OT: Expanding universe question.

Maybe not the right place to ask. Or maybe exactly the right place to ask, since I think there are some here interested in this sort of thing? Anyway, be gentle with me :-) We're told that nothing can exceed the speed of light (maybe that's an oversimplification for idiots like me). We're also told that the universe is exanding (again, maybe that's an oversimplification etc.). Now, the universe is rather big, so it seems to me that two things on opposite sides of it could /easily/ be travelling away from each other faster than the speed of light. The only way I can resolve this is to imagine that actually it's space itself that's expanding, and if you had some sort of cosmic tape measure, then you wouldn't measure any movement at all. Is that 'really' what's happening? Is the universe not expanding in what I think is the conventional sense? Everything I can find to read about it just says it's expanding, and doesn't go beyond that.

Reply to
Dan S. MacAbre
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No. Its all pictures in your head trying to make sense of sensory data, up to and including dials moving and digital data.

The greatest mistake that nearly everybody makes in this life, is to confuse pictures in their heads with what's really there.

Ok we cant relate to what's there without pictures in our heads., but the problem only arises when we regard those pictures are real in themselves, rather than a 'story about life, the universe and everything'.

Calling a bolt of lightning an electrical phenomena rather than a God's missile, may yield some interesting predictions about how it behaves, but it doesn't make it any more or less 'true'.

AIUI, which isn't a lot, the 'universe;' is 'expanding' but the bits 'furthest away' are very very near the speed of light, so the signals from them are so deeply red shifted they are probably in the audio spectrum.

Reply to
The Natural Philosopher

It is expanding by stretching (like the surface of a balloon), and it is possible for objects to be receding faster than light, subject to various bits of hand-wavery about how you measure time and distance.

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Reply to
Halmyre

You just need to read up on Special Relativity and Inertial Frames.

Reply to
newshound

I used to watch 'Horizon' programs about this, until deciding they were all completely nebulous. Nice graphics and lots of filler. I watched some Brian Cox, until realising he'd gone all the way to Corsica or Sardinia just to tell us that everything is just 'moment in time', at which point I switched off. I tried reading Stephen Hawking, and it was pretty much the same. Weird 'facts' and no explanation. I got pdf files of Einstein's theories, and didn't get further than the 'Riemannian Manifolds' on page 1. I suspect it is completely beyond me, and I should just leave it at that :-)

Reply to
Dan S. MacAbre

Audio waves are not electromagnetic waves.

Reply to
Halmyre

Okay :-) I've nearly finished Zamoyski's '1812', then I'll find out what an Inertial Frame is. TBH, I think I just don't have the maths.

Reply to
Dan S. MacAbre

Amazing. Thanks.

Reply to
Dan S. MacAbre

Reply to
bert

Yes. Although you might get better answer on sci.astro or sci.relativity

The strict prohibition is on not being able to send information or move an object faster than the speed of light. There are circumstances for monochromatic light in highly dispersive media where the speed of light as a phase velocity is greater than c but the speed at which energy or information can be moved the group velocity is less than c. The crests of the waves move forwards faster than c, but the pulse of energy moves more slowly since the frequencies all interfere with each other.

Most of the claims of faster than light transmission stem from misunderstandings by engineers of this particular characteristic of electromagnetic radiation inside waveguides.

You can see a variant of this in the surface waves in the wake of a boat on calm water. The ripples move out at phase velocity but the outer edge of the disturbance expands at a different but linked group velocity forming a characteristic V shape.

There are parts of the universe that are moving apart faster than the speed of light but they cannot ever communicate or even see each other. In purely practical terms we can't see back past the surface of last scattering which is now redshifted to the 4K microwave background but when it filled all of space was around 4000K and redshift Z ~ 1500.

Essentially yes. It is the space in between things that is expanding so that redshifts are observed to increase with the objects distance.

The classic cosmic tape measure uses so called standard candles which are particular incredibly bright supernovae where knowing the light curve shape immediately tells you its absolute brightness.

Such Type Ia supernovae can outshine an entire galaxy for a few days and be seen over vast distances using big modern scopes.

