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Brief Answers to the Big Questions by Stephen Hawking

In this book, Stephen Hawking answers some of the most common and curious questions that readers want to know about.

Some of those questions include: is there a God, how did the universe begin, is time travel possible, what is inside a black hole, are there other intelligent life forms out there, and some more.

It's a great book to read because the answers come right from one of the greatest minds of our generation in a very short and easy to read format.


When we see the Earth from space, we see ourselves as a whole. We see the unity, and not the divisions. It is such a simple image with a compelling message; one planet, one human race.

While there is life, there is hope.

As a father, I will try to instill the importance of asking questions, always.

We live in a universe governed by rational laws that, through science, we can discover and understand.

I do not want to give the impression that my work is about proving or disproving the existence of God. My work is about finding a rational framework to understand the universe around us.

What are the 3 ingredients we need to cook up the universe? The 1st is matter - stuff that has mass. Matter is all around us. In the ground beneath our feet, in outer space. Dust, rock, ice, liquids. Vast clouds of gas, massive spirals of stars, each containing billions of suns, stretching away for incredible distances. The 2nd thing you need is energy. Even if you have never thought about it, we all know what energy is. Something we encounter every day. Look up at the Sun and you can feel it on your face: energy produced by a star ninety-three million miles away. The 3rd thing we need to build the universe is space. Lots of space. You can call the universe many things - awesome, beautiful, violent - but One thing you can't call it is cramped. Wherever we look we see space, more space and even more space.

The universe itself was once very small - perhaps smaller than a proton.

But of course the critical question is raised again: Did God create the quantum laws that allowed the big bang to occur? In a nutshell, do we need a God to set it up so that the big Bang could bang? I have no desire to offend anyone of faith, but I think science has a more compelling explanation than a divine creator

What caused the Sun to shine? Well, if we look inside we see the process known as fusion, in which hydrogen atoms joined to form helium, releasing vast quantities of energy in the process. Where does hygiene come from? Answer: the big Bang. The laws of nature itself tell us that not only could the universe have popped into existence without any assistance, like a proton, and have required nothing in terms of energy, but also that it is possible that nothing caused the big Bang. Nothing.

Something very wonderful happened to time at the instant of the Big Bang. Time itself began.

A typical black hole is a star so massive that it has collapsed in on itself. It is so massive that not even light can escape its gravity, which is why it is almost perfectly black. It's gravitational pull is so powerful, it warps and distorts not only light but also time. To see how, imagine a clock is being sucked into it. As the clock as closer and closer to the black hole, it begins to get slower and slower. Time itself begins to slow down. Now imagine the clock as it enters the black hole - well, assuming of course that it could withstand the extreme gravitational forces - it would actually stop. It stops not because it is broken, but because inside the black hole time itself doesn't exist. And that is exactly what happened at the start of the universe.

The question is, "Is the way the universe began chosen by God for reasons we can understand, or was it determined by a law of science?" I believe the second.

When people ask me if a God-created the universe, I tell them that the question itself makes no sense. Time didn't exist before the big Bang so there is no time for God to make the universe in. It's like asking for directions to the edge of the Earth - the Earth is a sphere that doesn't have an edge, so looking for it is a futile exercise. It is my view that the simple sex pronation is that there is no God. No one created the universe and no 1 directs our fate. This leads me to a profound realization: there is probably no heaven in after life I there. I think belief in an afterlife is just wishful thinking. There is no reliable evidence for come and it flies in the face of everything we know and science.

Stars had been raging for an infinite time, they would have heated up the universe until it reached their own temperature. Even at night, the whole sky would be as bright as the Sun, because every line of sight would have ended either on a star or in a cloud of dust that had been heated up until it was as hot as the stars. The observation that we have all made, that the sky at night is dark karma is very important. It implies that the universe could not have existed for ever, in the state we see today. Something must have happened in the past to make the stars turn on a finite time ago.

There seems to be a certain level of randomness or uncertainty in nature that cannot be removed however good our theories. It can be summed up in the uncertainty principle there was proposed in 1927 by the German scientist Werner Heisenberg. One can not accurately predict both the position and the speed of a particle. The more accurately the position as predicted the less accurately you be able to predict the speed, in a vise versa.

