Stephen Hawking's Universe

[vlebo]

Maybe it's because I am tired but I am a bit confused. I am watching Stephen Hawking's Universe and in it he states that during the creation of our universe "by the time the cosmos was ten minutes old (after the big bang ) it was already 1000's of light years in diameter ".

This is were I get a bit lost as I thought nothing travels faster than light so how can anything be 1000's of light years across in ten mins.

Please forgive me if the answer is glaringly obvious but I cannot get my head around that statement. Maybe I will tomorrow after a good nights sleep but somehow I doubt it.

[david o]

From the little I've read and the even less I think I've understood:

Nothing can move faster than light within the universe, but the universe itself can expand faster than light, what cosmologists call inflation.

Don't ask me how or why, but apparently it involves the so called "dark energy".

[calibos]

Its also the same reason that we can only see about 14 billion lightyears in all directions despite the fact that it is estimated that the universe is in fact anything from 40 billion lightyears to god knows what across(then again across means nothing when one visualises something expanding into nothingness )

ie. the universe maybe 40 billion lightyears across but seeing as the universe is only 14 billion years old only the light from that far away has had time to reach us.

Also we can never see beyond that distance because although light from a given invisible galaxy might be coming towards us at light speed, the space in between us is stretching at what is for all intents and purposes is faster than light speed. The analogy is one step forward, two steps back, for the light coming from that invisible galaxy beyond our 14 billion year universal event horizon.

It all basically boils down to this strecthing, inflation, expanding of space or whatever you want to call it.

It helps to visualise space as a 2 dimensional rubber membrane which helps to visualise a lot of the incomprehensible(to non maths brains like myself) weird stuff in the universe.

EG. Gravity isn't some invisible force that grabs things. Anything with mass creates a dimple in space, the rubber membrane. Think of the planets as various size and weight ball bearings sitting on a stretched out rubber membrane. They create dimples in space. Launching the Voyager 1 probe to Saturn and then onto Uranus and Neptune was in effect a very complicated and accurate rolling of a small marble over that rubber membrane towards Saturn, just catching the edge of the dimple which swings voyager off in another direction towards Uranus and then using the dimple in space around Uranus to swing the marble/Voyager off towards Neptune. Putting something in orbit around Saturn like the Cassini probe is rolling the marble in such a way that it isn't just catching the edge of the dimple but actually gets caught in the dimple in space and rolls around the Saturn Ball bearing like a ball in a roulette wheel.

In terms of the big bang and expanding space it helps to visualise the universe as another rubber membrane. GLue a few marbles to represent Galaxies all over the rubber membrane. Now start pulling/stretching out that membrane in every direction. None of your marbles are actually moving but as the rubber membrane stretches in every direction at once, every marble fixed to the membrane gets further away from every other marble. Its the membrane/space that is stretching between every marble galaxy.

The rubber membrane analogy even works for blackholes. I couldn't visualise a force reaching out and pulling on massless photons of light. I couldn't grasp how light couldn't escape black holes. I was understanding it all wrong.

The mass of a black hole twists spacetime around itself. Its like a really uber heavy little marble sitting on the rubber membrane in its domple and me grabing hold of the marble underneath and twisting it around and around, pulling in and wrapping more and more of the rubber membrane around the marble. Imagine light can travel 3 inches along the rubber membrane per second. However as I twist the membrane around the marble I am pulling in 4 inches worth of membrane per second. ie. a black hole is twisting in space around itself faster than light can travel through that amount of space. Thus the light can't escape being pulled in too along with the space.

Its this dimple and twisting combination that every mass creates in space that deflects light too. IIRC one of the proofs of Einsteins theories was wacthing a backround star being occulted by the Sun. According to the theory we should be able to see the star for a split second after it actually disappeared behind the sun. The theory said the gravity/twisted dimple of the sun would bend the light coming from the star behind. Kinda analgous to a straw in a glass or the atmosphere bending the light from below the horizon that you can still see just above. Thats why one shouldn't us Sirius for example as an alignment star when setting up your scope. The closer to the horizon the more light is refracted by the atmosphere. In reality, Sirius isn't exactly where it looks like it is if you get me. Now thats refraction nothing to do with einsteins special relativity but it helps to visualise it. In terms of the proof with the bacground star and the sun. The light from the star travels through space following the contours of space as it were. If space is twisting/bending around the sun a little then the light traveling trough that bit of space and is bent along the twist too.

Druid, I just read some of that in a book someone else wrote. I am probably explaining it arseways anyway!!

[bing434]

That's a nice way to describe it. Helps simpletons like me anyway haha - you should write a book about it!

[vlebo]

mmmm