Some thoughts on the nature of Space and Time

Michael A Schroeder– March 19, 2018

I’ve been thinking about astrophysics lately. Maybe because it shows up on the science channel a lot. A couple of things kind of stand out for me. One is “Dark Matter” and the other is “Dark Energy.”

These “things” remind me of a past time when people thought the Earth was the center of the Solar System and that the planets orbited in circular orbits. They came up with ways to fit the observed motion of the planets into that model by saying that the planets moved in circles on top of circles.

So what could be wrong with these we-don’t-know-what-they-are things? Where did the idea of Dark Matter come from? Briefly, the existence of an anomaly in the rotation speed of far away galaxies.
The stars near the outside of the galaxies are orbiting the center of mass of the galaxy. The problem is that they are moving too fast, according to current models.

I want to step back and look at the basic assumptions involved with these “facts.”

There are a few permanent assumptions that virtually every physicist believes.

1. The laws of physics are the same everywhere in the universe.

2. The speed of light is a constant.

Well, we know number 2 isn’t true unless you add the phrase “in a vacuum.” One idea is that what is really true is that there is a universal constant (called C ) which is the fastest anything can travel. Light goes that speed when no matter is involved, but it slows down when matter is involved. Why does matter slow down light? Is C changing, or just the speed of light?

Or, maybe SpaceTime is a product of distance and time, so it’s not the speed that changes, but the distance, or time or both. That’s a strange idea, but no stranger than Relativity.

Either way, that SpaceTime is changed by the presence of matter seems evident.

Sound slows down in less dense mediums. I know we can’t equate sound and light directly, but maybe light slows down when SpaceTime is “less dense” because matter takes up some of the space?

Do we know that SpaceTime is the same everywhere? That’s the first assumption. What if it’s wrong?

We say the Universe began something like 13 or 14 billion years ago in The Big Bang. This idea came about from observing the expanding Universe and working it backwards until we arrive at a single point, called a singularity, where the Universe was an unimaginable amount of energy. In a small period of time, that energy expanded, creating the Universe and forming matter. It’s believed that this rapid expansion gave rise to the Universe with all its Galaxies, stars, and planets. It’s also believed that in order for this to all work, the laws of physics must have changed in the first seconds after the Big Bang. Maybe the laws of physics have been changing all along. Maybe the laws of physics are the same everywhere, but not every-when.

Take a galaxy that’s very far away. It takes light a long time to get here. We measure the red shift and calculate its speed away from us assuming that SpaceTime is constant. If C was smaller back in the time when the light left that galaxy, then by the time it arrives here it would have sped up. Wouldn’t we see that as red shift? If the Universe is expanding, and if the amount of matter isn’t changing too much, then we would expect the matter density to be going down, and C would be speeding up.

Perhaps red shift is due to both relative motion and changing SpaceTime. If so, how can we differentiate the two factors in order to understand the Universe?

It’s very hard to understand the shape of the Universe. One popular visualization is the analogy of an expanding spherical surface. If we lived in the two dimensional world of the surface of that sphere we would see all points moving away from us, and our universe expanding. Now that sphere would have been much smaller, in the unseen dimension, and likewise in all surface directions. In the early Universe objects were much closer together. Unless the Universe was expanding faster than C, we would expect light coming from the very beginning to reach us relatively soon, if C was the same then that it is now. In order to still see signals from the early Universe it would have had to circle the sphere, perhaps multiple times. If this analogy is valid, the galaxies we see very far away may actually be older versions of closer galaxies. That could possibly give us a way to measure the size of the Universe, if a way could be found to identify light/radio reaching us for the first and second time from the same source. We would also have to understand what, if any, changes to SpaceTime have occurred during that time. All speculation at this point.

Another thought. According to Relativity, light bends around strong gravity. Wouldn’t we see a very similar effect if the increased concentration of matter near large objects causes a decrease in concentration of SpaceTime? That’s if light slows down near heavy objects, like stars. Wouldn’t it be great if we could recalculate everything and lose the cosmic constant?

This is what I’ve been pondering recently.

Michael A Schroeder