Highlights
▪ finding a rational framework to understand the universe around us.
▪ Something very wonderful happened to time at the instant of the Big Bang. Time itself began.
▪ German philosopher Immanuel Kant. He felt there were logical contradictions, or antimonies, either way. If the universe had a beginning, why did it wait an infinite time before it began? He called that the thesis. On the other hand, if the universe had existed for ever, why did it take an infinite time to reach the present stage? He called that the antithesis. Both the thesis and the antithesis depended on Kant’s assumption, along with almost everyone else, that time was absolute.
▪ Feynman’s approach to understanding how things works is to assign to each possible history a particular probability, and then use this idea to make predictions
▪ Feynman’s approach to understanding how things works is to assign to each possible history a particular probability, and then use this idea to make predictions
▪ If the boundary condition of the universe is that it has no boundary in imaginary time, it won’t have just a single history.
▪ Why is the universe the way it is?” is a restriction on the history we live in. It implies it is one of the minority of histories that have galaxies and stars. This is an example of what is called the Anthropic Principle.
▪ M-theory, which is our best candidate for a complete unified theory, allows a very large number of possible histories for the universe
▪ We are the product of quantum fluctuations in the very early universe. God really does play dice.
▪ matter of common experience that things get more disordered and chaotic with time. This observation even has its own law, the so-called second law of thermodynamics
▪ matter of common experience that things get more disordered and chaotic with time. This observation even has its own law, the so-called second law of thermodynamics
▪ whether viruses should count as life, because they are parasites, and cannot exist independently of their hosts.
▪ carbon atoms should exist at all, with the properties that they have, requires a fine adjustment of physical constants, such as the QCD scale, the electric charge and even the dimension of space–time. If these constants had significantly different values, either the nucleus of the carbon atom would not be stable or the electrons would collapse in on the nucleus.
▪ There was no carbon when the universe began in the Big Bang, about 13.8 billion years ago. It was so hot that all the matter would have been in the form of particles called protons and neutrons.
▪ no heavier elements, like carbon or oxygen, would have been formed in the early universe.
▪ some of the stars exploded as supernovae and scattered the heavy elements back into space, to form the raw material for later generations of stars.
▪ there are two techniques that have enabled us to discover planets around other stars. The first is to look at the star and see if the amount of light coming from it is constant. If a planet moves in front of the star, the light from the star will be slightly obscured. The star will dim a little bit. If this happens regularly, it is because a planet’s orbit is taking it in front of the star repeatedly.
▪ Earth was formed largely out of the heavier elements, including carbon and oxygen. Somehow, some of these atoms came to be arranged in the form of molecules of DNA. This has the famous double-helix form,
▪ Linking the two chains in the helix are pairs of nitrogenous bases. There are four types of nitrogenous bases—adenine, cytosine, guanine and thymine. An adenine on one chain is always matched with a thymine on the other chain, and a guanine with a cytosine. Thus the sequence of nitrogenous bases on one chain defines a unique, complementary sequence on the other chain. The two chains can then separate and each acts as a template to build further chains. Thus DNA molecules can reproduce the genetic information coded in their sequences of nitrogenous bases. Sections of the sequence can also be used to make proteins and other chemicals, which can carry out the instructions, coded in the sequence, and assemble the raw material for DNA to reproduce itself.
▪ RNA is like DNA, but rather simpler, and without the double-helix structure. Short lengths of RNA could reproduce themselves like DNA, and might eventually build up to DNA.
▪ DNA in a human egg or sperm contains about three billion base pairs of nitrogenous bases. However, much of the information coded in this sequence seems to be redundant or is inactive. So the total amount of useful information in our genes is probably something like a hundred million bits.
▪ nuclear war is still the most immediate danger, but there are others, such as the release of a genetically engineered virus. Or the greenhouse effect becoming unstable.
▪ There is no time to wait for Darwinian evolution to make us more intelligent and better natured. But we are now entering a new phase of what might be called self-designed evolution, in which we will be able to change and improve our DNA. We have now mapped DNA, which means we have read “the book of life,” so we can start writing in corrections. At first, these changes will be confined to the repair of genetic defects—like cystic fibrosis and muscular dystrophy, which are controlled by single genes and so are fairly easy to identify and correct. Other qualities, such as intelligence, are probably controlled by a large number of genes, and it will be much more difficult to find them and work out the relations between them. Nevertheless, I am sure that during this century people will discover how to modify both intelligence and instincts like aggression.
