C20 Cosmology (The Big Bang) Flashcards
What does the Big Bang theory attempt to describe?
origins and development of early universe. All objects initially contained in a singularity, which suddenly expanded outwards. The universe not stopped expanding since then.
Evidence for the Big Bang Theory: (4)
-Hubble’s Law shows universe, expanding, through the red shift of light from distant galaxies.
-Also cosmic microwave background radiation. Scientists were first measuring radiation in space, and found a constant interference. There was no justification, except the Big Bang theory.
-Also the abundance of hydrogen and helium in our universe.
-Originally high energy gamma photons, but as universe expanded, wavelength of these photons, stretched into the microwave region – this provides a constant signal now.
-However no experimental evidence for this theory– we can’t recreate the initial conditions of the Big Bang.
The Evolution of the Universe: (12)
• The Big Bang: Time and space created; the universe is a dense, hot singularity.
• 10-35 s: Universe expands rapidly, in a period of incredible acceleration (known “inflation”). There is no matter, only high energy gamma photons and electromagnetic radiation.
• 10-6 s: First fundamental particles gain mass. The mechanism behind this is, not fully understood but it involves the Higgs Boson.
• 10-3 s: Most of the mass is created using pair production. The first hadrons come from quarks.
• 1s: Production of mass is halted.
• 100s: Protons and neutrons fuse to form deuterium, helium, lithium and beryllium nuclei, but nothing heavier. Rapid expansion continues. 25% of matter is helium nuclei.
• 380 thousand years: It is now cool enough for the first atoms to form.
• 30 million years: The first stars form, and fusion creates heavier elements.
• 200 million years: Our galaxy forms as gravitational forces pull together clouds of hydrogen and existing stars.
• 9 billion years: The solar system forms by a nebula from a supernova. Followed by the formation of our sun, and then the Earth almost 1 billion years later.
• 11 billion years: Primitive life begins on Earth.
• 13.7 billion years: The first modern humans evolve.
What is the Doppler effect used to determine?
-Used to determine speed of moving objects (motorist, tennis balls to rotating galaxies).
What is frequency the same as?
Frequency is the same as the pitch of the sound waves being emitted.
Define the Doppler Effect?
Whenever a wave source moves relative to an observer, the freq and wavelength of waves received by observer change compared with what would be observed without relative motion.
In the second, wave source is moving away from observer C, towards D, the waves received by D will be compressed (have shorter wavelength and so higher freq). For observer C, waves stretched out, wavelength becomes longer and lower freq is observed.
The faster the source moves, the shorter…
The wavelength at observer D are, and the longer the wavelengths at observer C become.
-This effect applies to all types of waves.
Light from stars can be analysed in many ways (one technique involves looking at absorption lines in the spectra from stars).
Doppler effect can determine what?
-Doppler effect can determine, relative velocity of a distant galaxy, and speed of rotation of stars and galaxies.
How can the Doppler Effect be used to determine the velocity of distant galaxies and speed of rotation of stars and galaxies?
First, absorption spectrum of specific element is determined in lab. The same spectrum is observed in light from distant galaxy, any difference between the observed wavelengths, caused by the relative motion between the galaxy and Earth.
If galaxy moving towards Earth, the absorption lines will be blue-shifted, they move towards blue end of spectrum, because wavelengths appears shorter.
If galaxy moving away, absorption lines will be red-shifted, they move towards the red end of spectrum, because wavelength appears stretched.
What does Red Shift prove?
An expanding Universe
How fast wave source moves relative to observer affects what?
the size of observed shift in wavelength and freq.
For electromagnetic waves, Doppler equation:
Change Lambda / Lambda = Change f / f = v / c
-Lambda, the source wavelength
-Triangle lambda, the change in wavelength recorded by observer
- f, the source freq
-Triangle f, the change in freq recorded by observer.
- v, the magnitude of the relative velocity between the source and observer
- c, speed light through vacuum
What’s a Binary System?
Binary system, where two stars orbit each other.
Doppler equation can only be used for…
galaxies with speed far less than speed light,
Equation shows faster the source moves, the greater the observed change in wavelength and freq. The wavelength of each absorption line changes by the same percentage for particular moving galaxy.
What does Hubble’s Law state?
Hubble’s law states that the recessional velocity (v) of a galaxy is proportional to its distance from Earth.
Means further away star from Earth, faster it is moving away from us.
