The Fate of the Universe Flashcards
why has there been variations in the values of the hubble constant
because of the different observational methods used to find it
why is having an inaccurate hubble constant value problematic
- it gives a huge variation in possible ages of the universe
- ranging from 10 to 20 billion years
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
- 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
what is the universe constantly doing
expanding
will the universe continue to expand forever
we dont know
what factors determine what route the universe will take over the many years
- the mass of the universe
- the density of the matter within the universe
what force naturally opposes the expansion of the universe given that there is matter within the universe
gravity
what is the big crunch
- 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
what condition needs to be met in order for the expansion of the universe to forever continue
- the matter in the universe has to be sparse
- specifically below a critical density
why does this condition need to be met
- 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
therefore what condition needs to be met for the big crunch
the matter in the universe has exceeded the critical density
what is a flat universe
- a universe which reaches a size where its expansion and gravity are balanced
- so its size doesnt change after it reaches its maximum size
what is a closed universe
- a universe which reaches its maximum size
- then will begin to contract due to gravity
- the big crunch scenario basically
what is an open universe
- a universe which continues expanding forever
- the ‘below critical density’ scenario
what would a graph of size over time look like for a flat, closed and open universe
- 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
when trying to work out the density of the universe, what did vera rubin discover about the stars in Andromeda
- the stars in the galaxies tend to rotate at similar speeds
- whatever their distance from the centre of the galaxy
why was this a peculiar find
- 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
what can we estimate from working out the luminosity of a galaxy
the mass of all its stars
what force should all the stars in a galaxy be feeling if the galaxy is rotating
a centripetal force towards the centre of the galaxy
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
- 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
what was the only conclusion the scientists had to make because of this
that galaxies contain a lot of mass that does not emit light
what is this mystery mass called
dark matter
what percentage of mass was actually detectable in the galaxies of that that shouldve actually been there
about 10%
what two possible candidates did we have for dark matter
- black holes
- interstellar gases
yet what is the problem with these two suggestions
- they are also not observed in sufficient quantities
- so even if they did contribute, there would still be more mystery matter present
what does einsteins theory of gravity simply state
- that large masses will deform space-time (the fabric of the universe)
- so that it accelerates things
how has his theory been supported by photos of deep space
- 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
what did the hubble space telescope discover about the expansion of the universe
- it is not slowing down
- but it is actually accelerating
where is this energy powering the accelerating expansion of the universe, which seems to defy its own gravity, coming from
we dont know
what is the name given to this mystery energy
dark energy
what are the percentages of ordinary matter, dark matter and dark energy that compose the universe
- ordinary matter = 5%
- dark matter = 27%
- dark energy = 68%
