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It depends what you mean by nearest galaxy, but the conversion factor between light years and AU is about #63000#


Let's work out a conversion factor between light years and AU first.

The Sun is roughly #93000000# miles from the Earth and light travels at about #186000# miles per second.

So #1# AU is about #500# light seconds.

There are #86400# seconds in a day and about #365.25# days per year, hence:

#86400 * 365.25 = 31557600" "# seconds per year.

Dividing this by #500# we arrive at:

#31557600/500 = 63115.2 ~~ 63000" "# AU per light year.

How far away is the nearest galaxy from the Milky Way?

The very nearest galaxy would be one of the small satellite galaxies.

There are about #50# galaxies within about #1.4# million light years of the Milky Way. The closest are about #1000# light years from the edge, which by our reckoning would be about #63000000 = 6.3 xx 10^7# AU from the edge.

Perhaps of more interest is the distance to the Andromeda galaxy, our largest neighbour in the Local Group. This is about #2.5# million light years away, which would make it about #160# billion AU away.


It depends...


There are some small satellite galaxies of the Milky Way galaxy, but let's consider our largest neighbour in the Local Group, namely the Andromeda Galaxy.

This is situated approximately #2.5# million light years away.

That means that from the perspective of the people who stay at home, a round trip would take at least #5# million years.

Note however, that the traveller(s) could experience significantly less time, if they travel with sufficient speed.

For example, if they used a spacecraft that accelerated constantly with an acceleration of #1#g (i.e. #9.8 ms^(-2)#) for about #14# years (ship time), then decelerated at #1#g for about #14# years, that would be sufficient to travel from our galaxy to the Andromeda Galaxy.

Returning home the same way, the traveller(s) would experience another #28# years of time, but arrive home to find that #5# million years had passed.


Please read below.


We have, however many hypotheses that could explain it, such as string theory or m-theory, the problem we have right now is that all the predictions these ideas make about the universe are impossible to test with our current technology. You see, all scientific models make predictions and we can prove or disprove them by going out and making observations that confirm or deny that model.

  • What was there before it?

Same as above, we have models that could explain it, but the observations are beyond our tech so far.

  • What is some evidence for it?

In the 1920s Edwin Hubble (the telescope was named after him) discovered that all galaxies are flying away from us, and the further away a galaxy is from us the faster it is going away from us. This proved the Universe was expanding. Meaning it must have been smaller early on. This begat the Big Bang Theory.
There are many cosmological observations that corroborate this, and one of the best, which was predicted by the theory itself, is the Cosmic Microwave Background.

  • Why do some people not agree?

Overall the school system has done a poor job of communicating the science to the people. The media also doesn't help as it is sensationalist and misrepresents the issues most of the time, leading to people distrusting science. Religion also plays a part in it as science disproves some of the stuff written in their holy books, so they (true to their doctrines) truest blind faith over knowledge.


It is nothing to do with the rate of expansion of the universe, but it is perfectly possible to travel forward in time.


It is nothing to do with the rate of expansion of the universe and everything to do with the speed of light.

We are travelling forward in time all of the time, but the time experienced is relative to your frame of reference. As a result, it is possible (in fact unavoidable) that we experience different lengths of time according to how we move around.

Most of the time, this time dilation is too small to be easily measurable, but there are some scenarios in which it is much more noticable.

For example, we detect far more muons at the Earth's surface coming from cosmic rays than we would expect. Muons have a half life of about #1.56# microseconds, but travel at about #0.9 c#. As a result, they appear to have a half life about #5# times as long from the perspective of a ground observer. We can explain this in terms of time dilation by a factor of #5#. From the muon's perspective they have a perfectly normal half life, but they experience length contraction by about a factor of #5#.

If we had a spaceship that could sustain a #1g# (#9.8ms^(-2)#) acceleration or deceleration for extended periods, then it would be possible for a traveller to make the journey to the Andromedra galaxy (#2.5# million light years away) and back in about #56# years - ship time. When they returned they would find that #5# million years had passed.


The strong force holds atomic nuclei together and the weak force causes radioactive decay.


The strong nuclear force is responsible for binding protons and neutrons together in an atomic nucleus. It is strong and short ranged and has to overcome the electromagnetic force which is pushing positively charged protons apart.

A good example of the strong force is the fusion process which happens in smaller stars such as our sun. Positively charge protons repel each other. At the extreme temperatures and pressures in the sun's core, two protons can get close enough together for the strong nuclear force to bind them into a bi-proton or Helium-2 nucleus.

A bi-proton is very unstable and most of them fly apart. For the fusion process to continue to produce Deuterium the weak nuclear force is required.

The weak nuclear force is responsible for radioactive decay by being able to convert a proton into a neutron of vice versa. To be more precise it converts an up quark to a down quark or vice versa by means of the W boson. In the case of fusion a proton is converted into a neutron, a positron and an electron neutrino.

#W^+ ->e^++nu_e#

In fact the strong nuclear force doesn't really exist. Early theories described the strong nuclear force as binding protons and neutrons using the pion as the force transmitting boson. We now now that protons, neutrons and pions are composite particles consisting of quarks bound by the colour force transmitted by gluons. So, the strong force is actually a residual effect of the colour force extending beyond the inside of protons and neutrons to bind them together.


The four fundamental forces will be linked by a Theory of Everything (TOE).


Electromagnetism the the force which describes the interactions between charged particle. It is mediated by the photon.

Electricity and magnetism were originally thought to be separate forces until they were unified. Maxwell's equations describe electricity and magnetism.

Quantum Electrodynamics (QED) completed the picture by describing how electrons move in atoms.

The weak nuclear force is responsible for radioactivity and aspects of nuclear fission and fusion. It is propagated by the W and Z bosons. Typical weak interactions convert a proton into a neutron, a positron and an electron neutrino or a neutron into a proton, an electron and an electron anti-neutrino.

#p -> n + W^+# then #W^+ -> e^+ + nu_e#
#n -> p + W^-# then #W^(-) -> e^(-) + bar nu_e#

The electromagnetic force and the weak nuclear force were unified by the electro-weak theory.

The strong nuclear force is not really a force. The colour force also known as Quantum Chromodynamics (QCD) describes how quarks are bound together in protons, neutrons, mesons and other baryons. It is propagated by the gluon. The strong force is a residual effect of QCD operating at distance greater than the size of protons and neutrons.

Attempts are being made to create a Grand Unified Theory (GUT). Which unifies the electro-weak theory with QCD. A GUT is going to take some time to produce and verify.

This leaves gravity which actually isn't a force. It is the result of curved space time as described by Einstein's General Relativity.

A Theory of Everything (TOE) is required to unify a GUT and gravity. This is a long term goal.

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