Royston

I realize this is an old thread, and three pages long, (so sorry if this has already been covered) but there's only a paradox if you ignore one of the main tenets of general relativity i.e coordinates do not have an immediate metrical significance.

IOW, there is nothing physical about a coordinate singularity, which is what you get for a stationery observer, who's radial distance is [math]O_d>>R_s[/math]. Where [math]R_s[/math] is the Schwarzschild radius. A transformation of coordinates can eliminate infinite redshift et.c. I think confusion arises when special relativity is applied to general relativistic situations, there's bound to be inconsistencies as SR doesn't cope with gravity.

I'm currently bogged down with three assignments (two on extreme environment astrophysics, the other is more basic astronomy), I need to cram two weeks work into one, as I'm off on holiday next week.

Incidentally, the comic strip in the OP seems particularly apt. I went to vote today (election day in the UK) and after cramming my brain with the physics of accretion discs, I found great difficulty putting some paper into a slot. I was told to fold it twice

EDIT: Good luck ajb

And if marijuana didn't exist, do we really believe the heavier drugs would be an esoteric indulgence? Somehow without this magical "gateway" drug, access to the heavy stuff is occluded? I guess I just don't understand the significance of pointing out marijuana as a starting point. The subtending logic implied by that notice just doesn't check out.

I would imagine people who experiment with so-called hard drugs, are predisposed to experiment, it's just cannabis is more readily available, and is considered softer, so it stands to reason this will be the first drug they try.

I agree with Padren, in that some people who supply cannabis, also supply other drugs, if the customer fancies a change, (or even talked into it) it's available, and this could be another reason for this 'gateway' label.

As for stats, well they're a bit sketchy (but better than a survey of anecdotes.) There is a difficulty in getting the data, which is explained near the beginning, and although this article is talking about drug problems, the same difficulty extends to people who use drugs, and don't have any problems i.e getting stats on the number of cannabis users, or amphetamine users for example.

http://www.drugscope.org.uk/resources/faqs/faqpages/how-many-people-are-addicted

While the data on new notifications helps track how many people are newly seeking help for their drug use, it does not indicate how many people are addicted or having problems with drugs in total. To find this we have to find out firstly how many people are in treatment as a whole and then how many people are having drug-related problems but not seeking help.

However, cannabis does seem to be a lot more popular, and figures for people with problems is really quite low, so it appears that many are using cannabis but not experimenting with harder substances.

I realise this is an old thread, but thought some of you may be interested, I'll post more updates as and when they happen...

Tomorrow morning the appeal judgment in Simon Singh’s case with the British Chiropractic Association will be handed down at the Royal Courts of Justice. It is going to be a very important day for us as this judgment will have implications beyond Simon’s case on science writing and on libel law reform.

 

The judgement, written by three of the most senior judges in England and Wales - Lord Chief Justice Lord Judge, Master of the Rolls Lord Neuberger and Lord Justice Sedley - is on Simon's appeal against the preliminary ruling on meaning given by Mr Justice Eady in May 2009. It will determine whether Simon can defend his writing as fair comment or will have to justify it as fact.

 

Please do come to Court 4 at the Royal Courts of Justice, Strand, London tomorrow, Thursday 1st April, at 9.30 am to hear the result and show Simon your support.

 

Simon was interviewed about his case and the wider campaign for The Times on Saturday. Read it here: http://business.timesonline.co.uk/tol/business/law/article7078008.ece#cid

 

For a round up of the case so far, and possible implications of the judgement, see Jack of Kent’s blog here: http://jackofkent.blogspot.com/2010/03/simons-judgment-day.html

Merged post follows:

I'll post more updates as and when they happen...

I didn't mean to sound like a TV news ad

Good news though...

A very quick note to make sure you heard that Simon Singh’s appeal in his case with the BCA was upheld today. It means that Simon can now defend his article as comment rather than as fact, as Justice Eady had originally ruled.

 

Simon said today: “It is ridiculous that it has cost £200,000 to establish the meaning of a handful of words. I am delighted that my meaning has been vindicated by three of the most powerful judges in the country, and I relish the opportunity to defend this meaning in court. However, I am still angry that libel is so horrendously expensive. That is just one of the reasons why the battle for libel reform must continue.”

