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K Nixon

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  1. The model of this is that its a bit like dropping a bowling ball on the bed. A nearby marble would roll downhill towards the bowling ball as your duvet becomes curved. Of course this explains nothing because the model actually uses gravity to make the marble roll 'downhill'. The issue is that we are using the duvet to describe 3D space bending in the 5th dimension (space time) modelling it as a 2D surface bending in the 3rd. In the real situation there is no 'downhill'. Our heads cannot imagine the real thing. All other forces are modelled using exchange particles. Quite literally they fire particles at each other on order to exert a force. Gravitons are the theoretical equivalent for gravity but we have yet to discover them. (we seem to have stopped looking mostly) It was thought at one time that this curvature of space time could be caused by streams of gravitons (nicely described in EventHorizon if you like your scary films). But we continue with our search for models to adequately describe what gravity is - what it is that actually exerts that force. There are layers and layers of models and none of them quite do the job. Maybe we don't actually understand what gravity does yet and that's why we can't model it properly. Kieron
  2. Is Purpose not a human invention? It goes back to the need to create a deity- we all did it at some point in our history (not wishing to spark a god debate here - its just that all cultures created a god of sorts either because they each felt they needed one to give them purpose or because they each had good reason to create one - please don't start arguing the god thing! its a debate that never ends well.) Things are. They just are. If you need a 'because' it comes down only to 'because they happen to work. If they didn't work they wouldn't be here.' The idea is that all the constants that exist in the world (gravitation, permattivity of freespace, etc etc) could take any value. The values they take in our universe happen to allow things to work just nicely, gravity is strong enough to hold stars together and various factors allow nuclear fusion to happen etc etc we are here to talk about it. If one of them was too big or too small stars wouldn't work (or anyone of a multitude of other things wouldn't work) and either we would't be here to wonder or dimension would not be stable enough and the universe would have failed and ceased to exist. For those more sci-fi-esque thinkers out there, consider that a multiverse exists where each possible combination of values exists for each of the constants. In some combinations the universe fails to initialise while in others it thrives. Maybe in some it limps along with gravity that is too weak or a speed of light that is too slow. Either way it is like survival of the fittest on a universal scale. Who knew Darwin was a closet cosmologist... Kieron
  3. The Hubble constant describes the rate of expansion of the universe. It varies but it is about 70 km per second per megaparsec. That means for every million parsecs, space is expanding away from us at a speed of 70 km per second. This is quite unnoticeable on local galaxy scales. The milky way is 30-37 000 parsecs (0.037 Megaparsecs) across so the expansion would be negligible when measured against the usual speeds of stars and planets zooming around each other. It is 0.66megaparsecs to Andromeda so thats why even on a local galactic scale the normal speed at which galaxies bob around is not really affected by the rate of expansio (hence Andromeda is still coming towards us despite the universe' expansion) So whether expanding or contracting you would not notice a particularly great effect on the size of an individual galaxy. However I have to presume that you would when we start getting so small that we run out of space, we would start to notice something. I have a feeling that the Hubble constant may be linked to the size of the Universe and that it changes over time? I would not swear to this though, maybe someone knows more about this? Kieron
  4. Interesting New scientist articles on this if you can get hold of the last week in Aprils copy Kieron
  5. I wish I could remember who to credit with this (might have been John Gribbin?) but the best description I ever heard was that it is not that things are moving apart but more that the space between them is getting greater. Think of this like a large funnel with water being pumped in from the bottom. things are floating on the surface of the water. As water is forced up from the bottom, the surface they float on becomes bigger so they get more spaced out but they are not moving apart, its just that water is being forced into the gap between them. If you use the model of space time - it is stretching creating greater dimension between the objects in space, but they themselves are not moving apart. Things like redshift still work with this model, the difference being that the stretch in the emitted wavelengths is not caused by relative separation velocity