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Yr 13 Physics 12 - Space > The Age of the Universe > Flashcards

The Age of the Universe Flashcards

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1
Q

what is red shift

A

the shift in wavelength of a stars spectrum

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2
Q

what causes red shift

A

the increasing separation between a star and earth

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3
Q

what is the name given to the effect of light red shifting due to the increasing separation between a star and earth

A

the doppler effect

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4
Q

what causes the doppler effect in general

A
  • when an observer receiving waves emitted from a moving body observes that the wavelength of the waves has been altered
  • as a consequence of the objects motion
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5
Q

if the siren on a stationary car was on and you were standing sill, what would you hear and why

A
  • the siren having a constant pitch
  • because the sound waves are travelling in all directions
  • but the car being still means that the wavelengths of them are constant around the whole car
  • therefore making the frequency of them constant
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6
Q

if the siren on a moving car was on and the car was driving past you, what would you hear

A
  • the pitch of the siren would increase as the car approached you
  • then when it passed you the pitch would decrease
  • the increased pitches would be above that than if the car was stationary
  • and the decreases pitches would be below that than if the car was stationary
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7
Q

why does the pitch increase as the car comes towards you

A
  • the car is driving in the same direction to the sound waves that are approaching you
  • this causes the distance between the sound waves to decrease as the wavefronts are compressed
  • this decrease in wavelength results in an increase in frequency (v = fY)
  • resulting in a higher pitch
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8
Q

why does the pitch decrease as the car drives away from you

A
  • the car is driving in the opposite direction to the sound waves that are approaching you
  • this causes the distance between the sound waves to increase as the wavefronts are stretched
  • this increase in wavelengths results in a decrease in frequency (v = fY)
  • resulting in a lower pitch
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9
Q

what is the motion of the car and the change in the sirens pitch an example of

A

the doppler effect

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10
Q

how would the EM spectra of a receding star compare to its its non receding counterpart

A
  • the spectral lines for the receding star would have shifted towards the red end of the spectrum
  • telling us that the wavelength of light is longer than it would be if it wasnt travelling away from us
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11
Q

how would the spectral lines of an approaching star compare

A
  • its spectral lines would shift towards the blue end of the spectrum
  • because its wavelengths of light would have decreased due to the doppler effect
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12
Q

what is this shift towards the shorter wavelengths of light called

A

blue shift / anti-red shift

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13
Q

how would the EM spectra of a star closer to us and a star further away from us both receding at the same speed compare (doesnt actually happen but for understanding’s sake)

A
  • they would essentially have the same amount of red shift in their line spectra
  • because the distance isnt what determines the intensity of the doppler effect
  • but the speed at which the object is moving towards or away from the observer
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14
Q

therefore, what does the amount of red shift a galaxy exhibits allow us to calculate about it

A

the speed at which it is moving

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15
Q

what equation allows to calculate this speed

A

z = (delta Y / Y) = (delta f / f) = (v / c)

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16
Q

what do each of those variables stand for

A
  • z = red shift ratio
  • Y = lambda (m)
  • f = frequency (Hz)
  • v = velocity of star / galaxy
  • c = speed of light (3x10^8)
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17
Q

in a lab sample the hydrogen alpha spectral absorption line has wavelength 656.285nm. in the spectrum for a nearby star this line is absorbed at a wavelength of 656.315nm. is this star moving towards or away from us and why

A
  • it is moving away from us
  • because there has been an increase in its wavelength detected from the star (656.315 - 656.285 = +0.03nm)
  • an increase in wavelength means red shift has occurred
18
Q

how would you calculate how fast the star is moving away from us

A
  • we have the wavelengths and the change in wavelength
  • so use z = (delta Y / Y) = (v / c)
  • delta Y = 0.03nm and Y = 656.285nm (the normal wavelength)
  • so 0.03 / 656.285 = v / 3x10^8
  • rearrange for v = (0.03 * (3x10^8)) / 656.285
  • v = 13700 ms-1
19
Q

why dont you need to convert the wavelengths into metres

A

because you are calculating ratios so it doesnt matter

20
Q

what is the practical relationship between a galaxys red shift and the distance it is away from us

A
  • they are directly proportional

- an increase in one means implies an increase in the other

21
Q

why is this relationship proportional if there is no direct link between the distance a galaxy is from us and its red shift

