Differences and similarities between electric fields and gravitational fields
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Electric fields are both attractive and repulsive while gravitational fields are always attractive
Electric fields are stronger than gravitational fields
However they are both radial from a point
Flat universe
When the universe expands to a constant size
Closed universe
The universe will stop expanding at some point and then collapse again
Open universe
Universe could continue expanding forever
Scientists can’t calculate the density of the universe
We can measure the mass of all the stars in the galaxy from its luminosity
Galaxies rotate which means that all the stars they contain must be experiencing a centripetal force towards the Centre of the galaxy’s rotation.
When the rotational speed is measured, the mass suggested by the luminosity calculations is not nearly enough to create the centripetal force needed to keep the Galaxy spinning
This suggests that the galaxies must contain a lot of mass that does not emit light
No one knows what the dark matter could be
