imatfaal

I've said it before and I will say it again - I like the strict no nonsense way this forum is run (and your moderation is a significant part of that ethos). There are a good couple of dozen posters who are clearly highly knowledgeable and willing to teach/discuss/chat, and that is an invaluable resource; I am convinced that a good number of those posters would not be so forthcoming if they were constantly needing to fend off attacks from crackpots, moody teens, and single-issue fanatics.

Slinkey - quite apart from Migl's arguments that I need to think over - this section of your argument I think has a lot of problems

Indeed. But here's the point - science is about observation. Thus if we do not see something enter a BH then nothing has entered the BH. When science leaves the realm of observation we enter a grey area of postulates that we cannot prove in any way shape or form except maybe in mathematics which (according to Godel) cannot be self-consistent.

You are making the incorrect assumption that for an observation to be valid it must be able to be made from all frames of reference - the whole concept of SR, lightcones, simultaneity etc showed this to be false. This is a hangover from newtonian physics; the reality of Bob's observations from an accelerated reference frame do not compromise the reality of Alice's observations from the free-falling reference frame. I don't believe you are questioning the nature of blackholes - it is just a lack of engagement with altered frames of reference

This question is definitely doing the rounds of the physics teachers of world - I have seen it crop up several times recently. It seems a difficult one - because whilst none of the posts I have seen have had trouble working out the speed of contact with the ground many posters haven't made the link to carry on. And there is an implicit assumption that must be made that I think makes the question a little dodgy; unless it is that assumption that the questioner is looking to teach.

I will read back the thread if I can find time for 6 pages - and from your summary its tough stuff

I must admit I find myself at odds with your very opening; nothing can enter =/= nothing can be seen to enter

The original premise was that black holes cannot be entered; specifically, that nothing can be seen to cross the event horizon (for the purposes of this thought experiment we were ignoring gravitational redshifting and tidal forces) by an outside observer due to the time dilation when an infalling object nears the event horizon.

The fact that Bob in an accelerated exterior reference frame sees nothing cross the event horizon does not mean that nothing can enter a black; all it means is that nothing can be seen from that frame to enter a black hole. Alice in freefall enters the blackhole from her reference frame; Bob sees this in slower and slower motion, dimmer and redder due to the gravity of the blackhole. In the classical two diamond space time diagram of a simple blackhole whilst Bob follows a hyperbolic fixed radius line Alice follows a straight line; Bob never sees Alice cross not because she doesn't but because he is in a different reference frame and no 45deg light-like signal from Alice can ever intersect with Bobs space time line that is asymptotic to the 45deg light-like line.

But I will read the thread to see how you have dealt/argued with this. I will also dig out a diagram to better explain the above paragraph.

For that to be true civil wars/revolutions cannot be considered wars. That's a bunch of hooligans trying to overthrow a government, who could be seized and brought to trial.

And if they fail, they almost certainly will be brought to trial (although possible not a very fair one - perhaps only a military tribunal in a deniable off-shore location).

And what are the chances that one of us is actually a computer AI participating in a long-term Turing Test? I bet it's...um...Me. Oh Bugger! What a giveaway; failed again!

Chris

There is a great calculator here A black hole of 4*10^6 solar masses (similar to that at centre of milky way) has a Hawking Radiation temperature of around 10^-14 Kelvin.

Alan

It would also mean that cosmic background radiation for a given place is constant throughout all of time or at least that the amount the black hole is being fed is always enough to prevent it from evaporating entirely.

I havent read through the thread but to make it clear - if the background temp is higher than the temp of the black hole the blackhole not only doesnt evaporate, it increases in mass; this increase in mass causes its temperature to DROP, which in turn causes it to gain even more mass (ie slight positive feedback). The same applies when the blackhole temperature goes above background, it loses mass which causes it to gain temperature, which in turn increases the rate of evaporation. ie it will not reach an equilibrium, it will either get bigger or smaller.

then it brings me back to my earlier point about ever reaching the surface of a black hole if you fall into it.

I haven't read what went before - but whilst a distant observer in an accelerating frame will never see the poor guy fall through an event horizon - from the frame of the victim there is no change and no noticeable affect of the event horizon. Poor old victim will sail straight through and get ripped up by the tidal gravitational forces

I would define the floor as what I walk upon - so perhaps not. But you can potentially walk normally on the inside surface of the outer rim - and you can call that what you will.

If spining produces gravity, can a person walk on the ceiing of a space station?

Thats why the sci-fi films have the space stations of the future as enormous doughnut shapes. If the doughnut is spinning, in the rim you would feel as if there was gravity towards the outer edge - at the hub one would be weightless.

I am convinced that any decent amount of postgraduate research changes ones attitude to the material and breaks a vital bond with the undergrad learner; which is why senior year undergrads can connect and teach in a different and complementary manner to postgrads (from full tenured profs to phd candidates). There is something in the depth, the different weighting given to information and the new ability to be sceptical that creates a marked change; it's liberating but also quite scary when you realise that there is no real authority in the area you are studying. I cannot help but think that the process of teaching lower year students is also a great experience for the undergrad teachers - there is no better way of organising your thoughts than having to prepare to teach them.

