By Roland Watson

So far in this series, I have been exploring deeper and deeper aspects of universal order. But, with one or two exceptions, all of this has been from the first perspective on the universe, which is via its separate parts and their interactions.

I've also mentioned that there is an alternative, which is to view the universe as a whole, meaning, in practical terms, to make a distinction between matter-energy and the space-time that it occupies. This in turn brings us to the second major theory of modern physics: general relativity - although I have already mentioned it a bit in the discussion of symmetry.

The view of the parts - quantum mechanics - seeks to explain reality at the level of the very small: what happens to subatomic particles, and what they are. Relativity theory, on the other hand, is for the most part applied to the very large: to stars, galaxies, and the entire universe. Both theories also work, in the sense that they consistently make accurate predictions of reality - or at least of our experiments on it; but both also suffer from some specific failings, are replete with unknowns, and are not completely consistent with each other. For example, there is no chance element in relativity.

Another way to phrase general relativity's symmetry of equivalence is to say that, depending on your state of motion, a system will appear to be in an inertial state; subject to a gravitational field; or experiencing acceleration. In other words, there really is no way to tell if you are moving or not. Your view is dependent on, and biased by, your specific frame of reference. Also, this means it is still open to debate if we actually are subject to, or even if there is such a thing as, gravity.

The significance of space-time

Relativity theory has had a profound consequence on our conception of space and time. Indeed, while we view space and time as different and distinct, since to us they have different characteristics - we can move about in space, but - seemingly - not in time, we now understand that they are inseparable. Also, space-time is considered to be continuous, as opposed to the discontinuous aspect of matter-energy. It can, in theory at least, forever be broken into smaller and smaller pieces.

We can see space, as by looking across a room, and we can even see time, as with the movement of something, or even when there is no movement, simply through continuing to see. However, we do not actually perceive space and time as being together. But, Einstein proved that they are together, and furthermore that they are "curved."

Under relativity theory, there is no such thing as gravity, at least in the sense of a force. Quoting David Peat again,"What looks like the force of gravity is really the curvature of space-time."

As with particle/wave duality, this is another one of the ideas from theoretical physics that is difficult to envision. For instance, space-time can be viewed as a flat two-dimensional field with three-dimensional distortions - curves - where matter-energy is present. Anything moving through space-time has to go around these distortions or curves. Hence, planets in orbit around the sun, and light bypassing it, are not being pulled to it by its gravity; they merely are traversing a massive distortion in space-time, by following the shortest curve around it. In effect, they are following the path of least resistance. Said another way, the sun curves space, and the planets, and light coming towards us from distant stars, follow this curve. The curvature of space-time by matter-energy produces gravity.

One final way to imagine this, the curvature of space-time around matter-energy, is to think of all the separate aggregations of matter-energy in the universe as a collection of floating holes, all of which reach out in all directions across the entire universe, and all of which are falling into each other. Can you picture this?

I can also note that the principle of least action in quantum mechanics is similar to the process by which matter-energy follows the path of least resistance through curved space - the space that has been curved by other accumulations of matter-energy. The first applies to sub-atomic particles; the second to their aggregations.

What is gravity?

Many physicists, including Stephen Hawking, are trying to unify quantum mechanics and relativity theory by creating a quantum theory of gravity. They are looking for a virtual particle called a "graviton," which would be exchanged over the long distances between the protons, neutrons and electrons in the atoms of neighboring celestial bodies.

Another group, the string theorists, view everything - all matter-energy and space-time - as a network of extremely small strings. Particles are strings. And, the forces between particles, including gravity, also are strings, pulling the strings that constitute the particles together. The universe is comprised of strings interacting with strings.

More precisely, all of the different types of particles, both matter and force, represent identical underlying strings, but with different vibrational patterns, which patterns themselves determine how the strings interact. Gravity represents, according to Brian Greene, "an enormous, organized array of similarly vibrating strings." Such an array is also known as a "coherent state."

Relativity theory is further the source of the view that particles are "a series of events." From Bertrand Russell: "Each event had to each other a relation called 'interval' which could be analyzed in various ways into a time-element and a space-element." Also, "'matter' is not part of the ultimate material of the world, but merely a convenient way of collecting events into bundles."

I want to emphasize the point that Russell makes here. He is arguing that matter itself is not fundamental. Rather, space and time are.

