Post Author: Bill Pratt

Continuing from the first post on this topic, we will look at two more methods that physicists and astronomers use to determine the age of the universe.  Again, this information has been gathered from Hugh Ross’ A Matter of Days.

The third method physicists use to calculate the age of the universe is to measure the age of stars throughout the universe.  Stars are simple objects, composed of 100% gas, that burn through the process of nuclear fusion, which, according to Ross, is very well understood and experimentally verified.

Because the process of stellar burning is so well understood, the physicist or astronomer can determine the age of a star if he knows the mass, color, and brightness of the star (all characteristics that can be measured from earth).  From this data, the astronomer can know how long the star has been burning, which places a boundary on how old the universe must be (it can’t be any younger than the oldest star).

The fourth method physicists use to calculate the age of the universe is to measure the relative quantities of radioactive isotopes in the universe.  Radioactive isotopes are only produced by supernovae, which are supergiant stars in their last stage of burning.

It turns out that radioactive isotopes decay at rates (half-lives) that are well understood.  Uranium and thorium, for example, have half-lives of billions of years.  Since we still find uranium and thorium in the universe, we know that the universe cannot be so old that these isotopes had completely decayed out of existence.  That sets an upper limit of a few hundred billion years.

On the other hand, those isotopes with half-lives of millions of  years or less (e.g., plutonium, neptunium, technetium) cannot be found on the earth, so we know that at least a billion years have gone by for them to have disappeared.  Since astronomers know how much of these isotopes were produced by ancient supernovae, and they know the decay half-lives, by measuring the amounts of these isotopes in existence today, they can calculate how much time has passed since the first supernovae produced the first isotopes.  Obviously the universe must be older than this.

Summary and Conclusion

I hope you were able to follow, at least at a basic level, these four methods.  Ross claims that there are many other independent methods that have been used to calculate the age of the universe, but that these four are the most simple for lay people to understand.  What strikes me about these methods is that they rely on different and independent measurement techniques, but they all arrive at the same answer for the age of the universe – around 13.7 billion years.

It’s easy to attack one measurement technique as being inaccurate, but when four independent methods give you the same answer, you need to pay attention.  And remember, it’s actually more than 4 techniques.  The laws of physics used to date the universe are very well understood and experimentally verified to a great degree of precision.  To dismiss all of these independent measurements as erroneous betrays a lack of understanding of physics and mathematics.

If you find yourself still questioning these findings, ask yourself why.  The age of the universe does not at all undermine Scripture.  Whether the universe is 13.7 billion years old or 6,000 years old has no bearing on the truths taught in the Bible.  As Christians, we are to seek out the truth, no matter what it may be.  The true findings of science will never the contradict the Word of God, so engage with science and enjoy the discoveries that lie ahead of us.  We have nothing to fear!!

Post Author: Bill Pratt

Some in the evangelical community dismiss the science that shows the universe is old (almost 14 billion years), and I think partly because they never considered the reasons why scientists make this claim.

I am not a physicist or an astronomer, but I am an electrical engineer, so I had to take physics classes in college and gain an understanding of physics in order to practice electrical engineering.  I am going to present some reasons the universe is old, but I cannot get into the details of it.  These reasons are taken from Hugh Ross’ book, A Matter of Days.  I am hoping that this post, and the next, will spur some of you to do more research on the topic.

The first method physicists use to calculate the age of the universe is to measure the expansion rate of the universe.  The universe is growing larger (like a balloon expanding by someone blowing into it), and if we can measure at what rate it is growing, we can calculate how long ago the universe came into existence.  We can mathematically reverse the expansion until the universe reverts back to a singularity, a point so small the human eye cannot detect it.  This is the beginning of the universe.

The way the expansion is calculated is by measuring the distance from other galaxies to us, and observing how fast these other galaxies are moving away from us.  If we know the distances and velocities of enough galaxies, we can calculate the expansion rate of the universe, and thus the age of the universe.

The second method physicists use to calculate the age of the universe is to measure the cosmic background radiation temperature.  When the universe came into existence, it generated a lot of heat!  Ever since that creation event, the universe has been cooling down as it ages.

When we measure the cosmic background radiation (“take the temperature” of the universe), the readings indicate that the temperatures all around us are about -455 deg F (only 2.725 deg C above absolute zero) and vary little – less than 1 part in 10,000.  Given the geometry of the universe and these temperature readings, physicists can calculate how long the universe has been cooling, and thus the age of the universe.

In the next post, we will look at two more methods for determining the age of the universe.  I hope you’ll stick around to learn about them.