if the universe is infinite which I always thought it was as if there isn't a universe there isn't anything why..

[Ormirian]

Prof Cox insists on talking about hundreds of billions of galaxies. Because even a 1000000000 is a number and it isn't infinity.

He keeps using these BIG numbers but surely all he needs to say is 'an infinite number' or even 'lots and lots'. Both of which are more correct.

AIBU?

On that note, I have another question.

The universe is apparently about 13.9 billion years old. However, the most distant object we can see is UDFj-39546284, which is circa ~31.7 billion light-years away, and as we see it now was apparently 13.2 billion ago. I know I'm not a PHd in maths, but that don't add up.

The universe would have to be constantly expanding at faster than the speed of light in order to achieve this size; and that's assuming we were at the centre (which we are nowhere near).

Oops, sorry. I meant assuming that we were on the outer edge. EI, 15.85bn ly to the centre each. Assuming that we are not, the expansion is a hell of a lot faster than the speed of light, which I cannot be because the big bang was caused when the expansion of the singularity passed light speed and it cause a bloody big explosion.

theatomicbum: "However, the most distant object we can see is UDFj-39546284, which is circa ~31.7 billion light-years away, and as we see it now was apparently 13.2 billion ago. I know I'm not a PHd in maths, but that don't add up."

Unless the universe IS finite and that light is the light from our own sun travelling back to us?

< brain explodes, kenobi falls in heap >

Even so, the universe would have to be much larger than is possible. And there would have to be a reflection of everything going.

Unless the fabric of the universe could be thought of as spherical instead of flat? So that light would travel in a circles around the universe and everntually come back round? Like a plain going in a circles around the world IYSWIM?

But that would then leave the question of what the light is going around? I suppose there's enough mass in the universe to warp light on a grand scale. I mean, theoretically speaking.

[joins Kenobi in brain exploded heap]

Oooh I love this thread - it definitely expands the mind whilst cooking boring old lasagne!

Everything and Nothing on BBC4 at 9pm might be good.

I don't have bbc4

MooMoo your questions are not remotely ignorant, they are deeply profound.

kenobi well spotted. How can we see things that are more than 14bn lightyears away? Remember that space-time is expanding so that the distance of the furthest object is the distance now not the distance that the object was at the time that the light now reaching us was emitted.

Nappies not mallows! damn iphone

I love the idea of you trying to ignore profound questions of the universe by thinking about marshmallow, hogsback. How about kittens and glitter too?

'Raindrops on roses and whiskers on kittens
Bright copper kettles and warm woolen mittens
Brown paper packages tied up with strings
These are a few of my favorite things'

I want to understand this but I can't.

My 7 year old was asking me about black holes yesterday so I dilegently looked up the NASA site and read stuff to him.

He seemed to understand it. My brain melted.

GabbyLoggon: I think it's a little unfair to say the professional pretend they know the answers. We have some pretty good theories that have stood us in pretty good stead.

Gravity is only a theory, but using it, we can launch a satellite from Earth and predict to within a second when it will arrive in orbit around Jupiter, 600 million kilometres away. That's a pretty good theory.

Similarly, quantum mechanics is only a theory, but using it we can design transistors only a few nanometers across, pack over a billion of them onto a piece of sillicon the size of your little finger nail and stick it in the computer I'm using to type this. I'm sure you'll agree, a pretty good theory.

The theories that we base our view of the cosmos on have been tested and to the best of our knowledge we think they're broadly correct: the theory that relative speed distorts space-time (special relativity) has been evidenced by demonstrating that clocks run slower in fast airplanes compared to ones left on the ground, the theory that gravity distorts space-time has been demonstrated by the effect it has on the orbit of various planets and the effect it has on light coming from the Sun.

On the other hand there are lots of things where we don't have a consistent theory for that explains everything we see, and scientists are very open about it, some examples include:

• Why is gravity not explainable using quantum mechanics when all the other forces (electric, weak nuclear, strong nuclear) are?

• Where is the missing mass, without which we cannot explain the motion of galaxies using conventional theories?

• Why is the universe as we see it? The universe is largely 'flat', however even a very slight deviation in the initial conditions of the Big Bang would have resulted in a universe that was either so dense it would have collapsed back in on itself, or conversely expanded so quickly that galaxies would never have had time to form.

