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Traditionally these are questions for philosophy, but philosophy is dead. Philosophy has not kept up with modern developments in science, particularly physics. Scientists have become the bearers of the torch of discovery in our quest for knowledge.
Although that account is successful enough for everyday purposes, it was found in the 1920s that this “classical” picture could not account for the seemingly bizarre behavior observed on the atomic and subatomic scales of existence. Instead it was necessary to adopt a different framework, called quantum physics.
quantum and classical physics are based on very different conceptions of physical reality.
just as there is no flat map that is a good representation of the earth’s entire surface, there is no single theory that is a good representation of observations in all situations.
While conceding that human behavior is indeed determined by the laws of nature, it also seems reasonable to conclude that the outcome is determined in such a complicated way and with so many variables as to make it impossible in practice to predict. For that one would need a knowledge of the initial state of each of the thousand trillion trillion molecules in the human body and to solve something like that number of equations. That would take a few billion years, which would be a bit late to duck when the person opposite aimed a blow.
Chaos theory
Classical science is based on the belief that there exists a real external world whose properties are definite and independent of the observer who perceives them.
In other words, if you see a herd of zebras fighting for a spot in the parking garage, it is because there really is a herd of zebras fighting for a spot in the parking garage. All other observers who look will measure the same properties, and the herd will have those properties whether anyone observes them or not. In philosophy that belief is called realism.
a particle has neither a definite position nor a definite velocity unless and until those quantities are measured by an observer.
It is therefore not correct to say that a measurement gives a certain result because the quantity being measured had that value at the time of the measurement. In fact, in some cases individual objects don’t even have an independent existence but rather exist only as part of an ensemble of many. And if a theory called the holographic principle proves correct, we and our four-dimensional world may be shadows on the boundary of a larger, five-dimensional space-time. In that case, our status in the universe is analogous to that of the goldfish.
David Hume (1711–1776), who wrote that although we have no rational grounds for believing in an objective reality, we also have no choice but to act as if it is true.
Model-dependent realism short-circuits all this argument and discussion between the realist and anti-realist schools of thought.
Our perception—and hence the observations upon which our theories are based—is not direct, but rather is shaped by a kind of lens, the interpretive structure of our human brains.
Queerer than we CAN suppose.
In vision, one’s brain receives a series of signals down the optic nerve. Those signals do not constitute the sort of image you would accept on your television.
The brain, in other words, builds a mental picture or model.
The question of whether it makes sense to say quarks really exist if you can never isolate one was a controversial issue in the years after the quark model was first proposed.
Model-dependent realism can provide a framework to discuss questions such as: If the world was created a finite time ago, what happened before that?
There seems to be no single mathematical model or theory that can describe every aspect of the universe.
In the first two thousand or so years of scientific thought, ordinary experience and intuition were the basis for theoretical explanation. As we improved our technology and expanded the range of phenomena that we could observe, we began to find nature behaving in ways that were less and less in line with our everyday experience and hence with our intuition, as evidenced by the experiment with buckyballs. That experiment is typical of the type of phenomena that cannot be encompassed by classical science but are described by what is called quantum physics.
Richard Feynman wrote that the double-slit experiment like the one we described above “contains all the mystery of quantum mechanics.”
Classical theories such as Newton’s are built upon a framework reflecting everyday experience, in which material objects have an individual existence, can be located at definite locations, follow definite paths, and so on. Quantum physics provides a framework for understanding how nature operates on atomic and subatomic scales, but as we’ll see in more detail later, it dictates a completely different conceptual schema, one in which an object’s position, path, and even its past and future are not precisely determined. Quantum theories of forces such as gravity or
the electromagnetic force are built within that framework.
Can theories built upon a framework so foreign to everyday experience also explain the events of ordinary experience that were modeled so accurately by classical physics? They can, for we and our surroundings are composite structures, made of an unimaginably large number of atoms, more atoms than there are stars in the observable universe. And though the component atoms obey the principles of quantum physics, one can show that the large assemblages that form soccer balls, turnips, and jumbo jets—and us—will indeed manage to avoid diffracting through slits. So though the components of everyday
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individual atoms and molecules operate in a manner profoundly different from that of our everyday experience. Quantum physics is a new model of reality that gives us a picture of the universe. It is a picture in which many concepts fundamental to our intuitive understanding of reality no longer have meaning.
Since this behavior is not observed on a macroscopic scale, scientists have long wondered just how large and complex something could be and still exhibit such wavelike properties.
the larger the object the less apparent and robust are the quantum effects.