A
  • because the further away a galaxy is
  • the faster that galaxy is moving
  • and therefore the more red shift there is
22
Q

why does an increase in distance mean the galaxy is moving further away at a quicker speed

A
  • this is due to the expansion of the universe
  • so for a certain amount of time, a galaxy closer to us wouldve had less space ‘created’ between it and us than a further away galaxy would have had
23
Q

what is the typical model used to explain this phenomenon

A
  • a balloon with dots on it

- when blown up, the increase in the distance between two far away dots would be larger than two closer dots

24
Q

how did hubble come to the conclusion that the universe was expanding using different galaxies line spectra

A
  • he discovered that basically all galaxies showed red shift in their spectra
  • meaning that all galaxies were moving away from us (and each other)
  • therefore the universe had to be expanding
25
Q

what is hubbles law

A

v = H(0) * d

26
Q

what do each of those variables mean

A
  • v = velocity of recession
  • H(0) = hubbles constant
  • d = distance between body and earth (in Mpc)
27
Q

what is the value of hubbles constant

A

H(0) = 70.9 kms-1Mpc-1 or 70,900 ms-1…

28
Q

a supernova appears in the sky and astronomers find that it has a red shift of z = 0.45. what is the speed of the supernova

A
  • z = v / c
  • v = z c
  • v = 0.45 x (3x10^8) = 1.35x10^8 ms-1
29
Q

how far away is the supernova

A
  • v = 1.35x10^5 kms-1 for similar units
  • using v = H(0) d, d = v / H
  • (1.35x10^5) / 70.9 = 1900Mpc
  • d = 1900 Mpc
30
Q

regarding z, how do you know if your shift is red or blue and why

A
  • red shift = +ve delta Y
  • blue shift = -ve delta Y
  • because change in wavelength is calculated by subtracting the new value by the old one
  • so red shift which has a new value bigger than the old one gives a +ve value
31
Q

what does pc stand for again

A

parsec

32
Q

what is the distance one 1 pc

A

3.09x10^16 m

33
Q

therefore what is the distance of 1 Mpc

A
  • mega = 1x10^6

- so (3.09x10^16) x (1x10^6) = (3.09x10^22 m)

34
Q

given d = 1900 Mpc, what is that distance in meters

A

1900 x (3.09x10^22) = 5.871x10^25 m

35
Q

why is finding more accurate values of the hubble constant so important

A
  • because it will tell us how quickly the universe is expanding
  • from this we can accurately work out how long ago the big bang was
  • and when (if it will) our universe dies
36
Q

for an object to travel a distance d(0) from the beginning of time, at a speed pf v(0), the time T(0) could be calculated using what basic equation

A

time = distance / speed

37
Q

given T(0) = d(0) / v(0), what relationship does the hubble constant and time have

A
  • as v = H(0) * d, H(0) = v(0) / d(0)
  • given T(0) = d(0) / v(0)
  • T(0) = 1 / H(0)
38
Q

how was this equation used to calculate the age of the universe

A
  • we know H(0) = 70.9 kms-1 Mpc-1 = 70,900 ms-1 Mpc-1
  • and 1 Mpc = 3.09x10^22 m
  • therefore 70,900 / 3.09x10^22 = 2.29x10^-18 ms-1 m-1
  • the m and m-1 cancel out
  • giving H(0) = 2.29x10-18 s-1
  • using T(0) = 1 / H(0), diving 1 by 2.29x10-18 s-1 (where 1/1 divided by 1/s = 1/1 *s/1 = s) gives us the unit we want
  • 1 / 2.29x10-18 s-1 = 4.36x10^17s
  • which tells us the universe is roughly 13.8 billion years old
39
Q

how do you get the step where you divide 70,900 by 1 Mpc, surely you should be multiplying to cancel out the Mpc-1 in the units right?

A
  • 70900 ms-1 Mpc-1 is the same as 70900 (m / s Mpc)
  • therefore inputting the value of 1 Mpc (as the unit equates to ‘per’ Mpc) into the units gives you a division
  • this replaces the Mpc-1 unit with the m-1 unit
40
Q

what is the big bang

A
  • the theory that he universe expanded outwards

- from a single point to the currently observed situation

Yr 13 Physics 12 - Space (6 decks)

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