By Don Lincoln, Fermilab
We know of the size of the visible universe at the moment. It has a radius of about 46 billion light-years. That doesn’t seem to make any sense, since the age of the universe is only about 14 billion years. But it has been expanding, and the most distant spots are moving away from us at the speed of light. This also highlights some complications that one has to take into account. What are they? How does one of it questions the very theory of the big bang? Read on to find out.
The Expansion of the Universe
If the universe currently has a radius of 46 billion light-years, then that’s nearly the distance to the current location of the cosmic microwave background radiation, or CMB, that we see today. But if the universe is about 1,100 times bigger than it was when the light was emitted, then it means that the CMB we see today was emitted at a location 42 million light-years away.
But the expansion means that it took about 14 billion years to travel that distance of 42 million light-year. It’s like a swimmer swimming against a powerful current. And the sphere surrounding the Earth from which we see the CMB today, has stretched from the initial 42 million light-years to the current 46 billion light-years. That means that objects located where the CMB is now will emit light that will never get to us. This all may be a bit confusing, but it’s how it works.
All these numbers are very precise. Our data and our model are both very well-developed, and we know these numbers to incredible precision.
This article comes directly from content in the video series The Evidence for Modern Physics: How We Know What We Know. Watch it now, on Wondrium.
Doubting the Big Bang
Now, it’s possible that one may have heard some claims that might make them doubt some of the numbers. Some of those claims are interesting, while others are completely discredited. One of that which is often mentioned as raising doubt about the big bang. The objection is pretty easy to understand. It stands to reason that the universe should be older than any star in it. Stars older than the universe would be peculiar indeed.
However, there is a star located only 200 light-years away from Earth with the unimaginative name HD 140283. It is an ancient star; in fact, among the oldest ever observed. It is called a Population II star, which means that it contains a larger percentage of hydrogen and helium than other stars. This means it was formed before other stars had time to create elements heavier than helium.
Astronomers tried to work out the age of HD 140283 from what they know about stellar evolution. They came up with an age of 14.46 ± 0.8 billion years. Now, one doesn’t have to be much of a mathematician to realize that the 14.46 billion year age of the star is bigger than the 13.799 billion year age of the universe. This caused some people to question the theory of the big bang, especially those with an anti-big bang agenda.
The Methuselah Star
The unofficial name of this star is the Methuselah star. However, its age estimate isn’t the whole picture. One has to pay attention to the uncertainty in the estimate. If a scientist quotes a number of 14.46 ± 0.8, that means that the true number has a 70% chance of being between 13.66 and 15.26. That 70% number is important, because that means that there is a 30% chance that the actual value is outside that range.
But let’s ignore this 70% number. The lowest possible age for the Methuselah star is 13.66 billion years, which is younger than the 13.799 billion year lifetime of the universe. Thus, it is quite possible that the Methuselah star is younger than the universe. There is no doubt that this particular star is incredibly ancient, but it doesn’t break the theory of the big bang.
If one goes digging, they’ll find that many people try to find ways to upend the big bang and send scientists back to the drawing board, but there are no critics more critical than scientists themselves. They try very hard to make their theories bulletproof. They are constantly testing them and, should a scientist find a chink in the armor, the scientific community will be the first to try to break the theory. However, scientists have turned that level of critique to the big bang, and the big bang survives because of it.
Common Questions about the Big Bang Theory Surviving the Critics
If the universe is about 1,100 times bigger than it was when the light was emitted, then it means that the cosmic microwave background radiation we see today was emitted at a location 42 million light-years away.
Methuselah is a star located only 200 light-years away from Earth with the unimaginative name HD 140283. It is an ancient star; in fact, among the oldest ever observed. It is called a Population II star, which means that it contains a larger percentage of hydrogen and helium than other stars.
It is quite possible that the Methuselah star is younger than the universe. There is no doubt that this particular star is incredibly ancient, but it doesn’t break the theory of the big bang.
