**Ask a monkey a physics question thread**

[CoccoBill]

More geometry than physics I guess, but if you were looking up at space from earth and had vision good enough to see to the edge of the observable universe, what percentage of your field of view would be covered by matter (stars, planets, comets, what have you)?

[MadMojoMonkey]

More geometry than physics I guess, but

Well, it's about what is/can be observed... which sounds a lot like physics.
If not physics, then chemistry or biology.

and had vision good enough to see to the edge of the observable universe

It's hard to imagine what kind of vision I have if it can't be used to observe the universe. I'm assuming you're talking about visible light, yeah? If a telescope can absorb a photon and that is an observation, then if my eye was where the telescope is, my eye would have absorbed the photon and observed it.

The advantage of a telescope is that it is like a very big eye. I mean... it gathers photons from a much bigger area than a pupil. Also, the camera or CCD doing the actual "observing" has the benefit of using long exposures for a single frame. Whereas my brain keeps telling my eyes to forget the past and focus on the present.

I'm saying that you CAN see to the edge of the observable universe, although the stuff that's very far away is also quite dim. So much so that it doesn't register as more than black to our fast-paced, tiny eyes. Still, it has been shown that at least some people's eyes are sensitive enough to detect a single photon, so even though you may not consciously observe it, that photon has traveled from the edge of the observable universe to your eye.

if you were looking up at space from earth, what percentage of your field of view would be covered by matter (stars, planets, comets, what have you)?

OK, so I need to do a bit of digging for this to be more than a hand-waving guess.

I will answer this question soon.

First tactic will be to examine the Hubble Deep Field Survey and see what percentage of that shot was filled with visible stuff (galaxies).

EDIT: It's harder than I thought. My rough estimate is ~30% ish... but you could guess the same thing if you look at any of the various deep field surveys. I do suggest it. Here's one:

Kind of in the middle of the lower-right quarter of the main image, there is an 8-pointed star. That is a star in the Milky Way. I don't see any other 8-pointers, but they would also be foreground objects. The 8 points are diffraction caused by the optics in the HST. Everything else is a galaxy.