If we can measure energy in space, what about stray matter?

Question

How is it measured?

Is it by particle density, or is by the cubic meter?

Answer 1

Density,

We can only observe matter in space like asteroids, planets, and stars. There are two ways to determine what it is made of. First when a substance is burned it gives off colors on the spectrum, and each element has its own combination of colors. Once you allow for the red shift from distance you can identify what is being burned. We know that you can't have anything lighter than hydrogen and the most stars are burning hydrogen. Based on that you can calculate the distance and the red shift to figure out what else is burning in that sun.

The spectrum continues beyond the range of visible light so if you burn an element in x-ray radiation then you can locate the element on the spectrum by what wave lengths of radiation are visible.

In space we determine what most matter is by seeing it burnt by a star or some sort of radiation. This is how we know that you can find simple chemicals like formaldehyde in some stellar nebulas.

If you know what the elements or the compounds are then you can determine the weight of it. A pound of hydrogen under 1 G has the same weight, under 1 G, anywhere in the universe. So once we know what an item is we can find its weight. The other factor is how thick, or how dense the matter is. We detect a lot of items by observing what happens to the radiation of the star when something passes between it and us. The amount that this radiation is dimmed will tell you the density.

If you look at hot dust near a star you can tell what elements are in it by the spectrum, the amount of light blocked by the dust will tell you how dense it is and that can tell you how much it weighs. This is real helpful when studying comets since they have a burning tail. Asteroids are mostly iron and nickel and we have found a lot of other heavy metals in them (by looking at the ones we found on the earth) so we can make assumptions about what they are made up of, but these are educated guesses. We are more sure what is in a comet because we can analyze the tail.

Answer 2

The estimated density of the observable universe is 2.11^ minus 29 (..2.11 preceded by 29 zeros..) kilograms per cubic meter. This density is molecular.