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Physics, Astronomy & Cosmology / Why the discrepancy between orbital velocity and photon sphere radius?

« on: 12/09/2010 12:44:30 »

The formula for an approximation of orbital velocity around a mass M (where the mass of the orbiting 'body' is negligible) is:

   

ref: http://en.wikipedia.org/wiki/Orbital_velocity

...and the formula for the Photon Sphere radius is:

   

ref: http://en.wikipedia.org/wiki/Photon_sphere

...and finally, the formula for the Schwarzchild Radius (of a non-rotating BH) is:

   

ref: http://en.wikipedia.org/wiki/Schwarzschild_radius

Where (using mks units):

  G = the Gravitational constant = 6.674 x 10^-11
  M/m = the mass of the orbited body (we'll use the mass of the Earth here, just for fun) = 5.9736 × 10²⁴
  c = the speed of light = 299792458

Using these values, the Schwarzchild Radius for an Earth sized BH is: 0.0088718 (m) i.e. a little under 9 mm

...and using this as the radius to find the orbital velocity we get 211985280 (m/s), which is < 'c'

However, the radius of the Photon sphere, where the orbital velocity must be 'c', turns out to be: 0.01330768 (m), which is well outside the Schwarzchild radius.

So can anyone explain why a negligible mass object orbiting a BH just outside its event horizon will be travelling more slowly than the light in the Photon Sphere, which is orbiting it quite a bit further away?

2

Just Chat! / What's cooking tonight?

« on: 08/09/2010 22:07:24 »

Just a quick thread for people to post what they're cooking (not just eating, so please don't post about McDs etc.)

I've currently got a sweet & sour sausage casserole bubbling away in my slow-cooker.  Smells good, so far  [], and I'll be eating it whatever it actually tastes like (because I hate throwing food away).

Proof of the err... casserole... to follow...

3

Just Chat! / Something for the sheep fanciers amongst us

« on: 01/08/2010 12:52:05 »

Those sheep botherers fanciers amongst us might like to visit my home town...

http://news.bbc.co.uk/local/essex/hi/people_and_places/arts_and_culture/newsid_8857000/8857730.stm

I'll try to get some pics of some them in situ this afternoon.

4

Geology, Palaeontology & Archaeology / Does anyone know anything about these two craters in Mongolia?

« on: 15/03/2010 18:08:20 »

I spotted these two craters while browsing in GoogleEarth but I've been unable to find out anything about them.  They're located in Nei Mongol and the closest large settlement I can find seems to be Xilin Gol.  There are known volcanic features in this region but they seem to be quite someway from these structures.  Similarly, there is a known, but much smaller impact crater, Tabun-Khara-Obo, about 366 km to the west.

Google Maps (see below) shows a label "Huarggen Tala" beside the larger of the two structures but I get no hits from this in a Google search.  Note that if you look at them in GoogleMaps Terrain view, the smaller northern structure appears to have a clearly defined central peak, typical of impact craters, whereas the larger southern structure is much less clearly defined.

http://maps.google.co.uk/?ie=UTF8&ll=44.198944,114.248199&spn=0.43123,0.752563&t=h&z=11

Unfortunately, we can't upload .kmz attachments for GoogleEarth, but the co-ordinates are  44°13'47.64"N 114°14'8.52"E

Updated:  Looking a little further to the East, I just noticed these three structures too:

http://maps.google.co.uk/?ie=UTF8&t=h&ll=44.342512,114.903259&spn=0.215089,0.376282&z=12

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Just Chat! / Amusing examples of recursion

« on: 01/03/2010 12:42:21 »

Just a few examples to kick things off:

Computer geeks will have heard of the GNU project (for 'linux' is really just the name of the kernel).  GNU is, of course, an acronym for 'GNU's Not Unix'

Then there's the old song "There's a Hole in My Bucket", as recorded by Harry Belafonte and Odetta in 1961.

see: http://en.wikipedia.org/wiki/There's_a_Hole_in_My_Bucket

Another example: Most people will have also noticed that when doing a Google search the results page will also often include a link saying "Did you mean: ..." if there was any ambiguity in the original search terms.  However, do a Google search on "recursion" and this prompt will ask: "Did you mean: recursion"

I'll also mention a little circular piece I once overheard a drunken friend reciting to himself:

"I like cider, but cider makes me fart, and when I fart I smell, and when I smell people give me money to go away.  With that money I buy cider..."

