# Can the human eye see the edge of the Universe?

After viewing the stunning new photographs returned by the Hubble Space Telescope, I got to thinking. I realize that standing in my back yard, I couldn’t see the edges of the universe with as much resolution as Hubble, but could I see as far?

You can see the Andromeda galaxy with the naked eye from your back yard. At 2,900,000 light years distance, it’s the nearest large galaxy. Everything further is too dim for a merely human eyeball to pick up.
The Bad Astronomer on How Far can you See?

You cannot see the edge of the Universe, because there is no edge to the universe. If there were an edge, what would be past the edge? The Universe is, by definition, all that there is.

No, and interestingly, I think it is a resolution issue. There is too much “stuff” in our atmosphere (dust, etc.) to allow you to see any but the largest and brightest objects in space.

WAG quotient of this answer: 28.4%

No…you can’t see that far. Nothing can. Light travelling from the ‘edge’ (there isn’t a literal edge per se) of the Universe hasn’t reached us yet. The farthest you could theoretically see is the distance light can travel since the beginning of the Universe. If we assume that the Universe is 15 billion years old then the farthest you could potentially see is 15 billion light years.

The farthest object that can be seen with the unaided human eye is the Andromeda Galaxy (M31) at around 2 million llight years away from us (it’s the closest galaxy to the Milky Way).

I figured someone would call me on that one.

I subscribe to that same school of thought.

I guess the question would be, “Can I see infinitely?” Aside from atmospheric interference, what’s to stop me from seeing “forever”?

AFAIK the most common theory is that the Universe is not infinitely large, but it has no boundaries because it is bent. So, there is no edge; if you had unlimited range of view, you could see the Earth the way it was billions of years ago (to be exact, the number of years it takes for light to travel one round trip). But since there was no Earth then yet, we’ll be disappointed here too.

But can’t telescopes (not the unaided eye) see back in time/as far as the beginning of the non-opaque universe?

i once read that the human eye is only able to see as far as 50 miles. whether or not this is true, i honestly do not know

The sun is 98 million miles away and I can see that just fine. We can see other stuff with the naked eye that is many light years away. There is no inherent limit in how far the eye can see, just depends on how big the thing is that we’re looking at and how much junk there us between us and it to block the view.

Do not look directly at the sun and if you do don’t blame me

Nope. Telescopes only see light that is entering them. The same light is entering your eye at the same time (assume you are standing next to the telescope). Of course, the telescope is far more sensitive so it can ‘perceive’ that which you can’t which is why the telescope is built in the first place. The furthest object I believe has ever been observed here on earth is a supernova some 10 billion light years away. I’ve heard the age of the Universe put at anywhere from about 10 - 15 billion years old so I’m not sure how close that supernova is to the ‘edge’.

Nevertheless you simply cannot see further than light has travelled since the beginning of the Universe. Again, assume the universe is 15 billion years old. Draw a circle around your head with a 15 billion light year radius and that essentially encompasses the ENTIRE universe to you. The Universe itself is bigger than that 15 billion light year circle. Anything beyond that, for all practical purposes, doesn’t exist as far as you are concerned since nothing out that far could possibly have ANY effect upon you whatsoever. It really is as if it doesn’t exist even if it does.

How far you can see depends on many things. If you are talking about standing on a beach and looking over a calm sea then I think the maximum distance you can see is 3-5 miles. If you are looking at something sticking up from the ground you can see further. Indeed, one of the first pieces of evidence that people noticed for the earth being round and not flat was that sailors could see the mast of a ship before they could see the ship itself. I have personally seen the Sears Tower in Chicago from ground level standing over 30 miles away. Now go up in a plane. From 40,000 feet I don’t know how far you can see but I’d wager it is several hundred miles. Look straight up and you can see the moon some 240,000 miles away. Look at the sun and you’re up to roughly 95 million miles and so on. As mentioned the most distant object you can see with the unaided eye is the Andromeda Galaxy which is about 2.9 million light years away (I said 2 million before but I think Squink had it right).

Don’t forget the redshift. The farther away a celestial object is from us, the faster it is moving away from us. The resulting Doppler shift for the farthest objects will radically lengthen the wavelengths by the time they reach us, which would certainly put it out of the wavelengths our eyes can detect.

I never understood this, but I read that it even if the universe were positively curved, it would take light longer to go all the way around than the age of the universe. I beleive that the current thinking is that the universe is flat. This means that the universe is infinite.

Time and expansion. If the universe is infinite and the rate of recession is proportional to the distance, then there past a certain distance, space is receeding at faster than light. We can never get light (or any other information) from these regions. We are surrounded by an event horizon. However it would take light an infinite amount of time to travel from the event horizon to us and the universe was opaque a finite amount of time ago, we would only be able to see as far as when the universe was opaque.

Just for fun so you can get a sense of just how far that is the Andromeda Galaxy is:

17,010,518,400,000,000,000 miles away (that’s 17 quintillion miles…a mighty big number)

maybe we cannot see further than a few millimeters… the distance in the eyes perhaps?

what if all we can see is the back of our eyes?
everything else is like a tv. we assume the distance through visual cues… but not actually seeing that far.

i don’t know…

Wiggum, I think you can see “the edge”, perhaps not the stars, but the blackness… which is really not seeing light at all… so I guess the conclusion is yes, you can not see the “edge” of the universe

That’s what I meant; AFAIK the age of the Universe is estimated at 20 billion years, give or take a few (correct me if I’m wrong), while the diameter is supposed to be in the hundreds of billions light year scale.

I think the curced universe theory is the more popular one currently; the curvation has been proven for small areas (it was possible to detect stars that are set behing other, closer stars and should be hidden, but the space around the close star is bent by the star’s mass, so the light from the distant object can reach Earth. Black holes, too, can warp space a lot, but if this applies to the universe as a whole is undetermined.

Go outside at night and look up in the sky. Notice the stars. Now look at the black stuff in between. You are “seeing” stuff that is extremely far away. It looks black because it is very dim, but if it were brighter it would look like a beige haze.

According to my General Relativity text, in the simplest recollapsing models of the Big Bang, you can see all the way around the Universe at the point of maximum expansion. IIRC, that’s about 30-50 billion yrs. Our universe is currently about 15 bill yrs old. Recent results pretty much rule out a recollapsing universe tho.

Not necessarily. Even a spatially flat universe could have finite volume if it had the topology, say, of a donut. Think of Pac-man - if you go off one side you show up on the other side of the screen.

Don’t say “never”. If you wait long enough, you will eventually see light from those regions. Assuming, that is, that the expansion goes on forever.

Actually not quite. A new theory has been put out speculating a Cyclic Universe. Of course, this is a brand new theory so has a long way to go for full acceptance but at first blush cosmologists seem to think the theory is worth a serious look. However, the upshot of the theory is a never ending repeat of creation.