Expert: Courtney Seligman - 8/17/2011

Question
From what I know (which is probably wrong), the way we have discovered that the universe is 13 billion years old is because when we look into the night sky, that how old the furthest light we can see is. If this is true, is it not possible then that the universe is older, and that there is light further away, that has simply yet to reach us?

Also, i'm not sure if this is against any rules, but I have one more question. According to theory, there might be an object out there called a white hole, which is basically a black hole in reverse, shooting out matter into space instead of sucking it in. Now I know this is only a theory, but do the people who came up with this theory have an explanation of where the matter has come from? Matter can't just come from no where can it?

Answer
In its simplest form, the age of the Universe is determined from the rate of its expansion, compared to the speed of light. If the rate of expansion was constant with time, then you could simply measure how far away things really are (though such measurements are anything but simple), and compare it to their recessional velocity (as calculated from their "redshift"). The ratio is the Hubble "constant" (so-called because it nearly is constant, over vast distances). Dividing that constant into the speed of light tells you how far away things would have to be, to be receding from us at the speed of light. In a Universe expanding at a constant rate, that would be numerically equal to the age of the Universe.

Let's suppose the Hubble constant was 70 km/sec/Mpc (which is very close to the correct value, and is a nice round number). Then the size of the Universe would be (rounding off the speed of light to a nice round number as well) 300,000 km/sec divided by 70 km/sec/Mpc. The km/sec cancel, and the result is that objects 30,0000 / 70 = 4,286 Mpc away would be receding from us at the speed of light. Converting to light years (that is, multiplying by 3.26 Mly / Mpc) yields 13.97 billion light years. That would be the age of the Universe, if all the assumptions above were correct.

In reality, the Universe has expanded faster at some times, and slower at others (as determined from a comparison of actual distances to recessional velocities), so the age is estimated at closer to 13.7 billion light years; but the idea is the same. Only the calculations are more complicated.

Why is this the age of the Universe? Because if things at various distances have been moving away from us at their various rates for that long, they would have all been "right here" (or more accurately, they would have all been in the same place, wherever that was; but since we would have been there too, it would still be "right here"). That situation, in which everything in the Universe was in the same place at the same time, represents the Cosmic Fireball, or the start/end of the "Big Bang". Any information about whether anything existed prior to that time would have been destroyed by the conditions at that time, so it has been presumed to be the logical "beginning" of the Universe, since the Cosmic Fireball theory was first proposed, about 75 years ago.

Of course, since then much work has been done on the theory, and we now have reason to believe that this really was the beginning of the Universe, in every sense of the phrase, because assuming it was, we can make certain predictions about the appearance of the Cosmic Microwave Background, which all appear to fit what we observe, to an accuracy better than our ability to observe them. Whether those theories and predictions are actually correct is a matter of debate, but most cosmologists accept them as if written in stone, and argue more about the details of various versions of the theory, than whether the basic idea is right or wrong. So though there is a (very small) variation in estimates of the age of the Universe at the current time, the general idea is felt to be correct.

Now, as to whether there could be things that are so far away that their light simply hasn't had time to reach us. In discussing the theory of the age and appearance of the Universe, one way to explain it to beginning students in astronomy (as I did for 40 years) is to imagine that the Universe looks the way it does simply because things further away than its age are too far away for their light to have reached us. So your presumption makes perfect sense, and could be perfectly correct. However, that argument only works if you assume a static Universe, in which the distances of things don't change, and it is only their distance that prevents their light from reaching us. In an expanding Universe, things further away than the age of the Universe will never be seen by us, because the empty space between us and them is expanding faster than the speed of light. That sounds like it violates that speed-of-light-limit, but that only applies to how fast things can move through a given part of space. If each part of space is expanding at a certain rate (the Hubble "constant", more or less), than at a distance equal to the "age" of the Universe, the total space between here and there is expanding at the speed of light, and light from such regions has needed the entire age of the Universe to reach us, not because they were far away when their light left them (in fact, at that time they were actually very close to us), but because their light hardly made any headway, during the time that it was nearly as far away as they are, and the space between us and them was expanding at nearly the speed of light. For objects even further away, the space between us and them is expanding at more than the speed of light, so their light is getting farther and farther away from us, despite its light-speed movement through the space it is currently traversing. In other words, no matter how long we wait we will never be able to see anything that is farther away than the age of the Universe. That is how we define the "observable" Universe, which represents things close enough that their light is getting closer to us, as compared to the "real" Universe, which includes things so far away that their light is actually getting further from us.

(I hope the above is reasonably clear, and that you will forgive the simplifying assumptions made in writing it, as discussing the complications that cosmologists have to deal with because things are actually a little more complicated than the simplifying assumptions would imply would not change the result much; they would just make the discussion closer to "as clear as mud". But if any part of it needs further clarification, please let me know, as I'd like it to be as clear as possible.)

As to white holes. In the earliest theories of how black holes work, certain simplifying assumptions were made, to make the math easier to do. Those simplifying assumptions led to the idea that objects falling into a black hole might be able to avoid falling into the singularity in the center of the black hole, and eventually emerge somewhere else. That "somewhere else" would be seen by observers in that place as a "white hole", and the "connection" between where things fell into a black hole here and a white hole somewhere else is a "wormhole". Such things are very popular science fiction vehicles for overcoming the speed-of-light limit to space travel in sci-fi "westerns" (most space operas being basically westerns set in space; so that the recent movie "Cowboys and Aliens" isn't really much different than most other sci-fi shoot-em-ups, save for the details).

Unfortunately, the basic idea of white holes requires that things that fall into the black hole can avoid falling into the singularity. And although for the theoretically perfectly simple black holes used in early calculations such a thing is possible, real black holes are "messy", and there is no real way for something to fall into a black hole without running into the singularity. As a result, once things go in they can't come out, and white holes (and wormholes) are impossible. They still exist in sci-fi and in TV "documentaries" which are basically wishful thinking presented in a pseudo-scientific way, but they cannot exist in the real world (or perhaps more accurately, in the real Universe).

So if black holes were as simple as early theoretical versions, white holes could exist, but the stuff coming out of them wouldn't be coming from "nowhere". It would be stuff that fell into them "elsewhere". And in reality, they can't exist; so where the stuff would come from is "moot" (that is, since white holes can't exist, where their stuff might have come from if they could have existed is irrelevant). It's sort of sad, because it would be interesting if they could exist; but whether they can or not doesn't prevent anyone from writing fiction based on the idea, so a host of space operas continue to use the idea to enable hopping and bopping from one place to another without worrying about the vast amounts of time that would really be required to get there.

(And again, even though such things can't exist, if you'd like more discussion of them or similar ideas I'm perfectly happy to oblige, as I write fiction myself, and have no problem with bending the laws of nature to fit the plot. It's only when I write about the real world that I feel I have to stick to the facts.)

Finally, as seems to be all too common a case for my recent answers, I must apologize for not going back and proofreading the above, but your question didn't come in until late last night, I didn't get to bed until even later, and my eyes are starting to glaze over; so I need to go back to bed, and the only reason I'm writing this answer right now is that I don't want you to have to wait until late this afternoon (or, given what I have to do this afternoon, more likely this evening) to receive my reply.