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The Universe for dummies

  • dmolloy
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I watched a documentary last night - previously recorded on skyplus. It was not the first time I watched this particular documentary by Stephen Hawking concerning the Universe. Although I understand most of it, some parts start to melt my head, and worse than that, I find my mind wandering :unsure: to a point where the image of a clockwork monkey appears in my head bashing tiny brass symbols together.....is this normal?
For example: why exactly does time stand still on the event horizon of a black hole?
and if at the moment of the big bang there was a tiny ball of infinatly dense stuff about to go doo-lally, then was this internally not moving, and if it was, was that not a sequence of events - ergo time sequence.......arggggghhhhh....

Dear IFAS is there a book called the Universe for Dummies, just for me....or don't I have the brain smarts for this kind of thing :unsure:


signed
Very disturbed
Co Laois
9 years 11 months ago #95253

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Replied by mjc on topic Re: The Universe for dummies

I'm sure there are many that have tried to write such a book.

In answer to you question re time slowing down as one approaches the event horizon.

Consider a probe falling in and observed from a safe distance away from the event horizon. Consider that probe sending out data by radio transmission at a particular wavelength and corresponding frequency. The probe transmits its data in one second pulses separated by one second gaps.

Because the speed of transmission of electromagnetic waves (including radio) is constant it does not loose energy by being slowed down as the source of the transmission approaches a large mass (noting more and more energy would be required to resist the increasing gravitational pull). Instead the electromagnetic radiation looses energy through gravitational red shift by which the wavelength increases and the frequency of the electromagnetic waves decrease. Energy is the product of Planck's constant, h, and the frequency, f.

So as the probe gets closer and closer to the event horizon (and still transmitting one second pulses one second a part by its experience of time) the wavelength of its transmissions are stretched as per a distant observer.
By the time the wavelength doubles the distant observer would detect two-second long pulses. The wavelength approaches infinity as the probe is about to cross the event horizon corresponding to an infinitely long time to receive even one pulse.

Of course as wave length is stretched the distant observer would have to be retuning his receiver - but we can ignore that.

If time slows down for the pulses themselves then it should follow that the same is true of the gaps - but it might need an examination of the maths to really demonstrate that one - and I've never touched general relativity from the maths end.

Hope that helps
Mark C.

[Edit: if the original transmission from the probe was at 1MHz then there is one million cycles - peaks - per second - which in this case is the original duration of a pulse. When the signal is received by the observer the signal is red-shifted such that measured wavelength has, say, doubled and frequency halved, there must still be one-million peaks in the elongated pulse - so the pulse has to take twice as long in duration when received compared to what the transmitter experienced.]
Last edit: 9 years 11 months ago by mjc. Reason: Additional text highlighted
9 years 11 months ago #95255

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Replied by johnomahony on topic Re: The Universe for dummies

If you we're falling into a black hole holding a clock, you wouldn't notice any difference to the timing on your clock. For an observer outside the black hole, they would observe your clock slowing down. Clocks run slower in a gravitational field ( lower energy state).
This effect can be measured using atomic clocks on the ground and say in a airplane or orbiting satellite. The very small difference in gravity causes the clocks at altitude to run slightly faster. In fact this time effect has to taken into account on GPS satellites to give the correct location. Without taking this gravitational difference ( and relative motion) effect into the calculations, your GPS would be off by several kilometres per day.
I gave a talk at an SAC meeting a few years back on this topic - it's a bit counter intuitive, hence the cymbal banging monkey. ;)
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Last edit: 9 years 11 months ago by johnomahony.
9 years 11 months ago #95256

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Replied by dmolloy on topic Re: The Universe for dummies

kling kling kling kling kling kling kling.......it was just the point of the observers point of view it would never appear to leave that point - but stay there.

Does it appear to stop moving from the observers point of view? or if the viewer stood there for a long long time - it eventually would......kling kling....damm monkies again :laugh: :ermm:

Thanks for the answers, when people ask me what a black hole is, I generally give them the standard type answer but sometimes I think about how little I truely know about the phyisics of the thing
9 years 11 months ago #95258

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Replied by johnomahony on topic Re: The Universe for dummies

kling kling kling kling kling kling kling.......it was just the point of the observers point of view it would never appear to leave that point - but stay there.

Does it appear to stop moving from the observers point of view? or if the viewer stood there for a long long time - it eventually would......kling kling....damm monkies again :laugh: :ermm:

Thanks for the answers, when people ask me what a black hole is, I generally give them the standard type answer but sometimes I think about how little I truely know about the phyisics of the thing


From an outside observers point of view, your clock would appear to slow down enormously to the point where it would appear to stop. However, from your point of view, time would appear to pass normally (apart from being reduced to a stream of elementary particles) :P
This is a real effect.
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9 years 11 months ago #95259

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Replied by RandomPillars on topic Re: The Universe for dummies

Oh god yes, I know the feeling. Haven't spent about the last year listening to lectures, podcasts and watching documentaries about cosmology from the likes of susskind, hawking and kaku- I now am the proud vessel of one such monkey. I call him Buttons.

To be honest, I actually don't think I have the concentration skills, education or intelligence needed to fully understand what these people waffle on about. Sometimes they produce an analogy that I can get to grips with but then they will follow it up with something else which I think completely contradicts what they just explained, so Bubbles comes back in, smashing his way through the dull bits of grey matter in my skull that are destined never to be used to their fullest potential.

Sean
"... quit trying to upset and disturb Dr. Venkman..."
9 years 11 months ago #95265

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Replied by albertw on topic Re: The Universe for dummies

To be honest, I actually don't think I have the concentration skills, education or intelligence needed to fully understand what these people waffle on about. Sometimes they produce an analogy that I can get to grips with but then they will follow it up with something else which I think completely contradicts what they just explained, so Bubbles comes back in, smashing his way through the dull bits of grey matter in my skull that are destined never to be used to their fullest potential.


This stuff is complicated, and takes quite a bit of mathematics to get to grips with. Some things can be simplified down with analogies, but they never capture everything, and more often than not lead to contradictions if you follow them through! They are all 'lies to children'. So even if there was a dummies quide it won't help, if you don't understand it you are still in the same position, and if you did understand, well, you didn't :)

What you need to do to try and get a better understanding is get gradually more scary books. Unfortunately this will lead to the situation you describe of going slightly insane :)

While not a 'for dummies' book, Kip Thorne's 'Black Holes and Time Warps' covers the topic very well. And a good book on relativity would have to be Einsteins own 'Relativity, The Special and the General Theory'.
Albert White MSc FRAS
Chairperson, International Dark Sky Association - Irish Section
www.darksky.ie/
9 years 11 months ago #95269

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Replied by RandomPillars on topic Re: The Universe for dummies

Thank you,

Yes, I will get that book by kip Thorne. I do have quite a few books that I have to get through (quantum mechanics and parallel universes) but I know I need to really start at the beginning and work my way up. All the books I've read are introductory into their specific field but I really need to get down to the basics, understanding the fundamentals.

At least I have a big interest in this stuff so sticking with it shouldn't be a problem. That's at least part of the battle, I'm sure. Tell you what: when I'm published in Nature, I'll post the link in this thread. Then, you'll all finally know what is dark energy, what happened before the Big Bang and why we Liverpool supporters are destined to remain in endless premiershipless sorrow. :P

Sean
"... quit trying to upset and disturb Dr. Venkman..."
Last edit: 9 years 11 months ago by RandomPillars.
9 years 11 months ago #95385

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