Expert: Philip Stahl - 5/12/2006

Question
Hi Philip,

I know that Einstein had done a lot of studies on cosmology. I'd like to learn more about his work, but most websites use a lot of difficult terminologies that a lay person, like I am, find it hard to comprehend. Could you tell me which one of his discoveries in the cosmology area that was really an eye-opening for scientist? What is theory of relativity? What does it have to do with space?

Thank you.

Answer
Hello.

The problem with understanding most of Einstein's work, is that it generally requires an extensive background in mathematics. Even the simpler versions require an ability to use geometry in various novel ways - to see what he is getting at. (As in the case of special relativity).

Re: discoveries, Einstein didn't so much make them, as lay the ground work for them (by others) based on his theory of general relativity.

Basically, there are two theories of importance: the special theory of relativity and the general theory of relativity.

In the special theory, Einstein showed that there is no such thing as an "absolute space or time".  Thus, while to us on Earth such concepts as time, mass, length etc. of an object seem pre-determined and fixed - they aren't for someone traveling at close to the speed of light.

In that case, as Einstein showed, the length of an object contracts, its mass increases, and any clocks it has slow down - the closer one approaches, c ( = 300,000 km/second) the speed of light.

According to Einstein's Principle of Relativity:   "All the laws of physics are the same in all inertial reference frames."

That means, no matter where you travel to in the cosmos - even if it's a planet orbiting a large and massive star, the laws of physics will be the same as here on Earth.

In addition, it implies "the speed of light has the same value everywhere".


Perhaps the primary finding - or "discovery" if you will, of special relativity (apart from the changes in mass, length, time and constancy of the speed of light etc) is that space itself is now a useless concept. It is more accurate to deal with "space-time" (putting the x,y,z dimensions of space together with the t of time to arrive at x,y, z, t to describe ALL events) In addition, from such an integration, one will be led to the fact that:

Energy and matter are the same thing but in different states.

(As conveyed in the equation E = mc^2)

Perhaps the best book to have to learn much more about this theory is:

'The ABC of Relativity' by Bertrand Russell.

You can perhaps check to see if your library has it or do an online search using google to see if it's available at some online venue.

Einstein's general theory of relativity is more to do with cosmology and the large scale structure of the universe. To put it conceptual terms, the general theory of relativity is really a theory of gravity in 4 dimensions (x,y, z and t or 3 of space, one of time). In particular, the force of gravitational attraction arises around large, massive bodies because *space-time* is warped or distorted in their vicinity. A 'well' of gravity is thereby formed, and any smaller or less massive objects move around it. (Much like small ball bearings might move around the inside of a large spinning bowl if you use the right angle)

In practical terms, experiments conducted during the time of total solar eclipse have found that the light from stars sppearing in the (background) is slightly bent or deflected as it passes close by the Sun. This is a direct indication of the warping of the space-time around the Sun.


Also, in the course of a detailed analysis of the field equations of general relativity, the 'Big Bang' actually arose as a solution (when matter is present). The fact that the Big Bang is perfectly consistent with general relativity is a strong argument in its favor. To 9 out of ten cosmologists this was perhaps the most "eye opening" find of all.

Others may well argue that it is more the current finding that the "negative pressure" (which we now believe to underpin dark energy) is consistent with general relativity's allowance for a "repulsive gravity" - since any negative pressure has associated with it gravity that repels rather than attracts. As more evidence comes in that this repulsive gravity is responsible for accelerating the expansion of the universe, it may prove to be the biggest "eye opener" of all!  Especially also if it shows most of the universe is in the form of dark energy and dark matter. (You can 'google' these two terms to learn much more about them)

Unfortunately, there are few 'easy' texts to learn more about general relativity. Even the most basic (assuming they're even available) such as 'Space, Time and Gravitation' by Arthur Eddington, veer into detailed geometry.

Hopefully, this brief overview provided in this reply will prove useful.