Stephen Hawking Quotes

You cannot predict the future.

The eventual goal of science is to provide a single theory that describes the whole universe.

These lectures have shown very clearly the difference between Roger and me. He's a Platonist and I'm a positivist. He's worried that Schrödinger's cat is in a quantum state, where it is half alive and half dead. He feels that can't correspond to reality. But that doesn't bother me. I don't demand that a theory correspond to reality because I don't know what it is. Reality is not a quality you can test with litmus paper. All I'm concerned with is that the theory should predict the results of measurements. Quantum theory does this very successfully. It predicts that the result of an observation is either that the cat is alive or that it is dead. It is like you can't be slightly pregnant: you either are or you aren't.

Let us fight for every woman and every man to have the opportunity to live healthy, secure lives, full of opportunity and love. We are all time travellers, journeying together into the future. But let us work together to make that future a place we want to visit.

I have noticed even people who claim everything is predestined, and that we can do nothing to change it, look before they cross the road.

I regard the afterlife to be a fairy story for people that are afraid of the dark

Eternity is a long time, especially towards the end.

the entropy of an isolated system always increases, and that when two systems are joined together, the entropy of the combined system is greater than the sum of the entropies of the individual systems.

I have lived with the prospect of an early death for the last 49 years. I'm not afraid of death, but I'm in no hurry to die. I have so much I want to do first ... I regard the brain as a computer which will stop working when its components fail. There is no heaven or afterlife for broken down computers; that is a fairy story for people afraid of the dark.

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.

But in 1929, Edwin Hubble made the landmark observation that wherever you look, distant galaxies are moving rapidly away from us. In other words, the universe is expanding.

The matter in the universe is made out of positive energy. However, the matter is all attracting itself by gravity. Two pieces of matter that are close to each other have less energy than the same two pieces a long way apart. This is because you have to expend energy to separate them. You have to pull against the gravitational force attracting them together. Thus, in a sense, the gravitational field has negative energy. In the case of the whole universe, one can show that this negative gravitational energy exactly cancels the positive energy of the matter. So the total energy of the universe is zero.

Even if there is only one possible unified theory, it is just a set of rules and equations. What is it that breathes fire into the equations and
makes a universe for them to describe?

However, one cannot really argue with a mathematical theorem.

So Hamlet was quite right. We could be bounded in a nutshell and count ourselves kings of infinite space.