So how old is the Universe, the playground of our existence?
Just a small portion of the hundreds of billions of galaxies littering the universe, containing a few 100 billion stars each
The answer can be quite controversial, and depends heavily on what model of the universe you prescribe to, the most widely accepted model is that of an expanding universe. This is to say a universe that started off as a point on a sub-atomic scale, and expanded to its current dimensions within a certain amount of time, that time is thought to be around 13.7 billion years.
Although there are endless equations and I am sure loads of different methods to come to the above conclusion, I have included here only 3 that you need to competently say you know, how we know, that the universe is about 13.7 billion years old.
The Hubble constant (Edward Hubble)
Is a measure of the expansion rate of the universe. If galaxies are moving away from us at a certain speed, then rewinding this movement back to when everything that is was in one tiny space, we will get the age of the universe.
We can tell what speed a galaxy is moving away form us by invoking the Doppler effect, the same effect we find for sound.
The Doppler effect is the process whereby light shifts to longer wavelengths depending on the speed at which the galaxy/star is moving, if they are moving away from us, their light will “shift” towards the red end of the spectrum.
There are some problems with this, one being that it does not take into account a changing rate of expansion. Scientists now believe that something called “dark energy” might be causing an increased rate of expansion.
Globular clusters are a dense collection of roughly a million stars, densely packed together, their proximity to each other means that all the stars in this cluster were created around the same time, and so we can use them as a kind of universal clock.
A star such as our sun takes around 9 billion years to burn through its fuel, a star twice as dense will take only around 800 million years to burn out, whereas a star which is half as dense could burn for 20 billion years.
The oldest globular clusters we can “read” tell us that the universe is between 11 and 18 billion years old.
The Cosmic microwave background radiation
The CMB is a “cloud” of energy visible everywhere we look in the universe, it is left over from the very early days of expansion, when the universe was (to quote “The Big Bang Theory) in a hot, dense, state, and is only currently explainable by the Big Bang Theory, .
It has moved from a high energy state to its current low energy one over the 13.7 billion year span of the universe. About 2% of the static you see on a badly tuned TV station is the result of this radiation.
By reading detailed maps of the CMB, we can measure the energy density and composition of matter in the universe, and rewind this back to see how it has evolved, and how long it took to reach its current state.
These are the methods we use to find out how old the universe might be, but remember, they are by no means fail proof, and one day we might find out a new bit of info which allows us to refine these theories.
And that’s it for How Old is the Universe
So this is a basic, by no means comprehensive breakdown of how old the universe is, and how we know how old it is. Things in science change all the time, and there are much more involved and complicated ways to explain and say what I have said above, but I think you get the gist of it.
If anyone knows or wants to add something to the above, please let me know. I am always happy to refine the things I think I know.