Finally, I'd like to redirect you this this thread here:

http://www.thenakedscientists.com/forum/index.php?topic=29003.msg301779#msg301779

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Geology, Palaeontology & Archaeology / What do we know about the large Feb 2010 Earthquake in Chile?

« on: 27/02/2010 13:15:59 »

The USGS Google Earth Quakes plugin shows the quake as 8.8 and was centered just about 5km offshore, and about 35km deep.

Looks like there have already been a slew of 5's & 6's (up to 6.9) N & S of it.

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Just Chat! / Does anyone know what this is or what's going on here?

« on: 20/01/2010 20:57:26 »

The Google Maps link below points to an area near Xtobob, to the West of Mérida, Yucatán, Mexico, but I can't find any references to what's going on there.  Interestingly, if you zoom out a couple of times it disappears and there just seems to be trees there, indicating that it's relatively new.

http://maps.google.co.uk/?ie=UTF8&ll=20.965126,-89.788942&spn=0.074298,0.075445&t=h&z=14

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Geology, Palaeontology & Archaeology / How frequent are Earthquakes off the British Columbian coast fault?

« on: 16/12/2009 15:29:56 »

I just noticed (using Google Earth) a recent 4.5 quake off Kunghit Island, British Columbia, and while it's not a terribly strong quake it looks rather isolated.  Any comments?

9

Plant Sciences, Zoology & Evolution / Why do hoverflies hover?

« on: 23/11/2009 15:25:26 »

What are hoverflies doing when they're just hovering in the air, apparently doing nothing useful?

Other flying insects are able to navigate and track scents while moving, and as far as I can see, just hovering in the same place would only seem to make it an easier target for predators.  However, as they've obviously still around and weren't all eaten long ago, hovering must serve some constructive purpose that outweighs the risk of being eaten.

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Physics, Astronomy & Cosmology / Where is our local quasar remnant?

« on: 30/10/2009 17:13:48 »

If we accept that the universe is fundamentally the same everywhere, then an observer in the regions where we now see quasars should, when looking towards us, see quasars somewhere in our region of space.  Because such an observer will be seeing our past, just as we see theirs, we shouldn't expect to see an active quasar in our region of space, but we should see the remnants of one, or perhaps a few, quasars fairly close to us.

Does anyone know of any candidates for such quasar remnants nearby?

Incidentally, the current model for quasars involves material falling into very large Black Holes (wikipedia says):

"there is now a scientific consensus that a quasar is a compact region 10-10,000 times the Schwarzschild radius of the central supermassive black hole of a galaxy, powered by its accretion disc."

and also:

"Large central masses (10⁶ to 10⁹ Solar masses) have been measured in quasars using 'reverberation mapping'."

Now even if a quasar has quietened down over the billions of years since it was active, the region of space around it should still be brighter than the CMBR, and remember too that this isn't a tiny thing we're looking for here, but something that's pretty big, mass-wise.  Also, don't forget that the larger a Black Hole is, the colder it is and therefore the more slowly it will evaporate due to Hawking radiation, so these super-massive galactic mass Black Holes should still be around.

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That CAN'T be true! / Is this the silliest way to calculate Pi?

« on: 05/07/2009 13:06:41 »

I once mentioned in an old and long forgotten thread that Pi could be calculated using random numbers, and I've finally got around to coding something to try it out[]

Basically, you generate pairs of random x & y coordinates then use Pythagorus to see if the coordinate falls inside or outside a circle (I actually got it wrong in the earlier thread - it's the number of points that fall inside the circle divided by the total number of iterations, and not the number that fall outside the circle, as I'd said earlier.  To simply things I just used a quarter circle so I could just use values 0 < n < 1 and then multiplied the result by 4)

Anyway, after four runs of 10,000,000 iterations I got these results:

3.14275271428
3.14078311408
3.14159111416
3.14055391406

which gives a mean average of 3.141420214145.

