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Flashcards in D.3 Cosmology Deck (22):

What is red shifted light?

Light from distant galaxies is received on Earth at a wavelength that is longer than that emitted.


How does the doppler effect explain red shifted light?

The galaxies are moving as from us so the universe is expanding.


What does the universe expanding suggest about the previous universe?

That it was once smaller and had a beginning, The Big Bang which marks the beginning of time and space and the creation of all energy and matter. It happened everywhere in the universe which was then a point. At the early sages of the life of the universe the temperature would have been very high as the universe expanded it called down.


What is Einstein's interpretation of the red shift?

Space expands giving the illusion of galaxies moving away from one another. As space expands the wavelength of the photons emitted form distant galaxies also stretched by the time it gets to us, R is the scale factor of the universe, hence we measure a longer red shifted wavelength.


What is the equation for the red shift?

Z = lambda/lambda0

where lambda0 is the emitted wavelength and lambda is the received wavelength.


What does Hubble's law suggest?

Distant galaxies move away form each other with a speed that is proportional to their separation v = Hod Hubble's law only applies to distant galaxies.


What is the graph of Hubble's law?

The graph is a straight line passing through the origin, the axis are speed versus distance and the slope of the fray is Ho.


What is the present accepted value of the Hubble constant?

Ho = 68kms-1Mpc-1


How is the speed of a receding galaxy obtained?

Using the doppler formula
z = deltalambda/lamda0 = v/c

this can only be used or small red shift up yo about 0.2


How do you derive the equation for Hubble time?

v = d/T where T is the present age of the universe.
Thus d/T = Hod giving a value of T = 1/Ho which is about 14 billion years.


Why is Hubble time an overestimate of the age of the universe?

The expansion speed was greater at the beginning, so hubble time is only an upper bound on the age of the universe.


What is the cosmic scale factor?

As the universe expands the physical distance between any two point increase, the scale factor R is used to quantify this. This factor varies with time.


What is the ratio of the physical distance d between the two points given and their separation d0 in the past?

d/d0 = R/R0 where R is the scale factor now and R0 is the scale factor in the past.


What is the actual value of the scale factor an indication of?

The size of the universe.


How do we deduce the formula for the scale factor?

From z = delta lambda/lambda0 we deduce that z = (lambda - lambda 0)/ lambda 0 which equals (lambda/lambda 0) - 1 which in turns equals R/R0 -1


What is cosmic microwave background radiation?

The best evidence for the big bang theory - it is black body radiation coming from all directions in the microwave region. It is the remnant of the radiation that filled the universe in its early stages when the temperature was very high. This means that in the past the peak wavelength was smaller and the temperature was very high, this is strong evidence for a hot big bang. As space stretched the initial wavelength also stretched to its present value.


How is the temperature of the universe 3K and the peak wavelength 1.07 mm shown by an equation?

lambda0 x T = 2.9 x 10-3mK
T = 2.9 x 10-3/1.07mm
T = 2.7 K


What was the evidence for the universe accelerating in its expansion?

Type Ia supernovae.


What is a Type Ia supernova?

Occurs when a white dwarf that is part of a binary star system collected mass from its companion star thus increasing its own mass. Once the Chandrasekhar limit of 1.4 solar masses is exceeded the white dwarf explodes because of runaway nuclei fusion reactions that release large amounts of energy increasing its luminosity massively become a type Ia supernova.


how does the luminosity vary for this type of supernova?

It peaks and drops off, they all have the same value of peak luminosity.


How can we calculate the supernovas distance from earth?

We can observe the maximum apparent brightness b of such a supernova from
b = L/(4PiD^2) so we can directly calculate its distance form Earth. From its Doppler shift we can also determine the sped at which it is moving away.


How does the supernova provide evidence for the universe accelerating?

They were dimmer than expected based on the big bang model, could be explained by assuming that they were actually further away so the universe is accelerating.