Here we go again! This is me procrastinating on writing something practical to take time to write something fanciful. And if there is one thing I love writing about more than anything, it is blurring the line between science fact and fiction.
Everything we have ever built was made from materials lying around on Earth, which is convenient since we need air to breathe and gravity to give us a sense of up and down. Eventually, we started to harvest the energy that rains down on us from space, specifically our sun, Sol. If there is one thing we can see coming down the pipe, it is the finite amount of resources actually on the Earth. The harder we wring the cloth for every drop of oil, or natural gas, or coal, we do more to destabilize the environment. Oil spillage, hydraulic fracking, and mountain topping are the most egregious examples, but even burning these fossil fuels are doing their damage over the decades. Great minds over the past century have been urging us to switch over to solar power, and even demonstrated mathematically that there is so much more juice for our machines raining down on even just our deserts.
In my opinion, even this is thinking too small. We have been able to learn a lot about the universe by looking out into space, in the last fifty years we have learned a good deal about our solar system, and we know quite a bit about how our star works. In brief, it has several layers just like the Earth does. Starting from the center, the core extends out a quarter of the way and is the place where the fusion happens; hydrogen gets smashed into helium and gives off lots of energy. From the core out seven-tenths of the radius is the radiative zone, where the pressure is too high to allow convection but too low for fusion. The energy simply radiates out to the next layer, the aptly named convection zone. This is where the pressure drops and the plasma can circulate like our wind and water currents, moving the energy out to the surface of the sun. Now we’ve reached the sun’s atmosphere; the photosphere, chromosphere, and finally the corona. It is that last one that is most important, because it extends out 15 million kilometers and is stupendously hot, as hot as the core.
In thinking about the sun and just how hot it is, our usual temperature scales fail miserably to grasp the situation. Proposed in 1724, the Fahrenheit scale is based on the freezing point of brine, a specific formulation of salt water, and was subsequently modified by several others to make it more appealing. It was replaced with the Celsius scale a few decades later, in which 0 was freezing for water and 100 was boiling. Such simplicity made it the international standard for almost two centuries. However, Lord Kelvin wrote in 1848 about the need for an ‘absolute temperature scale’, where zero corresponded not with the freezing point of water, but with the absolute minimum possible temperature, absolute zero. Each degree on the scale was identical to the Celsius, which made conversion between the two scales very simple. The scale works very well for all situations, especially for astronomical temperatures. Here are some temperatures, in units of Kelvin, of interest:
- 0 – the temperature of a perfect vacuum, devoid of all energy and matter
- 0.000 000 000 100 – the lowest temperature artificially generated
- 1 – lowest temperature observed in nature, of the Boomerang Nebula
- 2.73 – average temperature of space due to cosmic radiation
- 273.15 – freezing point of water at 1 atmosphere
- 373.15 – boiling point of water at 1 atmosphere
- 3 473 – temperature of a hydrogen gas flame, the hottest combustion flame
- 5 778 – surface temperature of the sun
- 28 000 – temperature of a lightning bolt
- 16 000 000 – temperature of the sun’s core and corona
- 10 000 000 000 000 – temperatures generated by the CERN collider
Exactly what ‘heat’ is has been the subject of scientific research for a long time. The ancient cultures believed that hot was a property two of the four primordial elements, fire and air. After the industrial revolution, the steam engine was a very important item of research. Sadi Carnot published in 1824 his seminal work, On the Motive Power of Fire, which many regard as the starting point of thermodynamics and our mechanical understanding of how heat works. Basically, everything is made up of atoms and molecules, and these molecules are constantly in motion. How much motion determines the state of matter; well ordered, slow moving collections of molecules we call solids, and chaotic, fast moving collections we call gases. The ‘heat’ is a measure of how fast the particles are moving. Now, lot’s of things should start falling into place. This explains why we cannot ever get to absolute zero, because “motion never stops”; the electrons are always flying around the nucleus. Also, temperature could be viewed as the ‘average energy density’ of molecules (higher temperature, more energy), so even the vacuum of space wouldn’t be absolutely zero since there is plenty of starlight flying all around. One would have to move faster than the speed of light and then move beyond the horizon of the universe to areas untouched by light to find a perfect vacuum; even then, the act of measuring the temperature raises it above zero (thanks, Heisenberg).
So now let’s bring back a little bit of fiction. How could we benefit from all of this? Well, it helps us understand what it means for the corona to be 16 million degrees Kelvin. It’s not that the hottest fire mankind has ever witnessed is hovering just over the sun, but rather it means there is so much energy being flung off into space that it registers high on our thermodynamic scale. Think of it as being that much closer to the lightbulb; if you thought the Sahara got a lot of sunlight, think again. Armed with technology that allows us to harvest the sun’s energy and tapping into the massive amount of raw materials floating around in our solar system, we have everything we need to start a theoretical new existence. Enter the Dyson Sphere.
The mathematician Freeman Dyson first proposed the idea after being inspired by Olof Stapeldon’s work of fiction, Star Maker. The idea is that advanced civilizations who exhaust all sources of energy, resources, and land available on their home planet would naturally strike out into space. Where would they go? Well, assuming they could perfectly recycle all of the air, water, and other elements essential for life, they could set up shop anywhere; on any moon, planet, or even comet. But if their source of power is the sun, they would most likely take up living in orbit around their star. Thus the ‘sphere’ isn’t really a large, physical ball made out of solar panels, but rather a description of the zone that would be safe to inhabit. Dyson himself predicted the first forms would be more like independent space stations orbiting a star; space gondolas over the sun. If the civilization gets very good at it, then maybe the stations could all link up and connect into a grand sphere in the first sense of the word.
If we wanted to pull this off, hypothetically, then the habitats we create would most likely be of very high population density-at first anyways. Well, we would need to build these space gondolas high enough so solar flares and intense corona don’t instantly fry the occupants. I just picked a value of half again as high as the corona extends from the surface of our sun, high enough to be beyond the reach of solar flares. At this distance, the solar energy flux is 60 750 watts per square meter. Compare that to the value at the surface of the Earth, 1 366 watts per square meter. Now if we look at New York City as an example of close quarters living, the average person uses about 96 square meters of land, and the average American uses about 10 000 watts of electricity. For our Dyson sphere, every 96 square meters would absorb 5 832 000 watts, enough to stack 583 people on top of each other. Furthermore, our ‘sphere’ at this height would have a surface area of 4.73 x 1022 square kilometers. So there is enough room and board for something like… 2.87 x 1029 people; or 287 billion billion billion humans. Try to overpopulate that! I’d bet the odds that we will be able to set up shops around other stars long before that even becomes a problem again.
Just imagine your descendants’ possible future. They will wake from their slumber in orbit around the sun and climb into their ship that had been charging all night. From there they might visit any local destination within the solar system. Maybe the mining operations in the asteroid belt, or water harvesting from Europa, a moon of Jupiter. Maybe the destination is more exotic, one of the distant stars in the galaxy. After appropriate changes to the solar absorption panels to match the new star and maybe fitting the gondola with some extra boosters to get right up to the speed of light. When moving this fast, special relativity and time dilation predict that a human could travel the full length of the universe in a single lifetime, but when they return to Earth billions of years will have passed, making this trip essentially one way. We would no longer be bound to planets, anything in the universe becomes ours for the taking, and our human love of exploration will take over. It all starts with taking up residence around our mother star, in the region known as the Dyson sphere.