Did You Know: Space – Where did the universe come from? Everything that exists all began to form around 13.8 billion years ago, during an event called the big bang. The big bang started the creation of the universe and everything in it, including us! How do we know how old the universe is? Universe … Read more
Where does space begin? Space begins at the Karman Line, which is 62 miles (100 km) above the Earth. This is the height you need to reach to become an astronaut. Humans can’t survive in space, but are protected by layers of gas that surround the Earth. These layers are called the atmosphere. What is … Read more
Did You Know: Space – What is space? On cloudless nights when you look up at the dark sky, you can see space. It stretches much farther than the eye can see and contains the moon, the sun, all the planets, as well as the Earth, and the stars. Space also contains many things that … Read more
A Briefer History of Time – Stephen Hawking Another problem is that there are at least four different string theories (open strings and three different closed string theories) and millions of ways in which the extra dimensions predicted by string theory could be curled up. Why should just one string theory and one kind of … Read more
A Briefer History of Time – Stephen Hawking String theory has a curious history. It was originally invented in the late 1960s in an attempt to find a theory to describe the strong force. The idea was that particles like the proton and the neutron could be regarded as waves on a string. The strong … Read more
A Briefer History of Time – Stephen Hawking As was explained in the first chapter, it would be very difficult to construct a complete unified theory of everything in the universe all at one go. So instead we have made progress by finding partial theories that describe a limited range of happenings and by neglecting … Read more
A Briefer History of Time – Stephen Hawking The last chapter discussed why we see time go forward: why disorder increases and why we remember the past but not the future. Time was treated as if it were a straight railway line on which one could only go one way or the other. But what … Read more
A Briefer History of Time – Stephen Hawking The quantum laws are more liberal and allow you to be overdrawn on one or two accounts provided the total balance is positive. In other words, quantum theory allows the energy density to be negative in some places, provided that this is made up for by positive … Read more
A Briefer History of Time – Stephen Hawking But why should the thermodynamic arrow of time exist at all? Or, in other words, why should the universe be in a state of high order at one end of time, the end that we call the past? Why is it not in a state of complete … Read more
A Briefer History of Time – Stephen Hawking In previous chapters we have seen how our views of the nature of time have changed over the years. Up to the beginning of this century people believed in an absolute time. That is, each event could be labeled by a number called “time” in a unique … Read more
