Chapters 17,18: Cosmology and Life in the Universe Nearly every speck of light in the image is a galaxy

Chapters 17,18: Cosmology and Life in the Universe

Nearly every speck of light in the image is a galaxy.


A map of the distribution of galaxies seen out of the plane of the Milky Way


Is the universe infinite or closed. Olbers’s Paradox says in must be finite because if it was infinite then every direction one looked in space would ultimately land on the surface of a star and the whole sky would be as bright as the Sun’s surface.


Hubble’s Law states that

Recession velocity = Ho X distance

Where Ho is the Hubble constant

Since velocity is distance/time, if we assume the universe has been expanding since the Big Bang then we can invert the equation for Hubble’s law and calculate how long it has been since the Big Bang.

Time since Big Bang = 1/Ho gives 14 billion years


At a time 1/Ho the universe began in an event we call the Big Bang

But like living on the surface of a balloon, we can see no beginning.


Also, as the balloon expands we see all parts reseeding from allothers. This explains why we see all the other galaxies speeding away from us.


The expanding universe also caused the wavelengths of radiation from the Big Bang to be red shifted. We see this today as the microwave background radiation.


Classical thought says depending on how much matter there is in the universe we have three possible outcomes.

Modern evidence points to a fourth outcome, an accelerating expansion.


1) too little mass means we expand forever (death by ice)

2) too much mass and we get the big crunch (death by fire)

3) just the right amount and we eventually stop expanding (also death by ice)

4) But truth is an increasingly expanding Universe. How can this be?


Currently astronomers cannot find enough mass to close the Universe.

The increasingly expanding Universe suggests we have negative energy and/or anti-gravity. This is a very active area of research.


As the Big Bang occurred we went from a radiation dominated universe to a matter dominated universe


Hydrogen and Helium are the only two atoms made during the Big Bang. All other elements were manufactured in by the stars and supernovae explosions.

The ration of Helium to Hydrogen is an important constraint to current theories.

It is difficult to tell if spacetime is curved because the distances mw can measure are so small compared to the universe


Somehow dark mater caused the ordinary mater in the Universe to be clumpy.


Is there anybody out there?



While we can recreate amino acids under early Earth conditions, we have not been able to “create” Life.

Radio astronomers can detect complicated molecules in dark molecular clouds.

Miller-Urey experiment


Organic mater is found in meteorites.

And life is found to grow where we never thought it could exist.


Different star have different ranges of habitable zones


number of technological, intelligent civilizations now present in the Galaxy

rate of star formation, = averaged over the lifetime of the Galaxy

fraction of stars X having planetary systems

average number of habitable X planets within those planetary systems

fraction of those X habitable planets on which life arises

fraction of those X life-bearing planets on which intelligence evolves

fraction of those intelligent-life X planets that develop tech- biological society

average lifetime of a technologically X competent civilization.

Drake’s Equation


Many astronomers think the best place to look for ET is in the water hole part of the electromagnetic spectrum.

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Chapters 17,18: Cosmology and Life in the Universe Nearly every speck of light in the image is a galaxy