Because we only know some combination of position and speed of a particle, we cannot make precise predictions about the future positions and speeds of particles. We can only assign a probability to particular combinations of positions and speeds. Thus there is a certain probability to a particular future of the universe.

The universe must have many possible histories, each with its own probability. There is a history of the universe in which England wins the World Cup again, though maybe the probability is long. This idea that the universe has multiple histories may sound like science fiction, but is now accepted as science fact... Feynman's approach to understanding how things work is to assign to each possible history a particular probability, and then use this idea to make predictions.

The gravitational attraction of the extra density slows the expansion of that region, and can actually cause it to collapse to form galaxies and stars. So look carefully at the map of the microwave sky. It is the blueprint for all the structure in the universe. We are the product of quantum fluctuations in the very early universe. God really does play dice.

M-theory predicts that a great many universes were created out of nothing, corresponding to the many different possible histories. Each universe has many possible histories and many possible states as they age to the present and beyond into the future. Most of the states will be quite unlike the universe we observe.

If the density of the universe is below the critical value, gravity is too weak to stop the galaxies flying apart forever. All the stars will burn out, and the universe will get emptier and emptier, and colder and colder. So, again, things will come to an end, but in a less dramatic way. Still, we have a few billion years in hand.

We can define life as an ordered system that can keep itself going against the tendency to disorder and can reproduce itself. That is, it can make similar, but independent, ordered systems. To do these things, the system must convert energy in some ordered form - like food come the sunlight or electric power - into disordered energy, in the form of heat.

There has been some detectable change in human DNA, brought about by biological evolution, in the 10,000 years of recorded history, but the amount of knowledge handed on from generation to generation has grown enormously.

We certainly cannot continue, for long, with the exponential rate of growth of knowledge that we have had in the last 300 years. An even greater limitation and danger for future generations is that we still have the instincts, and in particular the aggressive impulses, that we had in caveman days. Aggression, in the form of subjugating or killing other men and taking their woman and food, has had definite survival advantage up to the present time period but now I could destroy the entire human race in much of the rest of life on Earth.

But we are now entering a new phase of what might be called self-designed evolution, in which we will be bale 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.

According to the theory of relativity, nothing can travel faster than light, so a round trip from us to the nearest star would take at least 8 years, and to the centre of the galaxy about 50,000 years. In science fiction, they overcome this difficulty by space warps, or travel through extra dimensions. But I don't think these will ever be possible, no matter how intelligent life becomes. IN the theory of relativity, if one can travel faster than light, one cal also travel back in time, and this would lead to problems with people going back and changing the past.

It might be possible to use genetic engineering to make DNA-based life survive indefinitely,or at least for 100,000 years. But an easier way, which is also within our capabilities already, would be to send machines. These could be designed to last long enough for interstellar travel. When they arrived at a new star, they could land on a suitable planet and mine material to produce more machine, which would be sent on to yet more stars. These machines would be a new form of life, based on mechanical and electronic components rather than macromolecules. They could eventually replace DNA-based life, just as DNA may have replaced an earlier form of life.

Thus it seems that even God is bound by the Uncertainty Principle and cannot know both the position and the speed of a particle. All the evidence points to God being an inveterate gambler, who throws the dice on every possible occasion.

In quantum mechanics, particles don't have well-defined positions and speeds Instead, they are represented by what is called a wave function. This is a number at each point of space. The size of the wave function gives the probability that the particle will be found in that position.

Do the laws governing the universe allow us to predict exactly what is going to happen to us in the future? The short answer is no, and yes. In principle, the laws allow us to predict the future. But in practice the calculations are often too difficult.

A black hole is a region where gravity is so strong that light cannot escape.

It is a very serious question. Since general relativity can permit time travel, does it allow it in our universe? and if not, why not?

Einstein showed that it would take an infinite amount of rocket power to accelerate a spaceship to beyond the speed of light. So the only way to get from one side of the galaxy to the other in a reasonable time would seem to be if we could warp space-time so much that we created a little tube or wormhole. This could connect the two sides of the galaxy and act as a short cut to get from one to the other and back while your friends were still alive.

By far the most complex systems that we have are our own bodies. Life seems to have originated in the primordial oceans that covered the Earth four billion years ago. How this happened we don't know.

Three and a half billion years ago the highly complicated molecule DNA had emerged. DNA is the basis for all life on Earth.

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