Expansion of the Universe
Earth and Space

The Universe

Physics Narrative for 11-14 Supporting Physics Teaching

Some ideas about the universe

The universe is the sum total of everything that exists – the aggregate of existing matter, radiation, time and space. The most easily observable element is the matter that exists as stars, most of which is collected in galaxies. There are millions and millions of galaxies in the universe.

James Jeans once said, in answer to the question: How many stars are there?

There are as many stars in the universe as there are grains of sand on all the beaches in the world.

Currently, it's estimated that there are 100 000 000 000 galaxies in the universe. They are not evenly distributed, but appear in clusters. However, as well as matter, there is a large amount of energy and invisible matter. Some of this is in black holes, which do not emit light and cannot be seen.

The age of the universe is calculated from the discovery made by Edwin Hubble that the universe is expanding. Hubble observed that the light from all stars appears to be shifted towards the red end of the spectrum. An analogous effect is the drop in the note of a police siren as it passes you and moves away.

As the universe is expanding, the frequency of light becomes lower, that is light becomes more red. From the change in frequency, you can infer how fast the object is moving away.

By plotting a graph of the velocity of recession of stars against distance, it is possible to work backwards to find how long ago the process must have started. The current answer is about 13 billion years.

Is there likely to be life elsewhere in the universe? There is a good chance that there is, although there's no certainty.

When a star is created there is thought to be about a 1 in 3 chance that it will form with an orbiting planet or planets – that's a prediction from computer modelling. However, through improved technology, astronomers are now beginning to detect the presence of planets around other stars and these findings support the models. What is known is that in our own solar system 1 in 9 of the planets has life on it. Assuming this is typical, in itself a major assumption, you might think that there are an awful lot of stars with planets that might have life on them.

The next big question is how long is it before intelligent life appears? In our own case this was roughly 3000 million years. And, when it does appear how long is it likely to last? Even if intelligent life lasts for only 100 000 years, the calculations suggest that there should be many other planets out there with intelligent life.

Since the late 1960s astronomers have been searching for radio signals that have a non-random pattern. Signals of this nature might be emitted by civilisations that have evolved to a sufficient level to produce the technology to transmit radio waves. None has been found so far, but this does not necessarily mean that we are alone. There are a host of other explanations, with the most obvious one being that our instruments are not sensitive enough to detect the signals.

In the words of Carl Sagan, an American astronomer:

If we are alone in the universe, then it is an awful waste of space.

Expansion of the Universe
is formalised by Hubble's Law
is described by Dark Matter Dark Energy
can be analysed using the quantity Hubble's Constant
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