# Speed of civilisation development

1. Aug 20, 2008

### northcave

Newbie disclaimer :)

Ok you're probably going to roll you eyes at this one. "oh here is another newbie with a dumb 1st post". But anyway i'll continue anyway since i'm curious.

Please also note that although i am fasinated by physics etc i have very little knowledge of it so please feel free to correct me where necessary.

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Right OK.... Now we know that time slows down the faster we go up till the speed of light, right? I'm assuming this is directly proportional.

Anyhow, if we take our own galaxy as an example. I read somewhere than a study was made to estimate the probability and number of other advanced civilisations in our galaxy based on the estimated number of planets around the estimate number of stars (advanced being like ourselves or more advanced). The result was many to say the least. That aside lets assume there is plenty of planets which can sustain life.

Now.... if the solar systems which are closer to the centre of our galaxy, like in a whirl pool, are moving around the black hole (or whatever is in the centre) at a slower rate that the ones on the outside like ourselves, does that mean that we're experiencing a slightly slower time then them? In that case, over millions / billions of years wouldn't the probability of more advanced cizilisations be increased towards the centre of the galaxy simply because they've been moving at a slightly faster rate of time and hence a longer time to develop generally.

Have I totally lost the plot here or is that potentially correct?

2. Aug 20, 2008

### Chronos

Beings residing on a body experiencing time dilation would be riding the short bus. Residents of slow moving bodies would advance more rapidly from their perspective.

3. Aug 21, 2008

### Ich

Yes, "potentially correct". There is gravitational time dilation, too, so the stars in the hinterland would actually age more. But the effect is no more than a few thousand years.

4. Aug 21, 2008

### yuiop

Hi Northcave,

it is not directly proportional. The time dilation factor is $$\sqrt{1-v^2/c^2}$$ so for example when moving at 80% of the speed of light the time has only slowed down by 40%. It only gets really noticeable above 90% of the speed of light.

Generally in an orbiting system the tangential velocity of orbiting bodies is slower for the bodies on the outskirts of the system so they experience less kinetic time dilation and also less gravitational time dilation than bodies orbiting nearer the centre of the system and again this is only really noticeable when really close to something like a black hole. A complicating factor is that most galaxies there appears to be dark matter (mass not directly observed in the form of stars) and this causes the tangential velocity to be nearly constant for all orbiting bodies in the disc except those really close to the centre. (It is this odd constant velocity that first alerted physicists that there must be a lot more mass in galaxies than is accounted for by counting visible stars. What form dark matter has is still a bit of mystery which cosmologists are busy trying to hunt down. If you are interested in dark matter you should check out the cosmology forum of PF (or google).

So as Ich suggested, from a purely general relativistic point of view any civilizations on the outskirts of the galaxy have a higher probability of being more advanced than those nearer the centre. If a remember correctly the Earth and the Solar system are only about midway out on the disc of the Milky Way Galaxy.

However, things are hardly ever as simple as first appears. The time dilation effect is not huge in general for galaxies (except really near a black hole) and astronomers hardly ever take the effect into account when accessing the relative ages of stars in a galaxy. A prerequisite for life and civilisations in general that are anything like us is to have a star to provide energy and possibly a planet to provide the chemical that are building blocks of life. So the most advanced civilisations would probably be in a region where the oldest stars are. Surveys of galaxies show the oldest stars are usually scattered about in the halo above and below the obvious disc. These stars formed when the galaxy was very young and are unlikely to have planets because they have low metallicity. The next most likely spot (ignoring time dilation issues) is near the centre. Stars here formed early on and some large ones evolved very quickly (because of there large mass) and created all the various chemicals that we consider essential for life before dying young in as a supernova explosion and shooting out all the various elements required to form planets and the atoms that make up life like you and me. Some of these elements ended up in the gas that created newer stars and astronomers can detect the "higher metallicity" of the stars that formed from this enriched gas and it is one way they estimate the age of the stars. From this information they have noticed that the younger stars are usually on the outskirts of the disc and in some cases this star formation process is still ongoing. However, I think it fair to say that physicists are not 100% sure about the way galaxies form and whether they form from the inside out or the other way round. I think on balance the astronomy evidence suggests the oldest stars (and possibly the most advanced civilisations) are nearer the centre while time dilation suggests the opposite. Of the two, I think time dilation considerations are less significant and dark matter probably makes time dilation even less significant.

5. Aug 21, 2008

### northcave

hmm interesting..

ok,,, so its not directly proportional. So if we travel to say Alpha Centauri which is what 4.5 light years away at light speed then it takes us 9 years to get there and back. Or at least 9 years to those on our planet.

At exactly light speed would time stand still or just be very slow?

The space ship you're in would obviously stand still in time as well then.... now if that happened all computers would stand still,,, so does that mean that anything that reaches the speed of light can't then slow back down? Or at least slow down by itself?

Obviously a meteorite in the way might well bring something to hault though.

Again sorry for the obvious questions.

6. Aug 21, 2008

### yuiop

At exactly the speed of light time does stand still, but no object with rest mass such as a rocket or an astronaut can get to the speed of light, not even in principle.

However, at very, very close to the speed of light the time that passes on the spaceship could be much less than the 9 years that passes on Earth, but it can not be be zero time.

7. Aug 21, 2008

### northcave

So the problems of ever reaching a nearby solarsystem and coming back to report on it are pretty much out of the question. Even if you did travel at near the spead of light to somewhere 100 light years away and came back anything could have happened.

So is there anything in science / physics that could in theory suggest another way of travelling large distances without the problems of relative time?

8. Aug 21, 2008

### yuiop

Yep, the absolute minumum time it would take to get there and back would be 200 years so even though you might only have aged by a couple of years during the voyage, everyone you left behind would probably be dead by the time you returned, (unless anti ageing skin creams have improved a LOT by then ;)

There are things that have been suggested to get round the light speed limitation, but as far as I know, none of them would be considered as accepted physics so it would probably be against the rumes to discuss them here. You could google for "Alcubierre warp drive" as a starting point and do your own research. Perhaps someone could advise if it is permissable to discuss that drive here?

9. Aug 21, 2008

### northcave

arr yes the realms of speculation. I can see how that might not go down too well here... however my interest is in practical application, theoretical or not, hence the questions.

Thanks all the same kev