Do you feel yourself an insignificant speck when you contemplate the immensity of the universe and are drawn to make comparisons? Well, so you should.
How big is the universe? This is a complex question depending, among other things, on whether you mean ‘known universe’ or ‘observable universe’.
‘Known universe’ means the distance to the furthest object we have seen to date. That object is about 28 billion light-years away from us. We can assume this to be the radius of an immense universe if you want, but doubtless more distant objects than this will be seen in the years to come.
‘Observable universe’ means where the furthest ‘edge’ of the universe is moving away from us at the speed of light in a vacuum. Einstein tells us no material substance can move away from us faster than this, so that, beyond this ‘edge’, there is effectively nothing (some would debate this). Calculations put this edge at about 46 billion light-years from us.
[The ‘light-year’ is a unit of distance NOT of time. It is the distance that would be travelled by light in one Julian year of 365.25 days.]
Alright. How fast does light travel? Answer: 299, 792 km/sec rounded to the nearest whole number, or near enough (say) to 300,000 km/sec. That’s insanely fast.
Doing the calculations, a light-year comes in at approximatey 10 trillion kilometers. And the universe has a radius of either 28 or 46 billions of these, depending which measure you choose to take.
Can you get your mind around these numbers?
Since we now have a putative radius for the universe, we could (if we were were so inclined) calculate its volume. This would put us in the position where we could calculate the equivalent number of Olympic-size swimming pools!
Let’s stick a little closer to home. The nearest star to us (bar our own sun) is the faint speck we know as Proxima Centauri at 4.25 light-years away. This means that, if we were able to travel at the speed at light, it would take us 4.25 years to get there. Alternatively, if we saw Proxima Centauri in the sky (the naked eye is not adequate for this purpose, so it would have to be through a telescope), we would see it not as it is now, but as it was 4.25 years ago. That’s how long it takes for the light emitted by Proxima Centauri to reach us.
Or take Sirius, the brightest star in our night sky. Please let’s not count planets! The so-called dog star is a mere 8.6 light-years from us. Stars such as Sirius are our near neighbours. Sirius appears to us as bright as it is because it’s so close to us!
If we talk ‘intrinsic brightness’ rather than ‘apparent brightness’, there are much brighter stars than Sirius in our night sky. They have names like Aludra and Wezen, and are (or perhaps were) thousands of light-years away. We see them now as they were thousands of years ago and, for all we know, they may not actually exist anymore.
As a consequence of the immensity of the universe, distance and time become inextricably intertwined. Cosmologists, for convenience, often think of time as the fourth dimension of a construct called space-time.
Does all this immensity make you feel insignificant? Well, on this scale I’m afraid to say you are just that. Whether you like it or not, you have to live with the fact. It certainly is bad news for those of us who like to big-note themselves.
But for those of us who like to fly under the radar, it suits just fine.