The Universe

[Hedgecutter]

 

I toured the great ocean road in Oz a couple of times and honestly couldn't believe how many stars you could see cos you're miles away from any major light sources.

I had a similar thing out in the arse end of Kenya. Mental.

[Ziggy]

Has anyone ever been to a proper dark sky location? I've wondered for years what you can actually see. There are loads of google images but i suspect they have been doctored or filtered or some-such. Coming back to Oban from Colonsay on the night sailing you get a really good view (shooting stars, the milky way from the corner of your eye etc) but can you really see stuff like in the video below from earth with the naked eye?

http://vimeo.com/75542539

Great thread btw

My Mother in Law used to stay in Chile and on one visit we went to one of the observatories up in the Andes.

It was brilliant looking through the telescopes but the best bit was just looking up with the naked eye. It was awesome.

[MONKMAN]

I toured the great ocean road in Oz a couple of times and honestly couldn't believe how many stars you could see cos you're miles away from any major light sources.

Fraser Island in oz was the clearest sky I've ever seen. The views of the stars were unreal.

[jock001]

I had a similar thing out in the arse end of Kenya. Mental.

Fraser Island in oz was the clearest sky I've ever seen. The views of the stars were unreal.

I guess the best place must be slap bang in the middle of the pacific but anywhere there isn't much light is so different to what I'm used to it's amazing.

[Raidernation]

It was pretty dark in Salen, Ardnamurchan when I lived there. No light source at all near my house.

[Confidemus]

My Mother in Law used to stay in Chile

I'm willing to bet that's the first time that collection of words has been used in that particular order in the history of P&B.

[welshbairn]

Just had a thought:

Some time ago Hawking wrote a paper that started a controversy that has lasted until the present day. In the paper he pointed out that if there were an event horizon, the outgoing state would be mixed. If the black hole evaporated completely without leaving a remnant, as most people believe and would be required by CPT, one would have a transition from an initial pure state to a mixed final state and a loss of unitarity. On the other hand, the ADS-CFT correspondence indicates that the evaporating black hole is dual to a unitary conformal field theory on the boundary of ADS. This is the information paradox.

Recently there has been renewed interest in the information paradox. It was suggested that the most conservative resolution of the information paradox would be that an infalling observer would encounter a firewall of outgoing radiation at the horizon. There are several objections to the firewall proposal. First, if the firewall were located at the event horizon, the position of the event horizon is not locally determined but is a function of the future of the spacetime.

Another objection is that calculations of the regularized energy momentum tensor of matter fields are regular on the extended Schwarzschild background in the Hartle-Hawking state. The outgoing radiating Unruh state differs from the Hartle-Hawking state in that it has no incoming radiation at infinity. To get the energy momentum tensor in the Unruh state one therefore has to subtract the energy momentum tensor of the ingoing radiation from the energy momentum in the Hartle-Hawking state. The energy momentum tensor of the ingoing radiation is singular on the past horizon but is regular on the future horizon. Thus the energy momentum tensor is regular on the horizon in the Unruh state. So no firewalls.

For a third objection to firewalls I shall assume that if firewalls form around black holes in asymptotically flat space, then they should also form around black holes in asymptotically anti deSitter space for very small lambda. One would expect that quantum gravity should be CPT invariant. Consider a gedanken experiment in which Lorentzian asymptotically anti deSitter space has matter fields excited in certain modes. This is like the old discussions of a black hole in a box. Non-linearities in the coupled matter and gravitational field equations will lead to the formation of a black hole. If the mass of the asymptotically anti deSitter space is above the Hawking-Page mass, a black hole with radiation will be the most common configuration. If the space is below that mass the most likely configuration is pure radiation.

Whether or not the mass of the anti deSitter space is above the Hawking-Page mass the space will occasionally change to the other configuration, that is the black hole above the Hawking-Page mass will occasionally evaporate to pure radiation, or pure radiation will condense into a black hole. By CPT the time reverse will be the CP conjugate. This shows that, in this situation, the evaporation of a black hole is the time reverse of its formation (modulo CP), though the conventional descriptions are very different. Thus if one assume quantum gravity is CPT invariant, one rules out remnants, event horizons, and firewalls.

Further evidence against firewalls comes from considering asymptotically anti deSitter to the metrics that fit in an S1 cross S2 boundary at infinity. There are two such metrics: pe- riodically identified anti deSitter space, and Schwarzschild anti deSitter. Only periodically identified anti deSitter space contributes to the boundary to boundary correlation func- tions because the correlation functions from the Schwarzschild anti deSitter metric decay exponentially with real time. I take this as indicating that the topologically trivial periodically identified anti deSitter metric is the metric that interpolates between collapse to a black hole and evaporation. There would be no event horizons and no firewalls.