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Depends what you mean by the conventional sense. The difficulty with understanding Big Bang cosmologies without detailed mathematics (and even Horizon regularly gets this wrong) is that most people imagine an explosion of a point in an existing spacetime at a given time whereas the situation in the mathematics is that there is no before and no space before t=0 (at least with the current Big Bang standard model).

Posting in d-i-y implies that you are considering making a universe. This is a considerable commitment and may rapidly outgrow your workshop!

Reply to
Martin Brown

The maths actually isn't that hard, you can probably find a good explanation on a university first year physics site. (It was A level in my day). See "closing speeds" in Halmyre's Wiki link. It's all about points of view!

Reply to
newshound

Does anything say its expanding faster at the edges? Is it accelerating?

It can quite easily be expanding forever and never get anywhere near the speed of light.

Reply to
dennis

That is why I try to insist that Korzybski's insight ("the map is not the territory") is perhaps the most condensed form of a metaphysical position that understands the notion that the world we deal with is a

*mapping* of what's really there, not what *is* really there.

Our whole world view is in fa?t a *theory* about what the world is.

And nearly all human conflict embodies some aspect of the fact that no two people have exactly the same pictures in their heads.

Science doesn't take us to the truth, but it does allow the worst and most useless ideas to be discarded and the ones that actually work, to be retained.

I've only met with one philosopher who seemed to really understand that and he's dead now. Hilary Putnam.

Reply to
The Natural Philosopher

They are when they come out of my guitar.

The 'audio spectrum' isn't the sound, it's the *frequency of sound*. Normally 20Hz-20hkHz..

Reply to
The Natural Philosopher

MM. You sort of don't need it.

An inertial frame is simply 'how stuff is when left to itself'

i.e. not accelerated. Or freely falling in a gravitational field.

Relativity IIRC simply states that you cant exceed the speed of light in one inertial frame, but of course there are an infinite number of inertial frames, and things in one frame may seem to exceed the light speed when viewed from another.

But I am not an expert so don't call me out on that explanation.

What you have to understand that what relativity did was blow the idea of 'one space, absolute in dimension;' out of the water.

Rather we have space created by mass. with mass being a form of energy.

So mass/energy/space/time becomes a rather crappy way of looking at something, that we don't really understand.

Penrose gets easier to read when you realise the maths is just 'ways of describing stuff we don't understand' and try not to worry about whether what it seems to say in terms of what is 'really there' is apparent nonsense or not.

Personally I like to think of the world of our perceptions as something like an intersection of 'whatever is the case', with our consciousnesses.

The pictures so produced owe as much to our consciousness and its nature as they do to what is 'really there' whatever that means...

And that's why Gods appear and are anthropic. They are what we stick over the great mystery of the fact there not only is there a universe, but we seem to be aware of it, and of ourselves as beings who are aware of it. That is a very very strange fact.

And that goes back to the original post.

What is *really there* is not only unknown, but it is also in the limit unknowable.

Even if we were completely detached from it and could measure all of it to infinite decimal places, we still would be leaving out one enormous elephant in the room, ourselves. Or at least out conscious minds.

Our very understanding of the basic nature of the world is ultimately pretty much a Judaeo Christian one (I would include Islam, but its really not up there, philosophy wise) that is, we are able to be 'detached observers' of phenomena precisely because we understand the notion of 'pure spirit' or 'holy ghost' (consciousness) as distinct from 'the material world' of e.g. physics.

Reply to
The Natural Philosopher

You could have a look at

I never managed the maths the cosmologists tossed around but things like "raisin bread model" can help. Especially if you get to eat the bread for tea afterwards.

And don't let comments here put you off having a go at DIY. You are at least starting on a Monday which many consider to be the traditional day to kick off the job. And it's one of those jobs where you can take some comfort from the fact that if it goes *badly* wrong chances are no one will ever know ;)

Reply to
Robin

Rodders creates a new universe very time he opens his eyes.

Reply to
The Natural Philosopher

Martin Brown explained on 24/10/2016 :

Reply to
Harry Bloomfield

*Very* rapidly, if cosmological inflation is correct.
Reply to
Huge

The maths is a little tricky, for me it was first year university in applied maths. I'm surprised it was taught at A'level physics.

Reply to
Nick

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