Theories of the Universe: Recapping Relativity

Recapping Relativity

We've now covered the relative nature of five things: motion, time, space, energy, and mass. Let's just summarize what we know about this before moving on to Einstein's theory of general relativity. To begin with, everything looks different from different points of view. If some people are moving past you close to the speed of light, they seem to get very massive. They however, will not feel themselves getting more massive. They will see you getting massive.


It's interesting to extend Einstein's idea of a “proper” view to other areas. From a cultural perspective it's often the case that whatever we do is proper and normal and whatever “they” do appears peculiar and weird. Have you ever met a parent who thought anyone but himself or herself knew the “proper” way of raising children? Even national populations consider their political ideas as normal and proper, while other nations aren't quite at the same level. You can tie this all into our previous discussion of truth from “Evolution vs. Creationism.”

Objects, people, planets, and stars—anything that moves very fast in relation to you—appear to get more massive. The increase in mass is based on motion: the greater the speed, the greater the increase in mass. But motion, as Galileo observed, is relative. A clear perspective about who is moving and who is not depends on your frame of reference, your point of view. So a judgment about how massive something is must also depend on your point of view. And what holds for mass must also hold for energy. If the energy of motion at high speeds can be converted into matter and vice versa, then it's clear that how much energy you have depends on how much motion there is. So energy in this sense is relative, too.

​ The Einstein Turm astrophysical observatory ​
Einstein Turm astrophysical observatory in Potsdam, Germany

This same understanding also applies to time and space. Travel at speeds nearing the speed of light cause your clock ticks to tick more slowly and your space to contract. But these effects are necessarily relative to something else. For example, if a friend of yours stays home while you whiz off on a quick trip around the galaxy, you may return to earth still relatively young (of course, that all depends on how old you are when you leave) years after your friend has died of old age. But you stay young only relative to your friend and the rest of your family at home. According to your internal biological clock, or wristwatch, or any other timekeeping apparatus, time flows as always. You can't tell that time has slowed down for you, because your entire frame of reference is running slower; your heart rate has slowed down, your breathing slower, all bodily functions are operating at a reduced pace. Even atomic clocks would run slower.

Universal Constants

One of the main goals of physics is to bring together all of the forces, energies, particles, and theories into a unified system. This is the Holy Grail that physicists are searching for. It's also known by various other names such as the Unified Field Theory, the Theory of Everything (TOE), or a Grand Unified Theory (GUT). Einstein tried to accomplish this but never succeeded. It's been partially completed, but the final unification of the microcosm with the macrocosm—quantum mechanics and general relativity—is still on the drawing board. The best theory to date is the string theory, which we'll be getting to in “The Accelerating Universe.”

The result of all this is that you have no way of knowing whether you are more massive or not, whether your time has slowed or not, whether your space has contracted or not, or even if you are moving or not, just like the person on Galileo's ship. Your mass is normal mass, your time is normal time, and your space is normal space. Everything in your view seems appropriate and proper, while things and people moving relative to you appear slow moving, squashed, and weird. Einstein called the view which you see the “proper” view, to distinguish it from other frames of reference.

The bottom line to all of this is that things look different from different points of view. The simple observation of a cardboard box can look different depending on whether you're speeding past it in a car or standing next to it. The box itself doesn't change, and the laws of nature don't change. The relationships between objects and events don't change. That's why you can't tell whether or not you're moving, or if your clock is running slow. From within the confines of our own limited perspective, things seem very different where in truth they are very much the same. The equations of relativity can provide a kind of dictionary that helps to translate from one frame of reference into another. They allow you to move step by step to someone else's point of view. Relativity can essentially mean that everybody can agree on the facts of a situation, even though we all see it from vastly different points of view. So motion, time, space, energy, and matter, we could say, form the core cosmological structure of the universe within the framework of the scientific paradigm. And our understanding of these five, in essence, really seems to depend on our point of view.

Relativity theory also shows that the perspective of a constantly changing, dynamic cosmos has the potential to be understood from a unified system. And although the ideas contained within relativity theory have united these five things through changing perceptions, it's not quite that simple. There are other forces and structural problems that need to be addressed. We've only dug three feet out of a ten-foot hole. But unification is the ultimate goal. That will become a major focus. The next thing we have to examine is the universal force of gravity.

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Excerpted from The Complete Idiot's Guide to Theories of the Universe © 2001 by Gary F. Moring. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.