Fermi’s Paradox

If technologically advanced, star-faring civilizations really were common, they should already be everywhere, including Earth.

The logic goes by this: nothing can travel faster than speed of light. Dividing distance (the size of Milky Way galaxy) by speed (one-tenth the speed of light), it would take hundreds of thousands of years to hop across star systems. It may sound like a very long time, but the galaxy is 13.6 billion years old. Relative of age of the galaxy, any space-faring species should be able to reach anywhere in the galaxy in the cosmic blink of an eye.

Drake’s Equation

Drake defined advanced and technological as possessing radio telescope that could be used for interstellar communications.

N = R_* f_p * n_e * f_l * f_i * f_c * L

Here, R_* equals number of stars forming each year, f_p fraction of stars with planets, n_e number of planets per solar system with a suitable environment, f_l fraction of planets where life forms, fraction of planets where life evolves to intelligence, f_c fraction of planets where they go onto creating technological civilizations, L average lifespan of those civilizations.

We know for certain f_p = 1, n_e = 0.2 i.e. one out of every five stars hosts a planet in a habitable zone where life can form.

Habitable Zone

The real estate within a solar system where life can form.

Temperature on the surface of a planet is dependent on two factors: (1) distance from the star; (2) luminosity of the star

Dyson’s Spheres

The second law of thermodynamics states that whenever energy is harvested, there is some wastage. The energy collectors have to heat up as they catch and store sunlight, making them glow in the infrared part of the spectrum. Dyson’s calculation showed that the infrared glow from such a starlight collecting megastructure could e seen across interstellar or even intergalactic distances.

What astronomers mean by Dyson’s sphere? Think of a vast pingpong ball the size of the Earth’s orbit, surrounding and entirely enclosing the Sun. The inside of the sphere is covered by solar panels or some light collecting technology.

To construct a shell one mile thick circumference the size of Earth’s orbit, we would need to grind up all the mass held in all planets in the solar system.

Kardashev Scale

Type 1: Civilization must harvest their planet’s entire budget of energy. For example, Earth gets almost a few thousand atomic bomb’s worth of energy per second from the Sun.

Type 2: Capture the entire output of the home star. Type 2 can harvest billions of times more energy than Type 1, like Dyson’s sphere.

Type 3: Harvesting all the energy produced by all the stars in an entire galaxy, like Dyson’s sphere across all stars in the galaxy.

Earth is currently Type 0.7 civilization.

Travelling Interstellar Distances

  • Generational ships
  • Cryosleep
  • Light sails
  • Wormholes
  • Warp drives (aka Hyperdrives)
  • Quantum Mechanics

Abiogenesis: the study of life’s origin, the creation of life from non-life.

The information required to guide all protein building is stored in deoxyribonucleic acid (DNA).

How are oceans formed?

The whole process of planet formation takes ten to hundred million years and a lot of heat gets generated. The water present is soon vaporized once the planet is formed. Whatever water is present in a mature world must be delivered after they form via comets and asteroids.

Biotechnical probability — probability of a technological civilization forming — if this is close to 1, then pretty much every habitable zone planet will form life that goes on to make a technological civilization.

Atmospheric characterization

Exoplanets are found by look at the fading star’s brightness when the line joining the Earth, the planet and the star are in one line, i.e. an eclipse is formed.

Similarly, when past through the atmosphere of the exoplanet, different wavelengths of light are absorbed and looking at these wavelengths it is possible to predict what elements occur on those planets.

Hence, we if can find the chemical composition of the planet, we can find evidence for life. We have found what we call a biosignature.

From biosignatures to technosignatures

“Sphere of thought” — the collective impact of all human rational planning and technological development — noosphere, aka technosignature.

If biosignatures are key to finding dumb life, then technosignatures are key to finding smart life.

Example: radio waves, pollution (CFCs), artificial lightning sources, solar collectors.

Terraforming Steps

  • Find some comets and redirect their orbits so they crash onto the planet. Comets are full of things like carbon dioxide and water.
  • You can get some of what you need from the frozen reserves on the planet itself. They are called volatiles and are things like nitrogen, carbon dioxide, ammonia, methane, which become gas at relatively low temperature.

Terraforming would also become a technosignature — finding a string of identical planets orbiting a distant star would indicate terraforming.

What makes Carbon unique?

  • Ability to form stable (strong and flexible) bonds with key elements like oxygen, nitrogen, sulfur and itself.
  • Even silicon is not as friendly as carbon. It’s bigger and heavier making less stable bonds.

Convergent evolution

  • Physical world imposes constraints on life that will lead to it finding the same solutions to the same problems whenever the problem arises.
  • Experiments show that accidents matter more and hence, we can say that —
    • It might be possible that we are indeed the only humans in the universe. On no other world would we expect all the zillions of accidents from microbes to large multicellular organisms to play out the same way.

Tell me everything there is to know about some star and I can tell you what its entire future would look like. A star would never surprise me, because its behavior is set by laws of physics. Life is certainly governed by laws of physics, but there’s more. Life is a complex system where laws of biology (i.e. evolution) also apply. That means life surprises. Life invents. Life goes beyond itself.