DARK MATTTER
by
ROY PACKARD
I drove down to Seal Beach today. Got a cup of coffee at Bogart's and walked across the street to Eisenhower Park - a piddling little park of about a quarter of an acre in size - but nice. Got a bench overlooking the ocean and sat and did what old men do - supped my coffee, watched the pretty girls and dreamed of days gone by. There weren't any girls today. Just one old lady in a wheel chair being push by her husband who was also in a wheel chair. So I sat and dreamed of days gone by.
Beautiful day. Could not have been more so. The temperature was 71 degrees F. There was a gentle Santana wind wafting down from the mountains and out to sea. The water was calm. Three surfers hoping for some waves but not getting any.
All was quite.
So I sat and supped my coffee.
And thought again about this dark matter problem.
Theorists have been concerned, for some time now, because they can account for only 13% of the total mass of the Universe. That 13% includes everything we know - you, me, little babies, the Earth, the Sun, the Solar System, all the galaxies and all the stars and planets in the Universe. They know the other 87% is out there; they just don’t know where.
Before I proceed, a little refresher course in scientific notation may be in order. Very large numbers and very small number can take up a lot of space if written in the normal manner using decimal places as you were taught in high school.
For example, the number of atoms in the Universe is 10 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 plus or minus a few. Well, you don’t want to be trying to say that nor writing that down every time the subject comes up, so a short-hand scheme is available using exponents. The same number can be shown as 1e79. Isn’t that a lot easier? (Perhaps Obama ought to start using scientific notation. His 16,000,000,000,000 debt could be expressed as 16e12. Isn’t that so much more pleasing?)
Now, we get to the heart of the matter.
Since the Big Bang, light has been emitted into the Universe. Every visible object we see is emitting or reflecting light. Let us concentrate our attention on stars since those generate the most light. Planets, meteorites and asteroids give off reflected light. Standing here on Earth we see stars as a small dots or spheres. But those stars are emitting light out in all directions creating a light sphere. Standing anywhere else in the Universe we would see the same stars as small dots or spheres.
The fact is, we cannot see light. We can see the source of light and we can see the objects from which light is reflected. Otherwise, when we look out into the Universe, we would see nothing but light. (Try this. Don a space suit, grab a flashlight and step outside the ISS (International Space Station). Now, aim the flashlight away from you and turn it on. You see nothing. Put your hand in front of the flashlight and you see your hand. Aim the flashlight toward you and you see the source.)
All those stars pumping light out into space. Some since the beginning of time, as we know it. And that light is still out there. We just don’t see it.
And what if that light had mass?
In fact, it does. Not a lot, but it does.
The rest mass of a single photon of light at a wavelength of 500nm is 4.417e-36 kg. That's 4.417 with 35 0s to the left of the 4 - a very small number.
The volume of the Universe is 2.058e79 cubic meters. That's 2.058 with 76 0s to the right of the 8 - a very large number.
So, how many photons would be required per cubic meter of the Universe if all the dark matter is really light?
The mass density of the Universe is 6.000e-27 kg per cubic meter. By dividing the mass density of the Universe by the mass of a photon, we get 1.358e9 photons per cubic meter - a very plausible number when you figure the mass density of photons near the Earth is 4.217e13 photons per cubic meter.
So, I am going to go with that. Dark matter is really light. Now all I need to do is to convince a bunch of very bull headed and exclusive theorists of it. They don't like outsiders messing around in their area.
