Brief Answers To The Big Questions-Part 1

Impression:

I am writing about the first 5 of the Big Questions Stephen Hawking wrote about in “Brief Answers To The Big Questions.” He thinks it is really important for us to think about the Big Questions. The holy grail of physics is to come up with a theory that explains everything. We cannot hope to come up with one if we are not thinking about the big questions.

Hawking did not believe in God. He puts forth the notion that the universe does not need God to exist in the state that it does exist. I am personally more inclined to believe in a God; I think spirituality is separate from science.

How did it all begin?

For so long, people believed that the universe had existed forever. This idea is apparent in Plato’s world of forms. He looked to the heavens and saw perfection. A universe that was constant in time. Aristotle also believed in an infinite universe. He thought that the only reason humanity was not more advanced was that natural disasters would put our civilization back again and again.

There is a big problem with that. Hawking writes that if that were the case, it would mean that the stars would have been emitting light forever and making everything around them hotter until everything in the universe is as hot as the stars. The night would be the same as the day because every line of sight that leaves your eye would end at a star or a gas cloud that is just as hot (emitting the same radiation). This implies that the stars could not have existed forever.

Edwin Hubble, in 1929 discovered that almost all the galaxies were moving away from us. If the galaxies were moving away then they must have been very close together in the past. We can trace this back to 13.8 billion years. At this time, everything in the universe was condensed into one infinitesimally small point. That point then expanded into the universe we see today.

Is there other intelligent life in the universe?

There are a lot of necessary conditions for us to exist. We need to be in the goldilocks zone from our star. We need Jupiter to help protect us from comets. We need a moon-earth system. A large number of things must go right, and we are lucky that they do.

If we want to take a step further we can ask why the constants of the universe are what they are? There is no reason for them to be these particular values. For example, solving Maxwell’s equations (of electromagnetism) in a vacuum gives us the speed of light. It is roughly 300,000 kilometers per second. This speed is like a global variable defined (and initialized) in the code of the universe.

Other constants such as the mass, spin of an electron are also fixed quantities. These values form the necessary conditions for complex life like ours to exist. If some of them were even a little bit different, we would not be here. This is known as the Anthropic principle. Roughly speaking, the Anthropic principle says that the constants just have to be what they are to allow us to exist and observe the universe. There could be many universes with different constants. Our universe just happened to have these values to allow carbon-based life to exist.

There is not really an answer to this question until (and if) we get in contact with alien life. I personally find it hard to believe that we are the only life in the universe (statistically speaking). Although, we might be the only intelligent life in our galaxy because there are a lot of things that have to go perfectly for intelligent life to prosper.

Can we predict the future?

In 1814, French scientist Laplace came up with a thought experiment. If an entity (Laplace’s demon) knows the position and velocity of every particle in the universe, it could (at least in principle) calculate the state of the whole universe at any point in the future or the past using the laws of classical mechanics. This is an idea of scientific determinism.

In 1927, Werner Heisenberg showed that it is not possible to simultaneously measure both the position and speed of a particle with complete certainty. This is called Heisenberg's uncertainty principle. One of the most beautiful results of quantum mechanics. The act of measuring the position of a particle changes its velocity in an unpredictable way and vice versa.

Laplace’s demon cannot measure the position and speed of all the particles in the universe with complete certainty, therefore it cannot predict the exact state of the universe at any time in the past or future.

What is inside a black hole?

A black hole is a region in space where gravity is so strong that not even light can escape it. It is formed when a massive star collapses under its own gravity. All that matter is squeezed into an infinitely dense point. This is called a singularity. Einstein’s equations do not work and there is no way to predict what happens at the singularity.

If light cannot escape a black hole, that means nothing can. So, a black hole must get larger and larger as it eats up more and more mass. Although this is mostly true, black holes do “emit” radiation. It is called the Hawking Radiation. This is how Hawking describes this phenomenon in this book.

Outer space is not empty. There are matter and antimatter particles randomly coming into existence. These particles then collide and annihilate each other. There is some energy spent to bring these particles into existence. The universe takes this energy back when these particles annihilate each other, thus preserving the conservation of energy. What if this happens near a black hole. If one of the particles crosses the event horizon (boundary of a black hole) the other is left in space without the partner to annihilate with.

What about the conservation of energy? The universe brought the particles into existence but there was no annihilation. The black hole ends up paying the energy debt to the universe by losing its mass. So it looks like the black hole is emitting radiation.

But that gives rise to another question. The radiation “emitted” by the black hole is just random particles. There is no way of knowing what went inside the event horizon by looking at this radiation. This is called the information paradox. Once something crosses the event horizon, it is forever lost and out of contact with the rest of the universe.

If you want to know more about hawking radiation, the following video is a good place to start :)

PBS space time is one of my favorite channels on youtube. Their name pretty much sums up what kind of videos they make. If you like this stuff, be sure to check them out.