Science has been effective at furthering our understanding of nature because the scientific ethos is based on three key principles: (1) follow the evidence wherever it leads; (2) if one has a theory, one needs to be willing to try to prove it wrong as much as one tries to prove that it is right; (3) the ultimate arbiter of truth is experiment, not the comfort one derives from one's a priori beliefs, nor the beauty or elegance one ascribes to one's theoretical models.

A universe without purpose should neither depress us nor suggest that our lives are purposeless. Through an awe-inspiring cosmic history we find ourselves on this remote planet in a remote corner of the universe, endowed with intelligence and self-awareness. We should not despair, but should humbly rejoice in making the most of these gifts, and celebrate our brief moment in the sun.

Special relativity says nothing can travel through space faster than the speed of light. But space itself can do whatever the heck it wants, at least in general relativity. And as space expands, it can carry distant objects, which are at rest in the space where they are sitting,

The Universe must be flat. Why? Well, there is two reasons. There's the one I normally say, which is: it's the only mathematically beautiful universe. Which is true, but there's another reason I don't usually... talk about but I'll talk about here. It turns out that in a flat universe the total energy of the universe is precisely zero because gravity can have negative energy. So the negative energy of gravity balances out the positive energy of matter. What's so beautiful about a universe with total energy zero? Well, only such a universe can begin from nothing, and that is remarkable because the laws of physics allow a universe to begin from nothing. You don't need a Deity. You have nothing: zero total energy, and quantum fluctuations can produce a universe. So, if the Universe isn't flat we're worried, because then you've got energy at... the very beginning of Time.

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In 5 billion years, the expansion of the universe will have progressed to the point where all other galaxies will have receded beyond detection. Indeed, they will be receding faster than the speed of light, so detection will be impossible. Future civilizations will discover science and all its laws, and never know about other galaxies or the cosmic background radiation. They will inevitably come to the wrong conclusion about the universe......We live in a special time, the only time, where we can observationally verify that we live in a special time.

It's hard to imagine a more extraordinary claim than that some hidden intelligence created a universe of more than a hundred billion galaxies, each containing more than a hundred billion stars, and then waited more than 13.7 billion years until a planet in a remote corner of a single galaxy evolved an atmosphere sufficiently oxygenated to support life, only to then reveal his existence to an assortment of violent tribal groups before disappearing again.

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I've told you two things : First, you're much more insignificant than you ever imagined and second, the future is miserable. But you should be happy, because we may live in a universe without purpose but that means the purpose in our lives is the purpose we create. And we should consider ourselves fortunate to have evolved in this place in the middle of nowhere and evolved a consciousness so we can understand the universe from the earliest moments of the big bang to the far future. So instead of being depressed, you should enjoy your brief moment in the sun.

A god who can create the laws of nature can presumably also circumvent them at will. Although why they would have been circumvented so liberally thousands of years ago, before the invention of modern communication instruments that could have recorded them, and not today, is still something to wonder about.

The amazing thing is that every atom in your body came from a star that exploded, and the atoms in your left hand probably came from a different star than your right hand. It really is the most poetic thing I know about physics. You are all stardust. You couldn’t be here if stars hadn’t exploded because the elements—the carbon, nitrogen, oxygen, iron, all the things that matter for evolution—weren’t created at the beginning of time. They were created in the nuclear furnaces of stars, and the only way they could get... into your body is if these stars were kind enough to explode. So, forget Jesus. The stars died so that you could be here today.

"A physicist, an engineer and a psychologist are called in as consultants to a dairy farm whose production has been below par. Each is given time to inspect the details of the operation before making a report.
The first to be called is the engineer, who states: "The size of the stalls for the cattle should be decreased. Efficiency could be improved if the cows were more closely packed, with a net allotment of 275 cubic feet per cow. Also, the diameter of the milking tubes should be increased by 4 percent to allow for a greater average flow rate during the milking periods."
The next to report is the psychologist, who proposes:
"The inside of the barn should be painted green. This is a more mellow color than brown and should help induce greater milk flow. Also, more trees should be planted in the fields to add diversity to the scenery for the cattle during grazing, to reduce boredom."
Finally, the physicist is called upon. He asks for a blackboard and then draws a circle. He begins: "Assume the cow is a sphere....