Davros

A simple way to look at the expansion is to drop down one dimensional level. (saw this metaphoric example in New Scientist many months ago) .... Imagine a 2D world on the surface of a 3D balloon. A spider sits on the surface. Expansion takes the form of the balloon enlarging .... resulting in all 'space' on the surface moving away from each other at the same time (but the spider not pulled apart - as in our 3D universe, we and the galaxy have enough gravity to 'fight' expansion for the time being).

There are practical applications of S/GR .... A major one being the operation of certain flavours of GPS systems and the interaction between Earth orbiting clocks and Earth surface based clocks. A. Clocks on Earth run slow, compared to high geo.sync orbiting satelite, by some 45 microseconds due to GR (ie earth clock closer to the centre of the nearest large gravitational mass (centre of the Earth). B. Clocks in high geo-orbit run slow, compared to earth surface clocks, by some 5 microsends due to SR (ie the geo-sync-sat is moving fast relative to the 0 speed surface clock). C. Combining the two "slow downs" it is clear that the geo-sync-sat clock appears to run some 40 ms fast, equating to an accumulating GPS inaccuracy of some 5 miles per day. Without knowledge of relativity (space/time) GPS would prove worthless within an hour, or a month, or a year (depending upon application). There are other applications too, but GPS is interesting since it applies both GR and SR effects.

Hey, this would not be pointless at all, in fact an artificial way to travel faster than light! If someone were to travel at 95% speed of light towards a planet 10 light years away, time dilation means that the traveller ages less than 10 years instead of more than 10 years during the travel ... this is clearly not pointless. During the above +/- 10 years time would have been constant in all respects, simply the traveller aged less and maybe convinced he traveled faster than light (when in fact he did not really do so).

Well I would actually think it is wrong to think of 'expansion' in a local area (eg within an atom or the solar system or even a galaxy). There is a constant effect, rather than a constant expansion. So if an object, or group of objects, is being held together by strong/weak forces or even weaker gravity, the expansion of space 'effect' merely reduces the effect of the above forces by an insignificant amount (maybe the orbit of pluto is a fraction of a mm further from the sun than might otherwise be the case. The expansion 'effect' is constant, not increasing, within the the same locale. It only increases over distance. (p.s. disclaimer: I do not have any formal science education, the above is my interpretation of my own reading).

expansion effects would be negligible for a galaxy compared to its own gravity.

thanks Janus, that was the answer I was looking for. thanks for the formulae yourdadonapogos.

The start of the original post of this thread: "If the fabric of space is expanding then the distances between galaxies is expanding, but this must also mean that the galaxies themselves are expanding." Not correct. Imagine blowing up a balloon that has two spiders (galaxies) sitting on the surface. As the balloon enlarges the distance between the spiders grows but the spiders themselves do not change size.

I am not a scientist but have a general interest in relativity. I am annoyed by the ever growing need to introduce exotic matter and additional dimensions into theories to account for effects in our universe. I have what maybe a completely silly idea (but would really like that to be confirmed! ) that may have a germ of interest .... 1. Suppose that the maximum velocity posssible in our universe was 0.0000005% higher than c. Call this c++. 2. light still has a measurable velocity c. But c is less than c++. Possibly from this a photon has mass. 3. If a photon has mass, why have we not detected it? Maybe because it is so so minimal. So minimal that even when traveling at 99.9999995% of c++ when it had maybe 10,000 times the mass of a photon at rest, it is still a minimal and undetectable mass (todate). 4. What would be the consequencies of a photon having minimal mass, rather than zero mass? A. Possibly this is the allusive Dark Matter? B. photons colliding with anything (planets/eyeballs) inflict a force. (However, assuming we receive countless photons from all directions all the time. these forces cancel out). C. Several formula to deal with singularities and expansion would be 'slightly' out and annoying ambiguities accounted for? (eg possible variance in value of c over time, possible variance of gravitational effects over distance) Anyhow, my question is, is this idea a dead duck non-starter? or could it possibly be just very unlikely?