Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Geezer on 09/02/2010 21:25:42

Title: Am I relatively smaller?
Post by: Geezer on 09/02/2010 21:25:42

OK  - no cheeky comments if you please!

It is well held that matter "distorts" space, or spacetime if you prefer. We are familiar with the well documented effects this has on relative time, but does it also mean that, in relative terms (naturally), my "size" changes as I experience different gravitational fields?

Obviously this would be difficult to measure because any measuring instruments would be similarly affected, but is it true in relative terms?

Title: Am I relatively smaller?
Post by: LeeE on 09/02/2010 22:23:46

It would seem so, in relative terms, but I don't think it's as simple and straightforward as it might seem.  If you think back to time dilation you need to remember that despite existing in different elapsed times, both the stationary and the moving bodies simultaneously exist at the same point in asymptotic time: if they did not then the body experiencing a relative slowing of time would seem to disappear and 'pop' out of existence to the body that is not experiencing time dilation because the slow running body has not yet reached the time at which the 'normal' body now exists i.e. after starting the clocks running at the same time, the 'normal' running clock is now at 12:30 whilst the moving clock might only be at 12:15, thus the moving clock doesn't yet exist at 12:30.

Title: Am I relatively smaller?
Post by: yor_on on 10/02/2010 01:28:17

It's correct as far as I know, although you won't notice it.
As those binary stars or black holes whatever :) rotating around each other can create 'gravity waves'..

Need a proof?

Look here, yep, its passing your screen just now..

(https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.aei.mpg.de%2FeinsteinOnline%2Fen%2Fimages%2Felementary%2Fmandala_gw.gif&hash=129e1a8063e48576afcf5ab2f3196101)
Gravitational waves (http://www.aei.mpg.de/einsteinOnline/en/elementary/gravWav/rhythm/index.html) and here 2 (http://www.einsteinathome.org/gwaves/index.html)

==

One reason why you won't notice it, amongst others, is that they become incredibly weak at the distance they have to travel to us. " True, a supernova explosion in a nearby galaxy will produce, within the first few seconds, the energy of a trillion sextillion nuclear explosions, with much of that energy radiated away in the form of gravitational waves - but on its way to earth, all that energy dilutes to a pitiful remnant wave, changing the distance between the earth and the sun by the diameter of a hydrogen atom, at best."

Then there is the discussion of how fast they travel too :)

Title: Am I relatively smaller?
Post by: Geezer on 10/02/2010 06:14:50

Yes! Yes! That's exactly how I feel! Sometimes I put on weight, then sometimes a stretch out a bit.

Eh, but maybe I didn't ask the question very well, or maybe I don't really know what the question is.

I was not thinking of wavy gravity, I was thinking of static gravity.

Let's say I travel into a region of space where there are no strong gravitational fields. In that region of space I imagine space is nice and uniform. A cube of space is actually, like, cubic.

When I travel back to Earth there is a reasonably strong gravitational field. In that region of space I imagine space is no longer nice and uniform. A cube of space is anything but cubic. Of course, it's impossible to determine that, because any measurements we make on Earth will assure us that the cube is actually cubic.

I suppose the only way to determine the difference would be to view the two cubes from far away and compare them, but it's not clear to me that would be valid or meaningful.

So, if gravity distorts space, I'm assuming it distorts everything in that space too, even though it may be impossible to observe the distortion. Or is it just my mind that's distorted?

Title: Am I relatively smaller?
Post by: Farsight on 10/02/2010 07:45:07

Your mind isn't distorted, geezer. A static gravitational field will distort your cube to make it a little flatter. Search google on radial length contraction (http://www.google.co.uk/search?hl=en&source=hp&q=radial+length+contraction&meta=&rlz=1W1ADBF_en-GB&aq=f&oq=) to find out more. But like you said, everything is distorted, so you can't measure it locally. See Flatland (http://en.wikipedia.org/wiki/Flatland) for some conceptual grasp of this.