155. DOOMERS AND THE SECOND LAW OF THERMODYNAMICS
There are three things certain in life: Death, taxes and the second law of thermodynamics!
The second law of thermodynamics states that concentrated energy always diffuses and becomes less dense. Since we are unable to move back in time, we cannot return to the prior energy density. That's the reason we cannot build a perpetual motion machine. You always get less dense energy, there is no escape. Total entropy is constantly increasing.
Doomers have likened this to fossil fuels as oil stores in the ground, stating that as we use them up it's impossible to grow our economy because energy is becoming less dense and we are always on a loser. Well, before you start crying into your cornflakes, it is worth pointing out that the universe is a pretty big place and has been about for billions of years, older than the U.S. constitution itself. So what does this mean for mankind? Several sources of convenient cheap stored energy will run out. BUT there's a heck of a lot of energy out there that can be harnessed, more than we will ever need, and we aren't likely to run out any time soon even though on a macro level, across billions of light years energy is getting less dense over billions of years. We aren't that important!
Take our nearest star, the sun. This beauty produces all the energy we could ever need:
-The energy released in a typical solar flare is equal to more than all the energy used in our entire civilisation. Source
- In fact, there's enough power from the sun hitting the Earth every day to supply all the world's needs for energy 10,000 times over. Source
Some of that energy creates the wind:
One study also estimated the amount of global wind power that could be harvested at locations with suitably strong winds. The authors found that the locations with sustainable Class 3 winds could produce approximately 72 terawatts and that capturing even a fraction of that energy could provide the 1.6-1.8 terawatts that made up the world's electricity usage in the year 2000. A terawatt is 1 billion watts, a quantity of energy that would otherwise require more than 500 nuclear reactors or thousands of coal-burning plants. Converting as little as 20 percent of potential wind energy to electricity could satisfy the entirety of the world's energy demands, but the researchers caution that there are considerable practical barriers to reaping the wind's potential energy.SourceSome of that energy leads to evaporation and rains depositing water on high ground that can be used for hydro energy (currently 17% of world electricity -- 99% in Norway, 57% in Canada, 55% in Switzerland, 40% in Sweden, 7% in USA).
This excludes other forms of energy that can be harnessed, such as Biomass, Wave, Geothermal and Nuclear.
Take nuclear power:
At the present rate of use, there are 50 years left of low-cost known uranium reserves - however, given that the cost of fuel is a minor cost factor for fission power, more expensive lower-grade sources of uranium could be used in the future  . Also, extraction from seawater  or granite is possible. Another alternative would be to use thorium as fission fuel in breeder reactors - thorium is three times more abundant in the Earth crust than uranium .Of course figuring out how to harness this energy in a cost effective way is another matter. Nevertheless we are never going to run out of energy to harness during the expected life of this planet, so don't panic yet.
Current light water reactors make relatively inefficient use of nuclear fuel, leading to energy waste. More efficient reactor designs or nuclear reprocessing  would reduce the amount of waste material generated and allow better use of the available resources. As opposed to current light water reactors which use Uranium-235 (0.7% of all natural uranium), fast breeder reactors use Uranium-238 (99.3% of all natural uranium). It has been estimated that there is anywhere from 10,000 to five billion years worth of Uranium-238 for use in these power plants . Breeder technology has been used in several reactors .
Proposed fusion reactors assume the use of deuterium, an isotope of hydrogen, as fuel and in most current designs also lithium. Assuming a fusion energy output equal to the current global output and that this does not increase in the future, then the known current lithium reserves would last 3000 years, lithium from sea water would last 60 million years, and a more complicated fusion process using only deuterium from sea water would have fuel for 150 billion years. Source