He indicated that if energy usage continued to increase by 2.3% per year and all used on earth then the temperature would in 930 years be equal to the surface of the sun. Obviously if you have that much power you have to spread out beyond the earth. It would be 31 doublings of the energy that we had now. 2 billion times more.
A Dyson shell has 550 million times the surface area of the Earth. The surface area of the earth is 510,072,000 square kilometers. If some caveman made some projection that we could never use our current level of energy (18 Terawatts) because it was all used on the surface of the small island that he lived upon the temperature would be too high is the same argument that Tom Murphy made.
Here I summarize some of how to do get to Kardashev level two.
Getting to Kardashev level two can be easy.
If we end up with a lazy Kardashev level two. Other solar systems make close (within about one light year) passes of our solar system every million years or so.
If humanity chooses to stop or slow growth at Kardashev level two that will a choice for them at that time. A Kardashev level two civilization can then migrate over to other solar systems and keep splitting to get to Kardashev level three.
We can get to 1-10% of Kardashev level one by staying on the planet and leveraging factory mass produced deep burn nuclear with ocean uranium supplies and using aerostat directed solar. Bubbles for collecting and focusing solar power make a Dyson swarm very light weight.
I have written plenty of achieving the level of about kardashev 1 and then 2.
Those are the usual terms for
all solar energy for one planet – Kardashev level 1
all solar energy from one star – kardashev level 2
So getting closer or fully up to Kardashev level 1.
Factory mass produced nuclear fission with deep burn closed fuel cycle and accessing the uranium and thorium in the ocean. This can be done without developing any space capability and lets you have a lot of power for a long time until you can get off your collective asses and into the solar system.
A society using current energy could last 5 billion years at current energy levels. If you are earthbound the sun expands into a red giant at that point and if you were stuck with crappy technology then all of humanity is done at that point. Plenty of other astronomical bad stuff can happen over the course of a billion years like getting hit with a big asteroid. So the static technology plan is always hosed on those time scales.
A yottawatt civilization would be roughly equivalent to a Kardashev 1.75 civilization. Fission, fusion and space solar can get a civilization to Yottawatt for long periods.
Hall Weather Machine
A far better architecture for capturing the solar energy that hits the earth is the Hall weather machine.
The Hall Weather Machine is a thin global cloud consisting of small transparent balloons that can be thought of as a programmable and reversible greenhouse gas because it shades or reflects the amount of sunlight that hits the upper stratosphere. These balloons are each between a millimeter and a centimeter in diameter, made of a few-nanometer thick diamondoid membrane. Each balloon is filled with hydrogen to enable it to float at an altitude of 60,000 to 100,000 feet, high above the clouds. It is bisected by an adjustable sheet, and also includes solar cells, a small computer, a GPS receiver to keep track of its location, and an actuator to occasionally (and relatively slowly) move the bisecting membrane between vertical and horizontal orientations. Just like with a regular high-altitude balloon, the heavier control and energy storage systems would be on the bottom of the balloon to automatically set the vertical axis without requiring any energy. The balloon would also have a water vapor/hydrogen generator system for altitude control, giving it the same directional navigation properties that an ordinary hot-air balloon has when it changes altitudes to take advantage of different wind directions at different altitudes.
By controlling a tenth of one percent of solar radiation is enough to force global climate in any direction we want. One percent is enough to change regional climate, and ten percent is enough for serious weather control.
The surface are of the earth is 510 trillion square meters.
So getting to 0.1% coverage is 510 billion square meters.
There is mylar that is 2 microns thick and weighs about 2.4 grams per square meter. Office Paper is usually 80 grams per square meter.
There is plastic sheeting with 0.3-0.9 micron thickness and weights of 0.54 to 1.2 grams per square meter.
US plastic film demand was expected to be about 7.3 million tons in 2012
So if you could achieve large scale production (equal to 1% of total US plastic film production in 2012) of 1 gram per square meter balloon sheeting with a diamond surface treatment and the other parts of the system there would be 73,000 tons of weather machine produced. This would cover 73 billion square meters. In about 8 years, one would be able to produce a 1% coverage Hall Weather Machine.
The production system would be a more advanced version of bubble wrap production. Each bubble would be functionalized and perhaps laser cut into separate balloons. Rapid printable electronics would probably be the best way to get the solar cell and GPS components into the bubble/balloon. The printable electronics would need to be scanned onto the surface of the sheet, before the top layer is attached.
With better than todays nanotechnology one could easily produce a more advanced version of the hall weather machine. It is a weather machine and a means to use not that much material to get to Kardashev level one.
Weather machine Mark I – many small aerostats—a hydrogen balloon—at a guess an optimal size is somewhere between a millimeter and a centimeter in diameter that have a continuous layer in the stratosphere. Each aerostat contains a mirror, and also a control unit consisting of a radio receiver, computer, and GPS receiver. About 100 billion tonnes of material with regular technology and 10 million tons with more advanced nanotechnology.
Once you are approaching kardashev level one or even at ten times the current world economy then funding a true space industry in the solar system is trivial
If your nanotechnology is at this level then making spaceships and sending nanofactories to Venus and asteroids would be relatively simple. It would be about twenty million tons of material for the mirror bubbles and converters for each earth scale energy system. Then the electricity has to be transmitted and distributed to where it needs to be used (a super-grid which could be wireless)
Two billion of those systems turns humanity into a Kardashev Type II civilization.
Producing large bubbles in space is something that looks very doable.
The bubbles would be set up to focus solar energy to make the collection of solar power easier.
The most interesting Nasa Institute Advanced Concepts (NIAC) study released from the March 2007 meeting is Devon Crowe of PSI corporation for making large space structures from bubbles that are made rigid using metals or UV curing.
A single bubble can be 1 meter in earth gravity, 100 kilometer in low earth orbit or 1000 kilometers in deep space. Foams made of many bubbles could be far larger in size.
Metal can be evaporated to coat the inside of the bubble for reflective sails and telescopes.
I also think that GDP growth will get faster. So we will get to (or need to get to) Kardashev level one and level two far sooner than your 2.3% projection.
Kardashev Level 2+ civilizations could manage their stars
The list of nearest stars contains all known stars and brown dwarfs at a distance of up to five parsecs (16.308 light-years) from the Solar System. In addition to the Solar System, there are another 51 stellar systems currently known lying within this distance. These systems contain a total of 61 hydrogen-fusing stars and 9 brown dwarfs
Giant stars can produce 100 to 1000 times the energy output of the Sun.
Another assumption made by Tom Murphy is that the Kardashev 2 civilization would not start heading out and managing a stable of solar systems before the time when they would start to max out on the energy demands of one star. They have dozens of stars within 17 light years and hundreds to thousands within 100 light years. Some already are producing at higher rates and other stars could be easily (for a type II civilization have production increased.)