Reflections on Cosmology

Big Bang

I have a question about your article "Why is the sky dark at night?" I do have a basic understanding of physics, although having never heard of this theory before maybe I don't. Don't ... know about the theory, or have an understanding of physics? Not clear. I understand everything that you have written in your article, I have even done some side research on dark matter to further add to my knowledge. I think my problem might be that my base assumption of the universe is wrong.

I had always pictured the universe as an explosion inside of an infinite vacuum. But that would divide the universe into a hotter center and a colder periphery, a division for which there's no evidence. Good evidence points to a singularity at the beginning of the universe that represented all time and space collapsed to a point, followed by a uniform expansion with no center and no periphery. It's not an expansion into a pre-existing space, it's an expansion of space itself. Modern, very sensitive measurements support this idea by not finding any preferred directions in space. The explosion of course being the Big Bang and this is expanding at a phenomenal rate through this vacuum. That's inconsistent with the idea of an initial spacetime singularity, a collapse of both space and time that doesn't allow for either an "outside" or a "before".

A good argument against the idea of a free lunch, where all the mass-energy of the universe arose out of nothing (an idea that would violate energy conservation), is the idea that positive mass-energy, represented by stars, planets and photons, is exactly balanced by the negative energy of gravitation. This balance means the universe could pop out of nothing without breaking any physical rules, by way of a random quantum fluctuation. It's just as though the entire universe was a transient virtual particle.

An argument for uniformity in the structure of space-time (with no "outside") is that it's a simpler explanation than the alternative of a hot bubble sitting in the middle of an infinite expanse of vacuum. An argument against the isolated bubble idea is that either (a) we happen accidentally to be in the precise middle of the expanding bubble, or if this isn't true then (b) we would be able to detect a variation in the background radiation / population of galaxies in a particular direction (the direction of the primordial vacuum, and opposite the "center", the location of the original big bang).

But we don't see any such variation — the background is remarkably uniform. It's important to reëmphasize that the absence of a background asymmetry strongly argues against the idea of a hot central universe expanding out into a vacuum. Although I do see that the expansion of this dark matter around clusters of galaxies ... No, wait — that expansion is thought to result from dark energy, not dark matter. Dark matter is what supposedly holds galaxies together in ways not explainable by visible matter. Consider these observations:

Observation: galaxies are rotating faster than their visible matter can reasonably explain — they should be flying apart. Explanation: there is some unseen kind of matter (dark matter) that holds galaxies together against their own rotation.

Observation: The universe's overall expansion is accelerating — technically, the second derivative of position (acceleration), which should be negative (arising from gravitation), is instead positive at great distances. Explanation: dark energy, a universal repulsive force that works differently than gravitation (having no inverse square law, for one thing).

This may help clarify things:

p(t) = position, a function that provides locations of stars and galaxies with respect to time.
p'(t) = first derivative of position, or velocity.
p''(t) = second derivative of position, or acceleration.

In this simple Calculus scheme, velocity (p'(t)) is the time integral of acceleration (p''(t)), and position (p(t)) is the time integral of velocity (p'(t)). This scheme is called a "differential equation", something at the heart of mathematical physics.

The quantities are related like this:

              p''(t)  —>  p'(t)  —>  p(t)
              Acceleration  Velocity   Position

In this scheme, gravitation and dark energy (with opposite signs) give rise to acceleration, acceleration changes velocity, and velocity changes position. All these values are signed numbers — they can be positive or negative. A ball accelerates while being thrown (positive sign), to later decelerate as a result of gravitation (negative sign). ... will have a cooling effect on the universe ... Not if matter is being pushed out against gravitation by an energy source. This would prevent any overall cooling. The cooling one would expect to see from the expansion is to some degree countered by the energy contributed by the expansion force (dark energy).

When water becomes steam, this represents an expansion, but the water doesn't become cooler in the process. The heat source responsible for the water —> steam transition provides the required energy. In the same way, as dark energy overwhelms gravitation, it also moderates the cooling effect of expansion. Put another way, the expansion isn't ballistic but is driven by an energy source. I also keep coming back to a heat source trying to warm up an infinite vacuum, which would be impossible. Hence the sky is dark. Can you please point out my error. There isn't any evidence for an infinite vacuum, and very good evidence against this idea. Again, if the universe were a finite ball of matter expanding out into an infinite vacuum, we would be able to sense the direction of the center of the mass (hotter) and its polar opposite, the direction of the infinite vacuum (cooler). But in exquisitely sensitive measurements, we don't see that. This can be explained away by the idea that we happen to be at the exact center of the ball of expanding matter, but this argument isn't persuasive. If you could please supply me with some feedback to my problem, if you have some time, it would be much appreciated. Why [sic] you are at it can you also think of a rational explanation as to why this is not taught at school, something so relevant to every person who has ever looked up at the stars, everybody, should be mandatory teaching. It's taught in school — but only to the degree that religious fundamentalists allow it to be taught. That means it is taught in detail at the college level, but not so well at lower levels.

To religious fundamentalists, any evidence for a world/universe older than about 6,000 years is blasphemy, so any substantial treatment of cosmology is either removed from public school textbooks or glossed over with little substance. Also thanks heaps for your site. I found it by accident after being forced to endure the MBTI (Myers-Briggs Type Indicator) test. I have never felt so frustrated in my life and I hit Google when I got home and found your article on why psychology is not a science, I found it helped me understand my frustration and why I could not grasp any relevance from the whole test. If your curious I got graded as an INTP, I always thought I was a Leo. Very funny! Logician Raymond Smullyan says he doesn't believe in astrology, but only because Geminis don't believe in astrology.

Thanks for writing.