The Fate of the Universe

Question 1

why has there been variations in the values of the hubble constant

Answer 1

because of the different observational methods used to find it

Question 2

why is having an inaccurate hubble constant value problematic

Answer 2

• it gives a huge variation in possible ages of the universe

- ranging from 10 to 20 billion years

Question 3

given that the hubble constant is used to calculate the age of the universe, will we ever truly know the age of the universe and why

Answer 3

• no
• because the hubble constant is measured using experimental methods and instruments
• which have their own uncertainties
• so we can only get more accurate answers

Question 4

what is the universe constantly doing

Answer 4

expanding

Question 5

will the universe continue to expand forever

Answer 5

we dont know

Question 6

what factors determine what route the universe will take over the many years

Answer 6

• the mass of the universe

- the density of the matter within the universe

Question 7

what force naturally opposes the expansion of the universe given that there is matter within the universe

Answer 7

gravity

Question 8

what is the big crunch

Answer 8

• a possible theory for the future of the universe
• where gravity overcomes the expansion of the universe
• causing it to contract back inwards into a singular point

Question 9

what condition needs to be met in order for the expansion of the universe to forever continue

Answer 9

• the matter in the universe has to be sparse

- specifically below a critical density

Question 10

why does this condition need to be met

Answer 10

• the force of gravity between particles decreases as the distance between them increases
• if matter in the universe is sparse the gravitational forces between matter will be generally weak
• meaning gravity wont ever be able to overcome the expansion of the universe
• so it will continue forever

Question 11

therefore what condition needs to be met for the big crunch

Answer 11

the matter in the universe has exceeded the critical density

Question 12

what is a flat universe

Answer 12

• a universe which reaches a size where its expansion and gravity are balanced
• so its size doesnt change after it reaches its maximum size

Question 13

what is a closed universe

Answer 13

• a universe which reaches its maximum size
• then will begin to contract due to gravity
• the big crunch scenario basically

Question 14

what is an open universe

Answer 14

• a universe which continues expanding forever

- the ‘below critical density’ scenario

Question 15

what would a graph of size over time look like for a flat, closed and open universe

Answer 15

• the flat line would look like an logx graph (+ve gradient but naturally plateaus)
• the closed line would look like a -x^2 graph (molehill)
• the open line would be a straight line with a +ve gradient

Question 16

when trying to work out the density of the universe, what did vera rubin discover about the stars in Andromeda

Answer 16

• the stars in the galaxies tend to rotate at similar speeds

- whatever their distance from the centre of the galaxy

Question 17

why was this a peculiar find

Answer 17

• because the stars closest to the centre shouldve been rotating at quicker speeds
• similar to our solar system where the planets further away from the sun rotate slower

Question 18

what can we estimate from working out the luminosity of a galaxy

Answer 18

the mass of all its stars

Question 19

what force should all the stars in a galaxy be feeling if the galaxy is rotating

Answer 19

a centripetal force towards the centre of the galaxy

Question 20

what problem did scientists come across when measuring the rotational speed of the stars in the galaxy and their relationship to their mass suggested by the luminosity calculations

Answer 20

• that their mass was not enough to create the centripetal force needed to keep the galaxy spinning
• in other words, the gravitational centripetal force shouldnt have been enough to hold the stars in place against their rotational velocity

Question 21

what was the only conclusion the scientists had to make because of this

Answer 21

that galaxies contain a lot of mass that does not emit light

Question 22

what is this mystery mass called

Answer 22

dark matter

Question 23

what percentage of mass was actually detectable in the galaxies of that that shouldve actually been there

Answer 23

about 10%

Question 24

what two possible candidates did we have for dark matter

Answer 24

• black holes

- interstellar gases

Question 25

yet what is the problem with these two suggestions

Answer 25

- they are also not observed in sufficient quantities | - so even if they did contribute, there would still be more mystery matter present

Question 26

what does einsteins theory of gravity simply state

Answer 26

- that large masses will deform space-time (the fabric of the universe) - so that it accelerates things

Question 27

how has his theory been supported by photos of deep space

Answer 27

- we have observed light bending around large masses - like black holes or galaxies - rather than passing through them like a lens - suggesting space-time itself was curved

Question 28

what did the hubble space telescope discover about the expansion of the universe

Answer 28

- it is not slowing down | - but it is actually accelerating

Question 29

where is this energy powering the accelerating expansion of the universe, which seems to defy its own gravity, coming from

Answer 29

we dont know

Question 30

what is the name given to this mystery energy

Answer 30

dark energy

Question 31

what are the percentages of ordinary matter, dark matter and dark energy that compose the universe

Answer 31

- ordinary matter = 5% - dark matter = 27% - dark energy = 68%