But you wouldnât just leave it at that- youâd still be baffled, and would seek some further reason for your good fortune.
- Reese, p. 164