To physicists, that was a startling revelation: If individual particles interfere with themselves, then the wave nature of light is the property not just of a beam or of a large collection of photons but of the individual particles.
Rather, it allows a number of different eventualities, each with a certain likelihood of being realized. It is, to paraphrase Einstein, as if God throws the dice before deciding the result of every physical process. That idea bothered Einstein, and so even though he was one of the fathers of quantum physics, he later became critical of it.
Quantum physics might seem to undermine the idea that nature is governed by laws, but that is not the case. Instead it leads us to accept a new form of determinism: Given the state of a system at some time, the laws of nature determine the probabilities of various futures and pasts rather than determining the future and past with certainty. Though that is distasteful to some, scientists must accept theories that agree with experiment, not their own preconceived notions.
For instance, we can repeat an experiment many times and confirm that the frequency of various outcomes conforms to the probabilities predicted.
Probabilities in quantum theories are different. They reflect a fundamental randomness in nature.
Feynman once wrote, “I think I can safely say that nobody understands quantum mechanics.” But quantum physics agrees with observation. It has never failed a test, and it has been tested more than any other theory in science.
It seems as if, somewhere on their journey from source to screen, the particles acquire information about both slits. That kind of behavior is drastically different from the way things seem to behave in everyday life, in which a ball would follow a path through one of the slits and be unaffected by the situation at the other.
Feynman realized one does not have to interpret that to mean that particles take no path as they travel between source and screen. It could mean instead that particles take every possible path connecting those points. This, Feynman asserted, is what makes quantum physics different from Newtonian physics.
In Feynman’s theory the mathematics and physical picture are different from that of the original formulation of quantum physics, but the predictions are the same.
In this chapter we have illustrated quantum physics employing the double-slit experiment. In what follows we will apply Feynman’s formulation of quantum mechanics to the universe as a whole. We will see that, like a particle, the universe doesn’t have just a single history, but every possible history, each with its own probability; and our observations of its current state affect its past and determine the different histories of the universe, just as the observations of the particles in the double-slit experiment affect the particles’ past. That analysis will show how the laws of nature in our
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The most incomprehensible thing about the universe is that it is comprehensible. —ALBERT EINSTEIN
For practical calculations involving the everyday world, we can continue to use classical theories, but if we wish to understand the behavior of atoms and molecules, we need a quantum version of Maxwell’s theory of electromagnetism; and if we want to understand the early universe, when all the matter and energy in the universe were squeezed into a small volume, we must have a quantum version of the theory of general relativity.
The probability, say, that the incoming electrons, with some given initial momentum, will end up flying off with some particular final momentum is then obtained by summing the contributions from each Feynman diagram. That can take some work, because, as we’ve said, there are an infinite number of them.
People have therefore sought a theory of everything that will unify the four classes into a single law that is compatible with quantum theory. This would be the holy grail of physics.
Ten dimensions might sound exciting, but they would cause real problems if you forgot where you parked your car.
String theorists are now convinced that the five different string theories and supergravity are just different approximations to a more fundamental theory, each valid in different situations.
The laws of M-theory therefore allow for different universes with different apparent laws, depending on how the internal space is curled.
It was as if a coin 1 centimeter in diameter suddenly blew up to ten million times the width of the Milky Way. That may seem to violate relativity, which dictates that nothing can move faster than light, but that speed limit does not apply to the expansion of space itself.
in 1952 Hoyle predicted that the sum of the energies of a beryllium nucleus and a helium nucleus must be almost exactly the energy of a certain quantum state of the isotope of carbon formed, a situation called a resonance, which greatly increases the rate of a nuclear reaction.
in recent years physicists began asking themselves what the universe would have been like if the laws of nature were different.
Change those rules of our universe just a bit, and the conditions for our existence disappear!
The laws of nature form a system that is extremely fine-tuned, and very little in physical law can be altered without destroying the possibility of the development of life as we know it. Were it not for a series of startling coincidences in the precise details of physical law, it seems, humans and similar life-forms would never have come into being.
What can we make of these coincidences? Luck in the precise form and nature of fundamental physical law is a different kind of luck from the luck we find in environmental factors. It cannot be so easily explained, and has far deeper physical and philosophical implications. Our universe and its laws appear to have a design that both is tailor-made to support us and, if we are to exist, leaves little room for alteration. That is not easily explained, and raises the natural question of why it is that way.
The turning point in the scientific rejection of a human-centered universe was the Copernican model of the solar system, in which the earth no longer held a central position.
We claim, however, that it is possible to answer these questions purely within the realm of science, and without invoking any divine beings.
