As those who have seen Jurassic Park will know, this means a tiny disturbance in one place, can cause a major change in another. A butterfly flapping its wings can cause rain in Central Park, New York. The trouble is, it is not repeatable. The next time the butterfly flaps its wings, a host of other things will be different, which will also influence the weather. That is why weather forecasts are so unreliable.

It is impossible to imagine a four-dimensional space. I personally find it hard enough to visualize a three-dimensional space!

We should seek the greatest value of our action.

It's the gravity that shapes the large scale structure of the universe, even though it is the weakest of four categories of forces

Once I wept for I had no shoes. Then I met a man with no feet, so I took his shoes. I mean, it wasn't as if he was going to need them.

There are no black holes - in the sense of regimes from which light can't escape to infinity. There are however apparent horizons which persist for a period of time.

One might think this means that imaginary numbers are just a mathematical game having nothing to do with the real world. From the viewpoint of positivist philosophy, however, one cannot determine what is real. All one can do is find which mathematical models describe the universe we live in. It turns out that a mathematical model involving imaginary time predicts not only effects we have already observed but also effects we have not been able to measure yet nevertheless believe in for other reasons. So what is real and what is imaginary? Is the distinction just in our minds?