Universe

[Naemeth]

There could well be some large things outside the Kuiper belt, but I think they'd be unlikely to be classified planets. They would probably have very eccentric orbits, they might be in hydrostatic equilibrium, but probably wouldn't have Cleared the Neighbourhood. I'm sure there are loads more 1000km sized objects to be found around the solar system, but I'd be surprised if we found something the size of one of the gas giants.

It would be rather fun explaining it if we did though!

It could be the "fifth" gas giant though. Yes, it would probably have an eccentric orbit, unless by clearing it's neighbourhood it in turn made it's orbit circular, although I'm not sure entirely how this would work, as a gas giant would take a huge amount of energy to change it's orbit. It could explain why comets like Halley's Comet have such odd orbits.....

Then again, this is all speculation, we aren't even sure the Oort Cloud exists, and even if it did, it wouldn't be strongly gravitationally bound to the Sun at all. If it does exist though, do all stars have a similar surrounding?

[Treeden]

... Graphic portrayals of the big bang as an explosion seen from the outside have a lot to answer for because those who create them fail to realize the meaninglessness of portraying them from the outside.

Olly

That's very interesting Olly. I tend to take these graphic portrayals (especially those in scientific documentaries like Horizon etc) at face value, but thinking about it, yes, they do tend to show the big bang as an explosion seen from the outside. Maybe we are tripping over our own feet in our desire to inform and educate?

The obvious question that follows is how would you create a more accurate cgi animation of the big bang, from inside and within the explosion? My first thought was something like the acceleration to warp speed that they use in the Star Trek films, the visually impressive combination of doppler shift and time dilation. It wouldn't be accurate though, because there is nothing to accelerate into! How would you show inflation from the inside? Maybe the viewpoint of the animation would have to be looking back? The more I think about it the more I can see why they show it from the outside!

[Ronnie67]

Wont it be great if they sent a satellite like the voyager to the other side of the sun and let that run its course, may be, just maybe there are other planets at the other end of our solar system which we have not detected, or even greater BH

[Ganymede12]

Just wondering, when we point at stars with our laser pointers or even torches or basically, anything that gives out light, do the photons from our torches or lasers reach the stars eventually?

[Vince1963]

Very interesting Ganymede12. I like that ...But by the time it reached its target wouldn't the target have moved?

[Ganymede12]

OK, good point. But would it reach the space where the star Was and if so could you predict it where it would be in so many years time and launch the photons at where it's going to be.

Of course to launch the photons at polaris you just have to wave your laser around the area surrounding the star because polaris hardly moves at all (from our perspective.)

[ollypenrice]

That's very interesting Olly. I tend to take these graphic portrayals (especially those in scientific documentaries like Horizon etc) at face value, but thinking about it, yes, they do tend to show the big bang as an explosion seen from the outside. Maybe we are tripping over our own feet in our desire to inform and educate?

The obvious question that follows is how would you create a more accurate cgi animation of the big bang, from inside and within the explosion? My first thought was something like the acceleration to warp speed that they use in the Star Trek films, the visually impressive combination of doppler shift and time dilation. It wouldn't be accurate though, because there is nothing to accelerate into! How would you show inflation from the inside? Maybe the viewpoint of the animation would have to be looking back? The more I think about it the more I can see why they show it from the outside!

I wondered about how this might be done. I think that one of the great things that we have learned is that we cannot expect to visualize all of that which is true around us and we should accept that with modesty and good grace.

Today's cuttng edge thoeries are tomorrow's has beens? Not so sure about that. Sure, sometimes, but a better description of scientific progress is that theories become ever more generalized and de-localized. M and M set out to demonstrate that there was a luminifous ether. They ended up demonstrating that there wasn't one. 'And I think this is good!!'

Olly

[Naemeth]

I've another question..

If Gravity causes celestial objects to collapse under their own gravity and form a near-perfect sphere, why is the Universe not a near-perfect sphere?

[JulianO]

I've another question..

If Gravity causes celestial objects to collapse under their own gravity and form a near-perfect sphere, why is the Universe not a near-perfect sphere?

Things only collapse to form a sphere in the absence of anything else going on. If the constituents are moving fast enough they don't form into anything, unless they can somehow lose their energy.

So for quite a while this was an open question - was there enough mass in the universe to say that eventually it would be enough to bring everything back together again and form a singularity. It turned out that there wasn't and when looked at more closely the force of dark energy was pushing the universe apart faster and faster, so there are no sphere's in our future.

[Vince1963]

I've another question..

If Gravity causes celestial objects to collapse under their own gravity and form a near-perfect sphere, why is the Universe not a near-perfect sphere?

Well i agree with you...I think if there is an outward force such as an explosion this surely would be uniform in all direction which in effect would be spherical in a vacuum , unless the object in question was sat on a flat surface (or against some other body) then the outward force would be deflected and no one knows the future of the universe it could eventually slow down to a stop and then start contracting at a super fast rate. the end result would be a sphere.. Right?.. that is until it imploded on its self and started the cycle again.

