Back to the
Ask An Astronomer page.
On Fri, 2 Apr 1999, Rick wrote:
> Dear Sir:
> The basis of my contention is as follows: The farthest objects so far
> observed are about 12 billion light years away. I read (again, in the
> popular media, but from supposedly reliable sources such as Tim Ferris)
> that that 12 billion light year point is near the origin of the
> universe. HOWEVER, the light took 12 billion years to reach us; the
> objects even at the speed of light retreating from us, would have taken
> 12 billion years to reach the point where the light emanated. This
> gives a minimum age of the universe to be 24 BILLION years. And that is
> assuming the far objects traveled at the speed of light to get there.
> Since that speed is not likely, the universe would seem to be a lot
> older than 24 billion years.
Hello,
This is a common source of confusion, one which took me a while to
understand. In reality, distant galaxies were much closer to us when
their light was emitted then they are today. For example (and these
numbers are just for illustration, they aren't necessarily exact), Light
from a galaxy that was just 1 billion light years away 12 billion years
ago may just now be reaching us. The reason is that the entire universe
is expanding, so as light travels toward us, more space is appearing
between the light ray and us. It is very similar to trying to walk up
the down escalator - it can be done, but it takes a while, because new
steps are constantly appearing! So, the light that we now see from the
edge of the universe has been travelling for at least 12 or 13 billion
years, and it has travelled 12 or 13 billion light-years, but the light
came from galaxies that were very close by 12 billion years ago!
> Just kind of curious if there is an answer to these in your professional =
> circles: what is the universe expanding into?
The short answer is: Nothing. It's hard to imagine, but all of what we
percieve as space is all-encompasing. Still, the space between objects
is growing.
> Was the universe essentially created out of nothing?
There's no good answer to this question - physics breaks down in the
early universe, so any theories as to where the universe came from are,
at this point, speculative and wild guesses.
> Is space really nothing?
It depends what you mean by nothing. If you are talking about matter and
atoms, then space is mostly empty. But space itself is something. It is
full of energy on microscopic scales. Space itself is also measurable -
we can measure a distance between two galaxies, even if there is
"nothing" in between them.
>Isn't the Big Bang theory just a convenient way of defining
> what is ultimately impossible for human beings to comprehend? After all
> "you" set up the equations to conclude what what you want, don't you?
No. The Big Bang theory was developed by scientists who noticed that all
the galaxies in the Universe appeared to be moving apart. So, their
equations were set up to explain this, reasoning that, if things are
moving apart today, at one time they must have been closely packed
together. The Big Bang theory made predictions for things that should be
observable but had not been observed when the theory was created - that
the entire universe should be glowing at a temperature of 3 degrees above
absolute zero, and that hydrogen and helium should have been created in a
certain ratio to each other (that the Universe should be 75% hydrogen and
25% helium). Both of these predictions seemed outlandish when they were
proposed, but they both came true. No other theory has ever been
proposed that can account for these and other observations. It turns
out, that with currently known physics, the Universe can be explained
relatively precisely all the way back to the tiniest fraction (one ten
thousandth of a trillionth of a trillionth of a trillionth) of a second
after the creation of the Universe. So, except for that briefest instant
at the start of the universe, the entire physics of the universe is fully
knowable.
> While experimentation would lead us to believe the velocity of light is
> ultimate, the equations Einstein set up define that to be true; they do
> not prove it to be true.
Every experiment testing Einstein's theories has shown his equations
hold, despite lots of intelligent scientists putting lots of effort into
trying to disprove Einstein. I would be willing to wager obscenely large
sums of money that the speed of light is the fastest velocity obtainable by
ordinary matter in our universe.
I hope this helps some. If you would like to know more on the subject,
Steven Hawking's book "A Brief History of Time" is the clearest
explanations I have found that don't require mathematics.
Thanks for writing!
Sincerely,
Kurtis Williams
Back to the
Ask An Astronomer page.