When the size of the animal starts to approximate the size of the habitat then Antoine might have had a point but even with the most terrible of lizards that is not even close. The change in mass between the dinosaurs and creatures today is miniscule when compared to the mass of the earth; the difference between a 11000kg of a Bull Elephant and 60000kg of a Brachiosaurus is unimportant in the context of a 5 million million million million kg earth. And even though it is in the sea the largest animal ever known is still around today.

I realise that different jurisdictions have different laws - but in UK I think Captain Refs actions could well still be considered illegal. A defence to murder that the action was justified requires a reasonable subjective belief that these actions were necessary and proportionate - ie even if the man on the clapham omnibus thinks you were justified; if the accused admits to believing he used excessive force then the defence fails. And, of course, if you had admitted to shooting at random then you would have no claim to a reasonable belief. You would have the mens, the actus, no justification and no excuse. I would have to double check this - but that's the way I think it goes.

I'm not accusing you of doing what I described, just pointing out that the "do you have any evidence?" question often does not stop people.

Whoops, I misunderstood - OK reread post and understand yours now.

Captain

Just noticed your post on the rep points above - Wow, nice one! Talk about the benefits of an efficient and benevolent dictatorship

I have noticed a striking tendency for members to draw conclusions about others with little evidence. For example, while debating another member it's common to conclude they must intentionally be using deceptive debate tactics, or that their logical fallacies are introduced as intentional red herrings, or that a pattern of reported posts is evidence of intentional subversion. Generally I find it safer to assume that your opponents faults are a result of their faultiness, rather than malice.

Captain - not sure why you have singled out one sentence of my post - and responded as above. I do follow who says what and respond to the person with all the corresponding thoughts of what he or she has posted in the past. I do not think Marat is the sort of poster who says much by mistake or 'faultiness' (I like that word).

As Marat posted the below immediately after one of the (admittedly few) posts with a photograph:

Since we don't know who is behind any of these purely symbolic name tags, which could very well represent entire committees of people writing under a single nom de plume, I don't find it sensible to be voting for these names as though they were people.

I thought it was fairly reasonable to ascertain on what basis he made that comment.

Marat - that's a very strange quasi-solipsistic view to take and would seem to mechanize and dehumanize what is basically a social interaction. Whilst many things are possible, few are likely and to live one's life betting on the least likely option seems perverse. Do you have any evidence that the man staring out from the post above yours isn't an individual but a committee?

On the friendliness of this site - I could not disagree with you more. This is a noticeably strict site, where the mods are pretty punctilious, potentially draconian, but there is very little flaming, sledging or rudeness.

Happy Birthday!

Back on the rep points - would it not be possible to allow member to give only +ve rep points until they have posted 30 or so messages? This would seem to weed out lots of the neg reps from disgruntled teens who have their pet theory torn to shreds.

edit fr double post

Will re-iterate what Bignose said - but from different angle, I am established with a good long term job etc etc but still suffer from the bad credit rating I built up many years ago at University. Its pretty hard to build up a good rating - it is damn near impossible to expunge a bad one. In England it is the bizarre situation that if I had been convicted of a minor criminal offence my record would have been wiped clean by now, but as I had a county court judgment against me for unpaid poll tax and the bailiffs came round I still suffer because of it. Be more careful to avoid bad credit rating than building up a good one.

Kids who think rebellion is the automatic gainsaying and mockery of anything said/stated by any authority figure (or in SF.N's case - vague approximation of an authority figure).

The only time I will neg-rep is when the poster is rude/obnoxious; or, no-matter how politely, answers a straight science question with a wild guess dressed up as fact.

Yep - the forum had a pet flat fish - and that sole was sold to a group of nutty l ron hubbard freaks on April 1st

I think perhaps you are thinking of scribes or bards.

No I am thinking of Daidoji Yuzan's instructions to wannabe Samurai to avoid being merely a rustic warrior and take up poetry, calligraphy and the tea-ceremony.

Apparently there are some problems with Romanov's initial claim.

 

http://www.computer....solution-flawed

Thanks.

Well...

 

I wouldn't say a samurai was heavily armoured, for one, Japanese steel at the time of the samurai ~ 1100 to 1600 AD was of inferior quality and hard to come by compared to steel of western europe. In this scenario i'd go with the samurai anyway as ninjas are indeed geared towards infiltration, assasination and spying and not all out warfare.

 

A matchup i'd really like to see is a Samurai vs the same time period equivilent from western Europe. Lets see just how those magical/Legendary and able cut through concrete Katanas are against full plate armour.

Too right! We might see how much the ability to craft a fine poem, or a knowledge of calligraphy really helps a fighting man.

Because quite a lot of Pakistanis did not support Osama Bin Ladin and hated the fact that their intelligence/security forces seemed to enjoy playing the dangerous game of soft-peddling on the extremist terrorists with Pakistan. There are far too many Pakistani military/security personnel who see the only enemy as India - and everybody else as a potential asset to be utilised. Pakistan has a population the same magnitude as the United States - and to expect unanimity amongst them would be naive; the islamic extremist hate the government due to the ties with the united states anyway...

And I have just remembered this is a conspiracy theory thread and you weren't serious any way