[Vince1963]

So for quite a while this was an open question - was there enough mass in the universe to say that eventually it would be enough to bring everything back together again and form a singularity. It turned out that there wasn't and when looked at more closely the force of dark energy was pushing the universe apart faster and faster, so there are no sphere's in our future.

But Dark energy is still far from being understood right?

[Cath]

But Dark energy is still far from being understood right?

That and many other things Vince

Basically when they say 'Dark' - as in Dark energy and Dark matter it just means they don't know, it's just a 'filler' description until they start to come up with possible theories for what's happnin.

[ollypenrice]

A thought at this point; scientsts are sometimes accused of claiming to know everything. (I have never met one who did this but journalists seem to meet them all the time. No comment.) But if they say that they don't know everything, which is what they say all the time, the public can sometimes jump up and down in a frenzy of excitement shouting, 'They don't know, they don't know!'

This is an astronomy forum so I think we should be above the sillier aspects of this public situation. I'm not for a moment saying anyone so far is not above it, I'm just ruminating aloud...

Olly

[Cath]

A thought at this point; scientsts are sometimes accused of claiming to know everything. (I have never met one who did this but journalists seem to meet them all the time. No comment.) But if they say that they don't know everything, which is what they say all the time, the public can sometimes jump up and down in a frenzy of excitement shouting, 'They don't know, they don't know!'

This is an astronomy forum so I think we should be above the sillier aspects of this public situation. I'm not for a moment saying anyone so far is not above it, I'm just ruminating aloud...

Olly

awwww Olly

[ollypenrice]

Cath, my comment certainly wasn't aimed at you! I entirely agree with your term 'filler description' and suspect that it could just as well apply to most scientific desriptions including the mature ones. Science offers us the best model we have, but it's an evolving model. That's all I meant.

Olly

[Cath]

Cath, my comment certainly wasn't aimed at you! I entirely agree with your term 'filler description' and suspect that it could just as well apply to most scientific desriptions including the mature ones. Science offers us the best model we have, but it's an evolving model. That's all I meant.

oooohhhh coool. Thought maybe I'd put my foot in it - again

[Cath]

Some might find this interesting ...

http://www.muppetlab...box/txt/al.html

http://math.ucr.edu/home/baez/physics/index.html

[DarkStar7]

Doesn't anyone see a connection between lost information into BHs and the accumulation of information in space-time pushing it apart. Entangling all singularities of BHs at all scales seems a good idea to me.

[Ronnie67]

At the center of a black hole the singularity point has zero volume and infinite density. I know that the singularity is a point in space rather than an object with specific dimensions, but how is it possible for something to have zero volume and infinite density?

The Answer

This is indeed difficult to grasp. Actually at the center of a black hole spacetime has infinite curvature and matter is crushed to infinite density under the pull of infinite gravity. At a singularity, space and time cease to exist as we know them. The laws of physics as we know them break down at a singularity, so it's not really possible to envision something with infinite density and zero volume. You might check out the web site for further information on black holes and singularities:

http://antwrp.gsfc.nasa.gov/htmltest/rjn_bht.html.m.

[jflowers]

At the center of a black hole the singularity point has zero volume and infinite density. I know that the singularity is a point in space rather than an object with specific dimensions, but how is it possible for something to have zero volume and infinite density?

That colour font is a singularity! May just be me but I cant read it and it hurts to try....

[Cath]

The laws of physics as we know them break down at a singularity

It always seems strange to me when it's put like that. I think a less misleading way of putting it (for those just starting out) might be something like 'our theories fall apart' rather than 'the laws of physics as we know them break down'. The Universe is just doing what it does, whether it follows our thunked up laws or not.

Sorry, just being me - again

[Ganymede12]

I read in one book that when the universe "ends" it will collapse in on it's self and a second big bang will occur creating a new universe with completely different physics!

The book I was reading was old so does this theory still stand or has it been replaced? What about the big chill? (every thing is so far apart that the universe becomes cold) Has that replaced "the big crunch" or will they both happen?

[SionR25]

I read in one book that when the universe "ends" it will collapse in on it's self and a second big bang will occur creating a new universe with completely different physics!

This is still a possibility but recently it has been discovered the expansion of the universe is accelerating, due to dark energy, and not being slowed down by gravity as we thought it might. Because of this we think it is more unlikely the universe will collapse back in.

Sion

[jflowers]

I read in one book that when the universe "ends" it will collapse in on it's self and a second big bang will occur creating a new universe with completely different physics!

The book I was reading was old so does this theory still stand or has it been replaced? What about the big chill? (every thing is so far apart that the universe becomes cold) Has that replaced "the big crunch" or will they both happen?

I prefer Douglas Adam's thoughts...

There is a theory which states that if ever anyone discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable.There is another theory which states that this has already happened.

[Ganymede12]

I've seen that quote in someone's signature.