• Why are there only 4 observable dimensions?

Hogsback, I've never understand the gravitational effect of each atom is not quantifiable. Surely the affect is just cumilative based of the mass on the object? Even if the gravametric forces of 1 atom are instubstantially small.

I mean, surely its that very force that attracts the electrons to the nucleus of the atom, which would explain why the easiest way to explain the structure of the atom is the planatery model?

And if the affect continues to be cumilative, it would also explain why the universe didn't collapse in on itself, IYSWIM? The same as how conventional physics failed to explain why the electron doesn't collapse into the core of the atom?

There are very approximately 350 billion galaxies in the observable universe.

Didn't see prog, but aasume this is what he was referrring to.

There could be an infinite number of (unobservable) "universes" in what some people call a "multiverse".
Or there might be (far more likely) finite, but equally unknowable, number of such universes.

Also, I thought the "missing mass" had been explained? That where we used to think the universe was mostly empty space, we now understand that space is actually full of the tiniest subatomic particles (which I thought was referred to as the "God Particle" - meaning "oh god, when are we going to find that particle"), which, although so small we have no way of actually observing it, we believe it is makes up the majority of the universe?

Hogsback
www.amazon.co.uk/Just-Six-Numbers-Universe-Science/dp/0753810220/ref=sr_1_1?ie=UTF8&qid=1300791840&sr=8-1 is great and answers 3/4 of your questions and basically explains all the fine-tuning of the universe.

cumfy: with respect, no book answers those questions as they don't currently have an answer.

Surely everyone knows the universe is a hologram and we are but a computer simulation of sorts, makes perfect sense when you think about it

You know, the idea of gravity being the cumilative effect of the attractions of the neuclus would actually make sense, wouldn't it? If that took the place of the graviton?

Cortina, does that mean that you are just a charactor in the game? Does that mean that as we have developed the emergance properties of consciousness and free will that the program has evolved being the need to it to be considered to be a non-reality? In that case, we still exist whether physically or not, IMO.

Oh. I just realised that would mean the missing mass theory would be wrong . Unless the attraction took place with other types of partciles [happy]?

Hogsback

Re 4+ dimensions (at a macro level).
So what do you make of Rees's idea that:

atoms would be impossible in a universe ruled by an inverse-cube law, because there would be no stable orbit for electrons.

And it would explain why electromagnetism has an effect of gravitational forces, would it? If the electromagnetic forces were having effects on the neuclus' particles? Am I onto to something, or am I talking s*?

TheAtomicBun: taking your points in turn:

Yes, we could easily quantify the gravitational effect of an atom. It's simply a function of it's mass, which we know how to measure.

What we cannot yet do is describe gravity using the theory of quantum mechanics. These explains the forces of nature in terms of the exchange of particles, however the particles themselves behave in ways that cannot be described using classical theories. Notably, the particles can also behave as waves and it is this wave-particle duality that underlies quantum mechanics.

The classic example is light. Light behaves as a wave - it has a frequency and polarisation and other qualities of waves. However it sometimes also behaves as a particle (which we call a photon) depending on how you observe it.

This wave-particle duality, and the effects it has is very well explained by Quantum Mechanics, to the extent that 3 of the 4 forces of nature (the electric force, the weak nuclear force, and the strong nuclear force) can all be explained by this theory.

The stand-out is gravity. We have an excellent classical theory of gravity, general relativity. However, we have not yet formulated a quantum theory of gravity that demonstrated the effects predicted by general relativity. We've also never seen the theoretical force carrier particle, the graviton.

Physicists really don't like anomalies like this. It smacks of broken symmetries and lots of other things that make them itchy.

Regarding the missing mass, it is suggested that the universe is filled with a dark matter that we cannot see by normal means but can infer the presence of by it's gravitation effect on galaxies. The dark matter would have to be formed of WIMPs (weakly interacting massive particles). We're currently trying to detect these, but as they only very weakly interact with normal matter it's proving a bit tricky.

The "God Particle" that you refer to is the Higgs' Boson. It's a particle, the presence of which is predicted by the standard model, which has the special property of conferring mass. From mass, we get gravity, which is why it is considered pretty important. We haven't found one yet, but we're looking!