The absence of event horizons mean that there are no black holes - in the sense of regimes from which light can’t escape to infinity. There are however apparent horizons which persist for a period of time. This suggests that black holes should be redefined as metastable bound states of the gravitational field. It will also mean that the CFT on the boundary of anti deSitter space will be dual to the whole anti deSitter space, and not merely the region outside the horizon.

The no hair theorems imply that in a gravitational collapse the space outside the event horizon will approach the metric of a Kerr solution. However inside the event horizon, the metric and matter fields will be classically chaotic. It is the approximation of this chaotic metric by a smooth Kerr metric that is responsible for the information loss in gravitational collapse. The chaotic collapsed object will radiate deterministically but chaotically. It will be like weather forecasting on Earth. That is unitary, but chaotic, so there is effective information loss. One can’t predict the weather more than a few days in advance.

Could be wrong..

[dorlomin]

Just had a thought:

Some time ago Hawking wrote a paper that started a controversy that has lasted until the present day. In the paper he pointed out that if there were an event horizon, the outgoing state would be mixed. If the black hole evaporated completely without leaving a remnant, as most people believe and would be required by CPT, one would have a transition from an initial pure state to a mixed final state and a loss of unitarity. On the other hand, the ADS-CFT correspondence indicates that the evaporating black hole is dual to a unitary conformal field theory on the boundary of ADS. This is the information paradox.

Could be wrong..

Word for word from here.

[Hedgecutter]

can’t predict the weather more than a few days in advance.

Could be wrong..

The other day Carol Kirkwood was telling me that it had was pouring down in Aberdeen despite it being lovely and sunny.m To be fair to her, it chucked it down a couple of hours later. Basically, sometimes they can't predict the weather at the time.

The forecast is all model driven anyway. The modern maps on TV can show Cowdenbeath and Kelty being wet with the rest of Fife dry in two days time but it's probably just all stochastic randomness which the computer's churned out based on a few data points. Always going to be wrong, just a question of by just how much.

[LongTimeLurker]

Word for word from here.

You even had to check? Next up will be 8MileBU's theory of relativity. If you fling a boomerang-shaped piece of shite towards Linlithgow at the speed of light it will have travelled through time as well space by the time it arcs back to Bo'ness providing the time required to step out of the way so it winds up hitting somebody in Grangemouth.

[KeeperDee]

You even had to check? Next up will be 8MileBU's theory of relativity. If you fling a boomerang-shaped piece of shite towards Linlithgow at the speed of light it will have travelled through time as well space by the time it arcs back to Bo'ness providing the time required to step out of the way so it winds up hitting somebody in Grangemouth.

Near enough spat my water on the laptop screen. Bravo.

[AberdeenBud]

Just ordered a new fairly cheap scope, anyone recommend any app's/websites that can help a virgin gazer like myself?

Thanks in advance.

[cracowjambo]

How man solar systems are in the galaxy?

[cracowjambo]

How many solar systems are in the galaxy?

[Granny Danger]

How man solar systems are in the galaxy?

14.

[cracowjambo]

14.

If it's 4.5 lightyears to the nearest does that mean aliens can travel faster than light or are the just near by?

[KeeperDee]

If it's 4.5 lightyears to the nearest does that mean aliens can travel faster than light or are the just near by?

Maybe they're already here.

[Granny Danger]

If it's 4.5 lightyears to the nearest does that mean aliens can travel faster than light or are the just near by?

They can travel faster than light. Their technology is far more advanced than ours.

[dorlomin]

Just ordered a new fairly cheap scope, anyone recommend any app's/websites that can help a virgin gazer like myself?

Thanks in advance.

Stellarium is very popular, free and I like it.

There is currently an active course on Coursera that is aimed at acting as an introduction to astronomy to uni undergrads, the first set of lectures covers 'positional astronomy' which is how the astronomers work out where things are in the sky. Might be too advanced for what you are looking for but you it could be worth downloading the first 3 lectures on week 1 for getting yourself into it a bit deeper than just recognising constellations.

[mikebhoy123]

Stellarium is very popular, free and I like it.

There is currently an active course on Coursera that is aimed at acting as an introduction to astronomy to uni undergrads, the first set of lectures covers 'positional astronomy' which is how the astronomers work out where things are in the sky. Might be too advanced for what you are looking for but you it could be worth downloading the first 3 lectures on week 1 for getting yourself into it a bit deeper than just recognising constellations.

No, I can't recommend anything - all I can say is good luck mate and if you get any bother, If you contact me - I will be more than happy to try and help....

I'm interested in astronomy and my GF bought me a decent telescope ( must have cost a good few hundred £ ) but it came with no instructions and I could never get it to focus properly... Honestly, I worked as a Field Service Engineer on LASER equipment for 3 years ( about 10 years ago ) so I know how to align optics / mirrors but I could never get the fucker to work.... It got " accidentally " thrown out when I moved house - which I regret so happy to help when you face the inevitable problems of getting the fekin thing to work....