 

You can read more comments from campaigners and supporters at www.libelreform.org/news/450-judgement-in-simon-singh-libel-case

 

And the judgment and Simon’s lawyer’s notes on what this means for Simon’s case and for libel reform is here: http://www.senseaboutscience.org.uk/index.php/site/project/473/

 

Jack of Kent has blogged on the ruling here: http://jackofkent.blogspot.com/

 

The Guardian http://www.guardian.co.uk/uk/2010/apr/01/simon-singh-wins-libel-court

 

The Daily Telegraph http://www.telegraph.co.uk/news/uknews/7543685/Science-writer-Simon-Singh-wins-Court-of-Appeal-libel-battle.html

 

BBC Radio 4 World at One http://www.bbc.co.uk/programmes/b00rlff7

 

BBC online http://news.bbc.co.uk/1/hi/uk/8598472.stm

 

And check here for updated lists of press coverage: www.senseaboutscience.org.uk/index.php/site/project/473/

 

Keep an eye out for Simon, his lawyer Robert Dougans and members of the libel reform campaign on Channel 4 news, the BBC News channel, Sky News and BBC radio stations this evening.

Simon, and the campaign for libel reform, both still have a very long fight ahead of us. We are very pleased the three most powerful members of the Judiciary in England have recognised the need for libel law reform. We need to make sure everyone else does too.

There's no spacetime beyond the event horizon using an unmodified Schwarzschild metric, there is if you use advanced Eddington-Finkelstein coordinates, where the t and r (distance) coordinates are related by...

[math]ct'=ct+R_sln\left(\frac{r}{R_s}-1\right)[/math]

You're talking about a coordinate singularity, which is what the paper you cited is discussing, (which is flawed reasoning to your argument) in a limited way, what you said is right i.e 'there is no spacetime inside the event horizon', but only when using an unmodified Schwarzschild metric, and that's because it's ill equipped to deal with events at and past the event horizon...time like, becomes space like.

Isn't a black hole considered to be everything inside it's event horizon?

Yeah, it's just the region bounded by the event horizon.

In reality, don't all black holes spin?

Kerr black holes i.e mass and angular momentum (spin if you like), are the most likely, but that's not really relevant to the thread.

IIRC the volume that's bounded by the event horizon, is just the surface area multiplied by ct, where t is the longevity of the black hole, so...

[math]V_{bh}=4\pi r^2 ct[/math]

Though we still have the problem of [math]V_{bh}\rightarrow\infty[/math]

I actually lost sleep thinking about this last night, and wrote a lengthy reply earlier, and then decided to ditch it, so I may come back to this, here's a short version...

I wondered if there was a way around [math]V_{bh}\rightarrow\infty[/math] using Kruskal coordinates, which copes with the problem of asymmetry using advanced Eddington-Finkelstein coordinates i.e the modified Schwarzschild solution.

In principle, the point where a photon gets expelled (in the other domain), could be a cut off point for the volume, i.e there should be a change in curvature of the outgoing null geodesic (from a straight world line, to one curving outwards.) Although Kruskal coordiantes do away with coordinate singularities, AFAIK there's still a gravitational singularity to worry about, so I'm a bit confused on how this works.

However, perhaps an expert could point out the flaw in this, or if it doesn't quite make sense et.c

EDIT: Congrats on the promotion to mod Mr. Skeptic

Oh look, the "What don't you like about SFN" thread has gone over 100 posts.

I spotted this earlier, which seemed quite apt...

I don't understand your argument DH, I didn't mention the use of the word 'dark', and confirmation that dark energy is a real effect (in your words) is exactly that, it's been confirmed.

I thought the article was interesting because of the methods used to conclude the fact of accelerated expansion...so I thought the title was appropriate i.e the measurement of expansion is a lot more refined than it was when it was first discovered, so surely it's a genuine addition to the Einstein equations ?

I can’t use to the general relativity.

I suggest you do, you can derive the Newtonian limit via the Ricci tensor, it should reduce to Poisson's equation, from there you have gravitational potential.

