What are the Major Ideas of General Relativity?

When we look at the special theory of relativity, we only consider the effects that speed has on the universe; we neglect gravity. From this theory, we already know that space and time are inextricably linked. Special relativity tells us that there are three dimensions that define space and one dimension that defines time. We call this “spacetime”.

When Einstein extended the theory of relativity to the general case that includes gravity, he discovered that matter shapes the fabric of spacetime in a manner analogous to the way heavy weights distort a taut rubber sheet or trampoline. Of course, it is not as simple as “weights on rubber” because the masses are within spacetime and we cannot directly perceive spacetime. However, using a rubber sheet as an analogy, we can begin to appreciate and visualise the principles of general relativity.

It is difficult to overstate the significance of general relativity to our understanding of the universe. For example, the following ideas all come from Einstein’s general theory of relativity:

= Gravity arises from distortions of spacetime. It is not a mysterious force that acts at a distance. The presence of mass causes the distortions, and the resulting distortions determine how other objects move through spacetime.

= Time runs slowly in gravitational fields. The stronger the gravity, the more slowly time runs.

= Black holes can exist in spacetime, and falling into a black hole means leaving the observable universe.

= The universe has no boundaries and no centre, yet it might still have a finite volume.

= Large masses that undergo rapid changes in motion or structure emit gravitational waves that travel at the speed of light,

~ Troy

Reference: Bennett, Jeffrey. Donahue, Megan. Schneider, Nicholas. Voit, Mark. The Cosmic Perspective, Sixth Edition. San Francisco: Pearson Education, Inc., 2010.

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