You might think physicists have “solved” the problem of space. The likes of mathematician Herman Malinowski and physicist Albert Einstein taught us to conceive space and time as a unified continuum, helping us to understand how very large and very little things such as individual atoms move. Nonetheless, we haven’t solved the question of what space is. If you sucked all the matter out of the universe, would space be left behind?

You might think physicists have “solved” the problem of space. The likes of mathematician Herman Malinowski and physicist Albert Einstein taught us to conceive space and time as a unified continuum, helping us to understand how very large and very little things such as individual atoms move. Nonetheless, we haven’t solved the question of what space is. If you sucked all the matter out of the universe, would space be left behind?

Space is also filled with many forms of radiation that are dangerous to astronauts. Much of this infrared and ultraviolet radiation comes from the Sun. High energy X-rays, gamma rays and cosmic rays – particles travelling close to the speed of light – arrive from distant star systems.

Caroline was a keen philosopher, and in the early 18th century she schemed to pit the leading philosophies of her period against each other. On the continent, philosophers were stuck in “rationalism”, spinning world theories from armchairs. Meanwhile, British philosophers were developing science-inspired “empiricism” – theories built on observations. They were worshiping scientists such as Robert Boyle and Isaac Newton.

Space is usually regarded as being completely empty. But this is not true. The vast gaps between the stars and planets are filled with huge amounts of thinly spread gas and dust. Even the emptiest parts of space contain at least a few hundred atoms or molecules per cubic meter.

Outer space' begins about 100 km above the Earth, where the shell of air around our planet disappears. With no air to scatter sunlight and produce a blue sky, space appears as a black blanket dotted with stars.

Is space is infinite?

Two possibilities exist: either the Universe is finite and has a size, or it's infinite and goes on forever. Both possibilities have mind-bending implications. In another episode of Guide to Space, we talked: "how big is our Universe". Then I said it all depends on whether the Universe is finite or infinite.

We can use extremely accurate atomic clocks to measure exactly how much the rotation is slowing down. One hundred years from now, a day will be about 2 milliseconds longer than today. Two milliseconds is 1/500th of a second, or how long it takes a car going 55 mph to travel only 2 inches--in other words, much less than the blink of an eye.