As an aside, this idea also has an implication for my introductory discussion on the concept of form: that at its most basic level it is any thing or process. Under relativity theory, "things" and "processes" are combined into "events." Therefore, a form and an event also are equivalent.

What is invariant?

There are many other interesting outcomes of relativity theory, including that there is no absolute non-motion. This also implies that there can be no void, no empty space, in space-time, because in effect it would be at rest. Indeed, this is further evidence that subatomic particles cannot be particles, because of the empty space that would exist between them, such as between the particles in the atomic nucleus and also between the nucleus and its electrons.

The curiosities that derive from relativity theory are all the more noticeable when we get to time. Under relativity, matter is proportional to energy and space is inseparable from time, and time - and hence space - is relative to the motion of matter - and hence energy.

Relativity has a very famous consequence. The perspective of time varies according to the motion of the observer. People, or for that matter objects, moving at different velocities, experience time at different rates. This in turn implies that two events that seem simultaneous to one person, may be sequential to another.

Furthermore, these observers will actually age at different rates. The faster you move, the slower you age. Of course, such effects are only noticeable when the motion is very fast - or the rate of relative motion between the observers is very great, at velocities close to the speed of light. Nonetheless, they exist at every level. You age at a slower rate when you are on a plane. However, time also accelerates the farther you are from massive space-time distortions, such as the earth, so when you are flying, high above the ground, the reduction in the rate of time passing is partially offset by this.

What all of this means is that there is no universal time: no standard clock ticking though the ages. Time is not a constant. It varies everywhere. But, the basic point of relativity is to determine not what is relative, but what is invariant, meaning, as Hawking put it: "the laws of science should be the same for all observers." Einstein actually wanted to call his theory "Invariance Theory." Also, the theory shows that the space-time interval between two events, the combination of their distance in space and change in time, is invariant, regardless of the motion of any observers to, or participants in, such events.

Another thing that is invariant is the speed of light. Regardless of your state of motion, it never changes. The reason for this is that your "clock" changes. It slows down as you speed up, and vice-versa, with the net effect that the speed of light remains the same.

Also, and as I have said, the speed of light is a limit. It cannot be exceeded. As matter is accelerated, it takes on the energy of its motion, but since energy is proportionally equivalent to matter, the effect is to increase its mass. You may age slower on a plane, but you weigh more!

But, at the speed of light the increase is so great that mass becomes infinite. To move the matter just a little bit faster, so that it exceeds the speed of light, therefore requires infinite energy. Light itself travels at its speed because it - photons - have no mass.

Mass is the amount of energy that it takes to counter inertia, to move an object at rest. Of course, nothing is ever at rest. An object sitting on a table has the relative motion of the earth. One could then argue that it takes no energy to move light, that it is not "an object" - although it does have a "material" effect - it warms us!, and that it, along with virtual particles, are cases of something that actually are nothing. Indeed, a related view is that this is allowed because it transpires in no time. At the speed of light, time stops, which begs the question, how can we see it - light - and therefore how can it both occupy, and be beyond, time?

Velocity is invariant

Finally, a fascinating extension of the fact that space-time intervals are invariant is that everything travels at the speed of light, all the time. It is just that part of the velocity is through the space portion of space-time and the balance through the time portion. Quoting Greene again, "Not only can spatial dimensions share an object's motion, but the time domain can share this motion as well. … in the majority of circumstances, 'most' of an object's motion is through time, not space." Light in fact never gets old, because all of its motion is through space. But we, you and I, are moving at the speed of light, too. Our velocity through space, of which the vast majority is accounted by the earth's rate of orbit around the sun, is a small fraction of our velocity through time. Not only are our lifetimes short. We rocket through them at close to the speed of light!

In summary, these are the types of conceptual difficulties that derive from relativity theory. But, it also has a problem, or rather it is incomplete, from another perspective as well. As quantum mechanics cannot predict the actual behavior of specific particles, relativity theory cannot tell us what happens inside singularities: in black holes, or during the Big Bang. In such situations space-time is "destroyed," and the normal laws and principles of physics do not work. More fundamentally, there is no explanation from relativity theory of why space-time distortions exist, what the distortions really are, and what space-time itself is: what it is made of.

In the next article, I will consider the possibility that the universe is comprised of either matter-energy or space-time, not both - that only one is elemental.

© Roland Watson 2015