what are the limits of space

For many years children have taken comfort in the belief that even Albert Einstein (1879-1955) was a failure at school. But the school records of the German-born physicist who devised the theory of relativity show that in fact Einstein was exceptionally gifted. He excelled particularly in physics, mathematics and music.

The misunderstanding may have arisen because during Einstein's last year at school in Aargau, Switzerland, in 1896, the school's system of marking was reversed. Grade 6, which had been the lowest mark, became the highest and Grade 1, which had been the highest, became the lowest. To anyone who did not know of the change, it could have appeared that Einstein's marks had plummeted.

Einstein did fail entrance exams for the Federal Technical Institute in Zurich, but this may have been because of his one area of great weakness: French. It may also have been because he took the exams at the age of 16 - two years younger than normal. Instead Einstein was sent to Aargau and went on to the Zurich institute two years later.

The farthest object clearly visible to the naked eye is a spiral galaxy named M31 in the constellation of Andromeda. On a clear night. it appears as a small hazy patch. The Andromeda galaxy is 2.2 million light years away, which means that the light we now see from it began its journey when man's ape-like ancestors were still roaming the plains of Africa.

Carbon atoms often link with others in such a way that two molecules can have the same number of atoms and the same structure-and yet be different because the twins are mirror-images of each other. Like a pair of gloves, the twins are not interchangeable, and in living organisms only one of them is likely to be useful.

Amino acids, the building blocks for proteins, mostly occur as one type of these pairs, while their mirror-image molecules are not capable of being used to make protein. No convincing explanation (other than pure chance) has been found of why life on Earth has developed on one side of this twin relationship and not the other.

Scientists have speculated that life elsewhere might be based on similar molecules but with the opposite sets to those on Earth. A visitor from such a planet would starve to death on Earth because he would be unable to digest the proteins in earthly food.

Most modern astronomers believe that man may already be able to see nearly as much of the Universe as will ever be possible. The belief rests on a discovery made by the American astronomer Edwin Hubble. In 1929. he found that the more distant a galaxy was from our own, the faster it was moving away.

Hubble made his discovery by analysing the light from distant galaxies. In 1912 a US astronomer, Vesto Slipher (1875-1969), had discovered that this light was shifted towards the red end of the spectrum. Hubble worked out why-that it happened for the same reason that the pitch of a police siren drops as the police car moves away from the hearer.

The galaxies were moving away from the Earth. The farther galaxies had more pronounced red shifts than nearer galaxies, and the amount of the shift gave a clue to the speed of the galaxy. The relationship between this speed and the galaxy's distance is known as Hubble's Constant. In its modern form, the constant suggests that for every 1000 million light years between any two galaxies, their relative speed of separation is slightly less than 10 per cent of the speed of light.

If Hubble's Constant holds good to the most extreme distances, there will finally come a point where galaxies are receding from us at the full speed of light. As a result. their light along with any other radiation they emit will never reach us and no human observer will ever be able to detect them. This critical distance for the boundary of the observable Universe-though not necessarily the boundary of the Universe itself-is believed to be about 15,000 million light years from Earth.

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