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Heads Up Jim Al Khalili on BBC4


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It was Fab, mind blowing and brought up some simple yet astounding facts that never crossed my mind. Loved it.

Matt

Edited by Vega
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Nice one for the reminder last night Kim, I completely forgot about it, only missed the first 5 minutes, I must say it was a really good watch.

Cheers

Simon

Edited by Si W
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Ive been downloading loads of old Horizons (including the Brian Cox ones, which are very good) but ive not been able to figure out if there is a certain time that these are regularly shown on the beeb.

Is there a certain time of week/channel that we should keep an eye out?

Jims series 'Atom' was highly enjoyable. (He travelled quite a bit in that one! Its not just Cox!)

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I was waiting for brian to join in - spot on mate - much more effective than the flowery (general public targeted) presentations on a sunday night lol :hello2:

That's the whole point though, the Brian Cox series IS aimed at the general public where as this show was aimed more for people on here! Both are excellent for their target audience. I feel BC is getting a bit of a raw deal from people on here!

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Just watched 'Everything' on the Iplayer and thoroughly enjoyed it although I won't pretend that I fully understood all of it.

The one thing that got me quite puzzled was the part at the end where he was explaining how at some time in the future, because the rate the universe is expanding is getting faster, the light from distant galaxies won't be able to outrun this expansion and will therefore disappear from view....

I'm sure I've heard Brian Cox proclaim that we know of nothing that can travel faster than the speed of light, therefore how can the expansion of the universe become so fast that it will be able to 'outrun' light?

I'm obviously missing something. :hello2:

Edited by lankywolf
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@zcapp yeah you're right - I wasn't meaning to criticise BC because I do actually like his easy going style and did enjoy the Solar System (even if his voice does grate after 8hrs listening lol) I merely meant JK was probably more suited to me content wise. :hello2:

@cash - thanks for reminding me - I was trying to remember what it was called - Atom was brilliant too :hello2:

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@Lanky - the only way I can think of it is that if light started at point A and we started at point B later on, then we must be constantly trying to catch the light up from point A as it accellerates away from us. Or is it the other way round .... lol :hello2:

Edited by brantuk
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Remember that with expansion the universe is not actually moving so there is no limit to the rate of expansion. if you have a metre of space and place points A and B either side and it expands to 2 metres over one hour then A is receding from B at 1m per hour.

If 2 sections of space were between A and B then they would be receding at 2m per hour as both sections would have expanded to 2m, giving a total distance of 4m from A to B.

If there are 1000000 sections of 1m space between them then they would be receding at 1000000m per hour even though each individual section is still only expanding at 1m per hour. There is no limit to the number of 1m sections of space between them so there is no limit to the expansion.

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So you're saying the distance between objects increased without them actually moving. So the light has further to travel at the same speed. That sort of makes sense. I think...

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I'm sure I've heard Brian Cox proclaim that we know of nothing that can travel faster than the speed of light, therefore how can the expansion of the universe become so fast that it will be able to 'outrun' light?

You can think of the speed of light decreasing - that gives a good mental model though it's not accurate physically.

Alternatively go back to the inflating balloon model. If a balloon is inflating at such a rate that a pair of points one millimetre apart doubles their seperation in a second, and the balloon is the size of the Earth (40,000 km in circumference), a pair of points in London and New York (5,000 km apart) will be moving apart at 5000 km/sec in the first second, 10,000 km/sec one second later, 20,000 km/sec two seconds later ... after only 6 seconds their mutual speed will have increased to 320,000 km/sec - more than the speed of light - so that they will no longer be in the same "universe" - yet neither has accellerated.

Einstein's Theory of Special Relativity says that objects cannot accellerate through the speed of light. It does not say anything about space being warped. Neither does General Relativity set a limit to the rate at which space/time can be warped ... this leaves a (rather improbable) loophole for the designers of a inertia-free "space warp drive" similar to that apparently used in the Star Trek series; "compress" the space ahead of the ship and "stretch" it behind and the ship can be propelled at limitless speeds through the cosmos without having to accellerate at all, let alone break the "light barrier" in its local space.

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way ahead of Wonders,

+1

Almost every time I watch an al-Khalili programme, I find myself thinking, "Why didn't I think of that? What an obvious and simple way to explain it -- consider it nicked for the next time I teach it."

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The inflation/stretching of the universe is 0.00755% every million years.

Using "compound interest" that amounts to a doubling every 9181 million years.

So, if something is that far away and it emits light "now" (meaning 13.7 billion years after the Big Bang measured where IT is), after 9181 million years it won't have reached us but it will have gone half way as the original distance will have doubled.

The light will then be in a similar situation with respect to us as before it started. It will again try to cover the remaining 9181 million light years. But as it gobbles up space, space keeps expanding so it will never get here.

(I hope that's right!)

Edited by themos
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I've never seen a more understandable explanation of General Relativity (still don't completely understand it though, and I had to get up in the middle of the night to read up about the space-time continuum). 

For the best explanation of GR that I've ever had read "Why Does E=mc^2?" by Brian Cox. It's the first time I've read and gone wow it's sooo obvious now. :D

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