but by the wavelengths becoming stretched over time as the space time onto which they are written is being stretched. Basically galaxies just bob around a bit and orbit each other while the universe forces more dimension in between them. This is one possibility. The universe is shaped a bit like a 'snakes' universe on your mobile phone - sort of wrap around. If this isn't the case and there is an 'edge' you are still quite correct that it is beyond our ability to reach. Although this somewhat goes against what I said above (these things are all just theories and change every few years depending on the latest measurements) but dimension (space AND time) only exist when matter or energy occupies the space. Following this the very first photons are travelling outwards at the speed of light creating new dimension as they go. If you 'stood' at the endue of the universe and the stepped forwards you would created space and time as you went as you now occupy that space. All of which is academic as we will never catch up with the photons travelling at the speed of light creating this edge of the universe as we go. Which version of the Universe's shape we use depends on the density of matter contained within it and it is this which changes. It is also linked to the fate of the universe - whether we expand for ever or go for the big crunch. Kieron
  6. i wondered about the Celestron ones, but at 84 quid the revelations sound like a good way to go. interestingly, thanks to this Todmorden break in (hope they get the beggars) and the American Astronomy Magazine I bought accidentally (I missed the absence of the word 'now' - still it was an interesting read) - I have discovered the existence of reflector binoculars!? I don't know what sort of size the Todmorden ones were but the ones in the mag had a picture of a woman sat in-between them with a binoviewer and what looked like a pair of newtonian reflectors pointing away behind her In all honestly she looked ilke a hobbit with a pair of field binoculars - I have never seen anything like this before. Having a club linked to a school means I am in the lucky position of being able to apply to the IOP for grants for astro equipment (waiting to hear on the first round of applications - fingers crossed) but now I have discovered these impressive looking sets I might already be formulating a list for next year! Will have to do some research on these bigger ones. Don't suppose anyone has any experience of these larger sets? Not the Hobbit making variety necessarily - thats probably a bit OTT. Kieron
  7. Have forwarded your list onto all on the mailing list at my astro club, can I encourage you all to do the same at your local clubs. Good luck.
  8. Hi Sparkly, No it doesn't lose energy as it actually doesn't have any energy. It is only a field - essentially a way of modelling where mass has an effect. If you put an object in that gravitational field it has gravitational potential energy. Now if that object moves towards the source of the gravitational field (like moving an asteroid toward a star) the object has loses gravitational potential energy, but like any object falling down, it will get faster and the lost gravitational energy becomes kinetic energy so the total energy stays the same! I do like physics sometimes. you can never lose energy. or indeed gain it. except if you're a virtual particle, but we don't talk about those, they mess things up Kieron
  9. I noticed a crack in the cloud a couple of days ago so stuck a scope outside that needed testing (new club one). I just picked a bright star at random to zero in the spotter a little. I hadn't quite left it long enough to cool so the view was a little changeable as it was and no matter what i did I just couldn't get this star to focus right. there was always a line across it. Eventually i hit the focus sweet spot and realised the darn thing had rings... then the clouds came, but it was a lovely clear here last night too so I got the scope out again. I was supposed to be testing the goto on it. I didn't. I just got it tracking about right and then sat and stared at Saturn for an hour and a half (I've never seen it through a scope before, new as I am to all this) With a glass of whisky in one hand this was the highlight of my week off. I didn't put it to the wife quite like that however... Kieron
  10. lidl/aldi one of the two has some 10x50s in for £17 so going to give them a go!
  11. Right. I won't go out of my way for them then, but I will keep an eye on ebay. cheers! K
  12. Questions about time crop all the time in lectures and lessons. I always give the quote (yet I have no idea where I got this from so sadly cannot reference it - if you know, please tell me!) 'Time? Well it's just natures way of stopping everything happening at once' My favourite fact about time is that it is not continuous but like most measurable quantities it jumps along in quantised little chunks! K
  13. I stand amazed. very clever indeed. Thank you very much! K
  14. Thank you tetenterre, that is a brilliant summary! K
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