Relativity and the Universe

Chapter 30

Page 724

The Big Bang

• The universe began with a gigantic explosion about 10-20 by ago

• Hubble found the first compelling evidence

• Galaxies are moving away from each other

• Demo: balloon

How did we come up with this?

Doppler Shift

• A shift in wavelength because of motion of source or observer

• Happens with – Sound– Light

• Waves are– Scrunched together with approaching object– Spread out with receding object

We see a red shift

• What does this mean?

• Other galaxies-stars are moving away from us.

Bottom galactic star, a nearby galaxy,

a medium distance galaxy, distant galaxy

Read from bottom up

The Universe is Expanding

In class film link

Background Cosmic Radiation

• Faint microwave radiation-dying embers of the explosion discovered in 1964-65 by Arno A Penzias and Robert Wilson

• They were trying to get rid of microwave noise in their radio antenna

• This noise had been predicted by the Big Bang Theory

Einstein showed space and time are bound together

• When we look at the stars we are looking back in time

• We usually use three dimensions

• Time is the fourth

General Relativity

• Mass warps space

• So . . . What is its shape?

A baseball dropped onto the sheet will roll toward the bowling ball. Einstein theorized that smaller masses travel toward larger masses not because they are "attracted" by a mysterious force, but because the smaller objects travel through space that is warped by the larger object.

Geometry of space-time

• negatively curved or hyperbolic geometry sometimes called saddle-shaped

• Euclidean or flat geometry

• positively curved or spherical geometry

Matching

A. Saddle shaped

B. Spherical

C. Flat or Euclidean

Special Relativity

1. The speed of light is the same for all observers, no matter what their relative speeds.

2. The laws of physics are the same in any inertial (that is, non-accelerated) frame of reference.

http://scholar.uwinnipeg.ca/courses/38/4500.6-001/Cosmology/SpecialRelativity.htm

Time Dilation

• A clock in a moving frame will be seen to be running slow, or "dilated"

• The time will always be shortest as measured in its rest frame

Length Contraction

• In order to measure the length of an object moving relative to you it is necessary for you to get the two endpoints of the object measured at exactly the same time.

• The length of an object appears shorter to an observer who is moving relative to the object.

Twin Paradox

The twin paradox arises from the time dilation effect. Say there are twin brothers. One brother stays at home in a slow speed environment. The other brother goes away in an ultra-fast spaceship. The "slow" twin ages considerably (loses his hair). The younger twin returns still young (having all of his hair).

This situation is called the twin paradox.

Three Theories of the Future of the Universe

• Expansion-the universe will continue to expand

•

The Big Crunch-the universe will expand then fall in on itself

• If the gravitational attraction of all the matter within the observable horizon is high enough, it could slow the expansion of the universe, and then reverse it.

Oscillating Universe-

•

-the universe will expand then contract repeatedly• Big Bang-Big Crunch-Big Bang-Big Crunch

Dark Matter

• As much as 90% of the universe may be dark matter

• This is undetectable by current means

• Tiny ripples in the temperature of the cosmic background radiation hint that ordinary matter makes up only a small percentage of the universe

String Theory