The observable examined

End of days

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Lecturer: Dr. Rita Wechsler

A very entertaining lecture. Wechsler likes to deal with very large time scales (on the order of billions of years) and it was exteremely interesting and fun. I liked the way she kept referring to “stuff” when dealing with dark energy/dark matter.So here goes…..

  • Till about a 100 years ago, the prevailing view in Cosmology was that the universe was static
  • In fact, Einstein added a term in his theory of general relativity (which naturally allowed for expansion and contraction) to make it static!
  • Galaxies, I think, are also known as spiral nebulae
  • Hubble used spectrum to measure velocities
  • V= Hod (velocity is proportional to distance – H0 is the Hubble constant)
  • More matter in the universe implies expansion is slower. If we measure expansion rate, the age of the universe can be calculated
  • Our universe is 13.7 Billion years old !!
  • Big Bang
    • Universe is expanding
    • past universe much denser
    • denser means hotter in the past
    • implies our universe is now cooling and diluting over time

Time scale cheat sheet

  • Age of the universe : 13.7 Billion years
  • 1st Galaxies              : 13.3 B
  • Milk Way                  : ~12-13B
  • Sun                            :  4.6B
  • Earth                         : 4.5B
  • Life on Earth            : 3.8B
  • Mammals                  : 200 Million years
  • Humans                     : ~ 400K

Lets stop here for a moment (actually a sec) and put this perspective.  If the Universe were 1 sec old, our existence on this Earth as a species has lasted a mere 30 microseconds. If you and I were to live the full 100 yrs, it is a mere 7 nano seconds since the dawn of Time. Again, 7 nanoseconds!!

I think somebody asked, “where is the center of our universe?” . Wechsler answer was, Big Bang happened at a single point. We are at the center of our observable universe (limited by the distance light has travelled).

There was a fun section on how life on earth may end. Here are some interesting tidbits

  • Chances of the earth being destroyed by an Asteroid are 1 in 700000 over a lifetime. In fact, Congress has mandated that all asteroids upto 140 meters (?) in diameter be catalogued and monitored
  • Gamma ray bursts – would completely fry the ozone. Burst within 10000 light years would be dangerous. But the odds are only 1 in 14Million over a lifetime. So no real worries there!
  • Dusty Milky Way – could block our sun. Imagine what could happen. Chances – 1 in 30Million years. Rest easy.
  • Death of our Sun – He is middle aged now. Burning hydrogen and getting hotter. Also getting brighter by 10% every Billion years. In 6 Billion years our Sun will be dead. Long live the Sun!

The Milky Way has the brightness of 30 Billion suns !! What kind of sunglasses would you need if you lost your way and ended up near the Milky way?!

In about 3 Billion years, the Milky Way will collide with Andromeda. We watched an exhilarating video simulation of this event . Upshot is that the collision will completely upend the spiraling Milky Way, which means we are also in trouble.

The expansion of the Universe is accelerating. This is contrary to most expectations.

Distinct from dark matter there is this stuff nobody really understands called Dark Energy.

Interestingly, the make up of the universe is

  • 4% atoms (0.4% stars, 3.6% gas)
  • 26% dark matter
  • 70% dark energy

95% is not in the periodic table or in the standard model !!


Written by asterix98

November 24, 2010 at 6:52 am

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