Tuesday 10th May 12:08 pm
How much energy does it take to build a solar system?
Tuesday 17th June 2014 2:36 pm
Last time, I talked about just how many Earth-like planets could be stuffed into a solar system. It turns out to be about 60.
Just to keep it simple, I glossed over a few problems. For example, I skipped over the possible destruction of the atmosphere of these Earth-like planets, as a result of their being so close to the powerful solar wind of a red dwarf.
Nor did I discuss the problems that can happen when you have similar-sized largish bodies (such as a pair of Earth-like planets) dancing around each other. These problems include massive tides, overwhelming tectonic plate activity, huge volcanism, rather long days of a few weeks or so, and more issues like these.
So while we’re sticking to the big picture, let’s go one step further, and work out if we could ever build such a solar system.
Now the very first thing to realise is that we are going to need energy — lots and lots of it.
Back in prehistoric times, we could use only biological or animal energy. So we used the sweat of our brow, or that of a large animal.
The first real breakthrough came when we started using fossil fuels. They are incredibly concentrated in energy. A barrel of oil contains about 159 litres of liquid. Translated to human terms, a barrel of oil holds the potential labour of a human working a 40-hour week for about four-to-ten years. At around $100 a barrel, that’s a bargain. But if you are going to shift planets, that’s not enough.
So let’s look at the Kardashev scale, which was first proposed in 1964 by the Soviet astronomer Nikolai Kardashev. He defined a civilisation, not by its art or technological achievements, but by how much energy it could use.
A ‘type I civilisation’ would use all of the energy that its local star would send towards its home planet. At our current rate of increase of power consumption, we will become a type I civilisation in a century or two. The Sun dumps about 1016 watts of energy on our planet — that’s 10 million billion watts. If we want to generate that kind of power, we would have to do huge amounts of nuclear fusion — and burn about 280 kilograms of hydrogen (turning it into helium) each second.
That’s a lot of power — but it’s not enough to assemble planets from smaller asteroids, or move them around at our convenience.
No, we would have to advance to what Kardashev defined as a ‘type II civilisation’. We would have to be able to generate and control as much power as our Sun radiates in all directions. That’s around 1026watts — or 100 trillion trillion watts. To generate that kind of power, our Sun burns about 600 million tonnes of hydrogen each second. (As our current rate of power consumption increase, we will probably get to be a type II civilisation in a few thousand years.) But even that would not be enough.
We would need to become a ‘type III civilisation’. According to Kardashev, that would mean being able to generate and control the amount of power put out by our entire Milky Way galaxy, with its hundreds of billions of stars. If you want a number, that’s around 1037 Watts, or 10 trillion trillion trillion watts.
Now I’m quietly confident that we will get through our current crisis with global warming — although it will be unnecessarily expensive, because we waited so long to do anything about it. But once we get past this climate crisis, I believe that one day we humans will control enormous energies. The jump we made from controlling the power of a horse, to controlling the power of fossil fuels, will seem puny.
I suspect that our progress on the Kardashev scale will not be smooth and linear, but will go in sudden jumps.
For example, in 1905 we had no idea that relativity would give us GPS or sat-nav. In 1972, we had no idea that the search for black holes would give us Wi-Fi. In 100 or 1000 years from now, what will our ancestors do with dark matter or dark energy? In 5000 years, will we be able to dump a star into a black hole and capture the power from the photons emitted from its accretion disc?
We know that enormous energies are there, but today, we have absolutely no idea of how to get access to it. But what about our grandchildren, or their grandchildren, and so on?
Maybe they will be able to use starlight and really let it shine on their world…
This blog first appeared on Dr Karl's Great Moments in Science
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