Question: I'd like to learn more about Einstein's 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 scientists? What is theory of relativity?
What does it have to do with space?
Thank you.
Answer :
The problem with understanding Einstein's work, is that it
generally requires an extensive background in mathematics. Even the
simpler algebraic approaches (to special relativity) require an ability to apply algebra and intuit geometry in various novel ways - to see what he is getting at.
Re: 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.
As Einstein showed, as an object (mass) approaches the velocity of light (c)the length of an object contracts, its mass increases, and any clocks it has slow down.
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 are in the cosmos 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, based on this, 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 = mc2)
Perhaps the best book to have to learn much more about this theory at a basic level 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. See e.g.
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 appearing 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).
General relativity then, provides the foundational framework for the Big Bang theory. When Einstein's field equations are applied to a uniform expanding universe, they predict space itself has stretched out over time (via the Friedmann equations) back to an extremely hot, dense origin, i.e.
Friedmann showed the field equations cannot produce a static universe, it must either expand or contract. Given we only discern expansion - because of the red shift of galaxies - this means all existing matter must converge into a hot, dense state.
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. Also, by specific Googling you can obtain assorted lectures, say on General Relativity,
General relativity from first principles – Adam Brown
But note these too require some mathematical background (at least through Algebra II), as well as some general physics.
See also:
