Excerpt from Chapter III (Light from the Beginning of Time) from A Universe From Nothing by Lawrence Krauss

The CMBR (cosmic microwave background radiation) is nothing less than the afterglow of the Big Bang. It provides another piece of direct evidence, in case any is needed, that the Big Bang really happened, because it allows us to look back directly and detect the nature of the very young, hot universe from which all the structures we see today later emerged.

One of the many remarkable things about the cosmic microwave background radiation is that it was discovered in New Jersey, of all places, by two scientists who really didn’t have the slightest idea what they were looking for. The other thing is that it existed virtually under all our noses for decades, potentially observable, but was missed entirely. In fact, you may be old enough [to] have seen its effects without realizing it, if you remember the days before cable television, when channels used to end their broadcast days in the wee morning hours and not run infomercials all night. When they went off the air, after showing a test pattern, the screen would revert to static. About 1 percent of that static you saw on the television screen was radiation left over from the Big Bang.

The origin of the cosmic microwave background radiation is relatively straightforward. Since the universe has a finite age (recall it is 13.72 billion years old), and as we look out at ever more distant objects, we are looking further back in time (since the light takes longer to get to us from these objects), you might imagine that if we looked out far enough, we would see the Big Bang itself. In principle this is not impossible, but in practice, between us and that early time lies a wall. Not a physical wall like the walls of the room in which I am writing this, but one that, to a great extent, has the same effect.

I cannot see past the walls in my room because they are opaque. They absorb light. Now, as I look out in the sky back further and further in time, I am looking at the universe as it was younger and younger, and also hotter and hotter, because it has been cooling ever since the Big Bang. If I look back far enough, to a time when the universe was about 300,000 years old, the temperature of the universe was about 3,000 degrees (Kelvin scale) above absolute zero. At this temperature the ambient radiation was so energetic that it was able to break apart the dominant atoms in the universe, hydrogen atoms, into their separate constituents, protons and electrons. Before this time, neutral matter did not exist. Normal matter in the universe, made of atomic nuclei and electrons, consisted of a dense “plasma” of charged particles interacting with radiation.

A plasma, however, can be opaque to radiation. The charged particles within the plasma absorb photons and reemit them so that radiation cannot easily pass through such a material uninterrupted. As a result, if I try to look back in time, I cannot see past the time when matter in the universe was last largely comprised of such a plasma.

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Excerpt from Part I, Chapter II (Characteristics of Scientific Method) from The Scientific Outlook by Bertrand Russell

“When a man tells you that he knows the exact truth about anything, you are safe in inferring that he is an inexact man. Every careful measurement in science is always given with the probable error, which is a technical term, conveying a precise meaning. It means: that amount of error which is just as likely to be greater than the actual error as to be less. It is characteristic of those matters in which something is known with exceptional accuracy that, in them, every observer admits that he is likely to be wrong, and knows about how much wrong he is likely to be. In matters where the truth is not ascertainable, no one admits that there is the slightest possibility of even the minutest error in his opinions. Who ever heard of a theologian prefacing his creed, or a politician concluding his speeches, with a statement as to the probable error in his opinions? It is an odd fact that subjective certainty is inversely proportional to objective certainty. The less reason a man has to suppose himself in the right, the more vehemently he asserts that there is no doubt whatever that he is exactly right. It is a practice of theologians to laugh at science because it changes. ‘Look at us,’ they say. ‘What we asserted at the Council of Nicea we still assert; whereas what the scientists asserted only two or three years ago is already forgotten and antiquated.’ Men who speak in this way have not grasped the great idea of successive approximations. No man who has the scientific temper asserts that what is now believed in science is exactly right; he asserts that it is a stage on the road towards the exact truth. When a change occurs in science, as, for example, from Newton’s law of gravitation to Einstein’s, what had been done is not overthrown, but is replaced by something slightly more accurate. Suppose you measured yourself with a rough apparatus, and came to the conclusion that you were 6ft. tall: you would not suppose, if you were wise, that your height was exactly 6 ft., but rather that your height was (say) between 5 ft. 11 in. and 6 ft. 1 in.; and if a very careful measurement showed that your height was (within a tenth of an inch) 5 ft. 11 9/10 in. you would not consider that that had overthrown the previous result. The previous result was that your height was about six feet , and this remains true. The case with the changes in science is precisely analogous.”

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A Streetcar Named Desire by Tennessee Williams

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