So (unless I'm missing something) your derivation is somewhat back to front, you certainly can't derive any constants (e.g cosmological) via Newtonian methods. You need the assumptions of SR and GR.

EDIT: I'm a GR newb, so someone correct me if the above, isn't quite right.

I've always liked the idea of having a tail for some reason...and wings, as shakes has already mentioned. I have an issue with population, so any health benefits e.g limb regeneration like an axolotl, is a no no for me.

Another aesthetic change, is that people are born with random coloured skin, and certain attributes, e.g bone structure (to an extent) et.c so the whole idea of race is obliterated.

In short, I want to be a flying purple, greater spotted, monkey man.

This was posted by my tutor on our Uni forums, thought some of you may be interested....

http://www.spacetelescope.org/news/html/heic1005.html

From the article...

A new study led by European scientists presents the most comprehensive analysis of data from the most ambitious survey ever undertaken by the NASA/ESA Hubble Space Telescope. These researchers have, for the first time ever, used Hubble data to probe the effects of the natural gravitational "weak lenses" in space and characterise the expansion of the Universe.

"Dark energy affects our measurements for two reasons. First, when it is present, galaxy clusters grow more slowly, and secondly, it changes the way the Universe expands, leading to more distant — and more efficiently lensed — galaxies. Our analysis is sensitive to both effects,"

Gravitational waves are certainly not derived from SR, the simple reason being, that SR is not a theory of gravity. For the equivalence principle to hold, spacetime needs to be curved aka a relativistic theory of gravity.

Waves are produced via accelerated bodies in a curved spacetime. That's the raw basics, I, or someone with more expertise can go into more detail if you want.

EDIT: Oops, ajb beat me to it.

Of course Cap'n is fully responsible for the below...

The fever left her, and she served

She deserved

Now the men observed

The curved

He said as he stroked Howard's face"

 

The fire of God came again to

John's cock continued to spew

Behold, the spew

body, has the same object in view

the balls swelling to match the hue

Ulysses ryhmescheme, with the brains; bebsw

I agree with the second bullet point, in that all physics is theoretical (but that extends to every other branch of science.) I've never really given it much thought, to the meaning of the term.

I've always stuck it in the category of 'what is yet to be tested', but that doesn't make sense with afterthought...I guess it's indicative about the perception of physics more than anything else, that such a category should exist, i.e over theoretical biology et.c

Crysis 2? It isn't out yet, is it?

Oops...this year, I meant Crysis Warhead.

Leader Bee is right, Crysis / Crysis 2 is still the benchmark, because the Crytek engine is still the most background heavy graphics engine to date, despite it's age.

I was looking for other things in my test, which I simply can't be bothered to explain right now.

In general there will be off-diagonal terms and every term can depend on all the coordinates.

Thanks ajb, this was what (in a clumsy way) I was alluding to...however, I'm having a real hard time trying to visualize what's going on, I guess I'm not content with just method.

In any case, I'll post the results of the connection coefficients, and geodesics et.c tomorrow, it's good practice to tackle stuff outside the scope of what you're being taught...at least I think so.

1 and 2, amount to the same thing don't they ?

I think the third is asking for trouble personally. I'd go for the first or second option (it doesn't matter which), ftl communication / travel, would manifest itself in technologies that would benefit us way beyond anything we use right now.

However, it depends what point in history you're referring to jryan...or is that a free choice ?

I think you worded your question very poorly.

By the time I got to answer the question, I was practically asleep, so sorry about that.

Your question is if the gXX term will always depend on at most as many variables as the gYY term for Y>X? The answer would be "no": Just switch the names of x1 and x2 which is nothing but a renaming but will also swap g22 and g33. You can also have non-zero diagonal terms in general.

Thanks, that's precisely what I was getting at, I just havn't come across an example yet (in my course) where the names of x, were switched, but that makes things a lot clearer.

Does it let you continue your game to play side missions after the main quests or do you have to start the game over like in the first one?

You have to start the game over.

The engine is Dunia I believe..

I just double checked, and you're right, albeit it's a heavily modified version of the Dunia engine.