▪ some people won’t be able to resist the temptation to improve human characteristics, such as size of memory, resistance to disease and length of life. Once such superhumans appear, there are going to be major political problems with the unimproved humans, who won’t be able to compete. Presumably, they will die out, or become unimportant. Instead, there will be a race of self-designing beings, who are improving themselves at an ever-increasing rate.
▪ you couldn’t measure simultaneously both the position and speed of a particle exactly. To see where a particle is, one has to shine light on it. But by Planck’s work one can’t use an arbitrarily small amount of light. One has to use at least one quantum. This will disturb the particle and change its speed in a way that can’t be predicted. To measure the position of the particle accurately, you will have to use light of short wavelength, like ultra-violet, X-rays or gamma rays. But again, by Planck’s work, quanta of these forms of light have higher energies than those of visible light. So they will disturb the speed of the particle more. It is a no-win situation
▪ there could be stars that were much more massive than the Sun which had escape velocities greater than the speed of light. We would not be able to see them, because any light they sent out would be dragged back by gravity. Thus they would be what Michell called dark stars, what we now call black holes.
▪ When a black hole is created by gravitational collapse, it rapidly settles down to a stationary state, which is characterised by three parameters: the mass, the angular momentum and the electric charge.
▪ member of the pair of particles that falls into the black hole, the antiparticle say, as being really a particle that is travelling backwards in time. Thus the antiparticle falling into the black hole can be regarded as a particle coming out of the black hole but travelling backwards in time.
▪ mountain-sized black hole would give off X-rays and gamma rays, at a rate of about ten million megawatts, enough to power the world’s electricity supply. It wouldn’t be easy, however, to harness a mini black hole. You couldn’t keep it in a power station because it would drop through the floor and end up at the centre of the Earth. If we had such a black hole, about the only way to keep hold of it would be to have it in orbit around the Earth.
▪ one can think of space and time together as a four-dimensional entity called space–time. Each point of space–time is labelled by four numbers that specify its position in space and in time
▪ idea is that seven of these eleven dimensions are curled up into a space so small that we don’t notice them. On the other hand the remaining four directions are fairly flat and are what we call space–time
▪ In most cases the mistakes in copying would have made the DNA unable to reproduce itself. Such genetic errors, or mutations as they are called, would die out. But in a few cases the error or mutation would increase the chances of the DNA surviving and reproducing. Thus the information content in the sequence of nitrogenous bases would gradually evolve and increase in complexity. This natural selection of mutations was first proposed by another Cambridge man, Charles Darwin
▪ expect complexity to increase at a rapid rate, in both the biological and the electronic spheres. Not much of this will happen in the next hundred years, which is all we can reliably predict. But by the end of the next millennium, if we get there, the change will be fundamental.
▪ A laser with a gigawatt of power would provide only a few newtons of thrust. But the nanocraft compensate for this by having a mass of only a few grams. The engineering challenges are immense. The nanocraft must survive extreme acceleration, cold, vacuum and protons, as well as collisions with junk such as space dust. In addition, focusing a set of lasers totalling 100 gigawatts on the solar sails will be difficult due to atmospheric turbulence. How do we combine hundreds of lasers through the motion of the atmosphere, how do we propel the nanocraft without incinerating them and how do we aim them in the right direction?
▪ engineering problems, and engineers’ challenges tend, eventually, to be solved.
▪ As development in these areas and others moves from laboratory research to economically valuable technologies, a virtuous cycle evolves, whereby even small improvements in performance are worth large sums of money, prompting further and greater investments in research.
▪ As development in these areas and others moves from laboratory research to economically valuable technologies, a virtuous cycle evolves, whereby even small improvements in performance are worth large sums of money, prompting further and greater investments in research.
▪ Because of the great potential of AI, it is important to research how to reap its benefits while avoiding potential pitfalls. Success in creating AI would be the biggest event in human history.
▪ One can imagine such technology outsmarting financial markets, out-inventing human researchers, out-manipulating human leaders and potentially subduing us with weapons we cannot even understand.
▪ We have two options for the future of humanity as I see it: first, the exploration of space for alternative planets on which to live, and second, the positive use of artificial intelligence to improve our world.
▪ They need to be scientifically literate, and inspired to engage with developments in science and technology in order to learn more.