Well being a GR course, Einstein notation is used extensively, so I'm probably missing something obvious...or I worded my question poorly.

Are my steps correct so far ? If so, then I know I'm on the right track at least.

I've just finished playing Mass Effect 2, which I had to wait a month for, because the order was screwed up. It was good while it lasted, well written et.c but seemed to be over really quickly (I blame the structure of the missions / story for that.)

I'm sure the game relies on replay value, you get extra perks when playing through again, but I see that as more of a chore than anything.

I've also been playing the excruciatingly poor Avatar game, which I downloaded solely as a graphics test for SLI. It uses a modified engine from Far Cry 2 (I forget the name), and does look incredible on my set up...the game itself, is dire.

I've also had a few games on Civilization IV recently, where I believe Civilization V is due out soon...so something to look forward to.

This is isn't homework, just something I decided to have a crack at, alongside my current course, and forgot about it. Just need confirmation on the last step.

I wanted to find the connection coefficients of a hypersphere, so the line element is...

[math]dl^2=R^2[d\psi^2+sin^2\psi(d\theta^2 + sin^2\theta d\phi^2)][/math] so...

[math]dl^2=R^2d\psi^2+R^2sin^2\psi d\theta^2+R^2sin^2\psi sin^2\theta d\phi^2[/math]

Where...

[math]x^1=\psi[/math]

[math]x^2=\theta[/math]

[math]x^3=\phi[/math]

So the metric is...

[math]g_{ij} = \left[ \begin{array}{ccc} R^2 & 0 & 0 \\ 0 & R^2sin^2 (x^1) & 0 \\ 0 & 0 & R^2sin^2(x^1)sin^2(x^2) \end{array} \right][/math]

Where the dual metric [math]g^{ij}[/math], is the inverse matrix of the above.

Now this was the bit I was unsure about...

[math]\frac{\partial g_{22}}{\partial x^1}=2R^2sin(x^1)cos(x^1)[/math]

[math]\frac{\partial g_{33}}{\partial x^1}=2R^2sin(x^1)cos(x^1)sin^2(x^2)[/math]

[math]\frac{\partial g_{33}}{\partial x^2}=2R^2sin^2(x^1)cos(x^2)sin(x^2)[/math]

[math]\frac{\partial g_{ij}}{\partial x^k}=0[/math] for all other values of i,j,k.

Now is it a general rule to partially differentiate each [math]x^k[/math] term, for increasing values of k (see the second to last equation for example). I'm guessing it is, because these will crop up in the connection coefficent equations, and determine which ones are independent, and non zero et.c...I just wanted to be doubly sure.

BTW, it's coming up to 2am where I am, so I might be being a bit dumb here.

It's a personal preference.

Which I respect, I was merely questioning the motivation of delaying sex, i.e encounters later on in life, will overshadow any teenage fumblings. Perhaps I should of emphasized 'side note' at the beginning of my post, as I was specifically speaking of this 'first time.' Don't get me wrong, I'm not saying anyone should rush in (there's no reason to), but...

this issue is more about the romantic chick-flick movies out there speaking of this magical love bond that makes first-time-sex this awesomely amazing feat.

...amongst a plethora of other misguided reasons why such a thing should be delayed.

If you don't feel comfortable, don't do it.

Well, it's highly unlikely anyone will feel comfortable doing something for the first time, especially if it's surrounded by some social stigma. Perhaps I'm being a typical 'bloke' about this subject, and as much as I recognise levels of intimacy, that doesn't mean I find certain hang ups, as a little daft. But as you said, it's personal preference.

Why are alternate formalisms to physical phenomena altogether bad?

There's nothing wrong with an alternative formalism, providing it makes predictions of physical phenomena, and improves on the original. IOW if it aint broke, don't fix it.

For instance I don't know how to model energy, or energetic interactions. Could you use just a graph really.

Well a graph is mathematical. However, if you do plot a bunch of data, and find a trend or pattern, a mathematical model that predicts that behaviour would surely be more beneficial i.e I plug a value in, and get a result...but surely that's what you'd be striving for, once you've gathered your data.

It might help, if you gave more solid examples.