Pretty poor results for the number of iterations, I think  []

12

Physics, Astronomy & Cosmology / How important is phase in electron-positron pair creation?

« on: 22/06/2009 18:48:51 »

When an electron/positron pair is created from a pair of gamma photons, how important is the relative phase difference between the two gamma photons?  Does it have any significance at all?  I'm wondering this because it would seem to me that the probability of any two gamma photons meeting exactly in-phase is likely to be tiny, but I get the impression that electron-positron pair creation is relatively common.

13

Plant Sciences, Zoology & Evolution / Were dinosaurs skinnier than we thought?

« on: 22/06/2009 17:31:49 »

It looks as though they may have been.  If this is so, it's going to mean that a lot of stuff that's been extrapolated from what we thought we knew, ranging from food requirements to speeds, will need to be re-done.

http://www.theregister.co.uk/2009/06/22/dinosaur_weight_revisionism/

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Just Chat! / Latest Haynes Owner's Workshop Manual

« on: 11/06/2009 13:10:28 »

I don't know how widely known they are outside the U.K., but Haynes are about to release the latest in their series of commemorative OWMs:

http://www.theregister.co.uk/2009/06/10/apollo_owners_manual/ []

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Physics, Astronomy & Cosmology / What is the significance of the Planck units in QM?

« on: 18/05/2009 18:48:44 »

While I've seen some of the Planck units, such as the Planck Distance and Planck Time, being described as the smallest values that make any sense in QM, some of the other (derived) Planck units are quite large, and the Planck Temperature represents a maximum rather than a minimum value, so it must be possible to work with sub-Planck unit values.  This seems contradictory to me.

There also seems to be another practical problem, regarding the Planck Distance and Time units, in that working with sub-light speed values requires using values of < 1 Planck Distance/Time.  For a large object, composed of many particles, I could see how its average speed could be < c by statistical averaging of each of the individual particles velocities but when you consider the movement of a single particle you hit problems, especially if the particle is accelerating/decelerating.

If you consider a very slowly moving particle, it seems to me that it must either be constantly moving over either < 1 Planck Distance for each Planck unit of time, or it must take a varying number of Planck units of time to move one Planck Distance unit.  At high speeds though, even taking a varying number of Planck Time units to move a single Planck Distance unit is problematic; when traveling at 0.5 c you'd take two Planck Time units to travel one Planck Distance, which is fair enough, but then what happens when you travel at 0.75 c?  You then need to deal with fractions of Planck Time units.

16

Just Chat! / Stream of conciousness generator

« on: 11/03/2009 00:02:03 »

I've been playing around with some simple word-pair scoring and traversal routines and have come up with something that's generating stuff like...

Query word was: birth
----------------
It is produced by the impactor and the most of cheese and on the point of it is made from the inlet that they were enabled us and it continues moving away from which we found in which seemed to the north and in the range of the birth of a very high round snowy mountains that the same chain being turned to be a mile from a few scattered trees and a league in a small moons .

Prompt word was: birth
-----------------
At one of material may be used for the cheese is formed by a number of Sir Henry at the bombing during birth .

Prompt word was: birth
-----------------
In the entrance into the fog entirely covered with the birth of his father had been the milk in his life .

Prompt word was: blown
-----------------
It is produced by the impactor and the most of cheese and on the sky, enabled us and it is made from the point of ancient crystalline rocks blasted away from which seemed to the inlet that we found in the range of the north and in which we had constantly blown out, picking their own .

Prompt word was: the
-----------------
It is produced by the impactor and the most of cheese and on the point of it is made from the sky, enabled us and it became clear away from which we found in which seemed to the north and in the range of the same chain being turned to be a very abrupt manner, with a mile from a few scattered trees and a league in a small moons .

Prompt word was: saw
-----------------
Most cheeses such as the fog entirely covered with the appearance of snowy mountains that the inlet that we dined, and from milk, and Sir Henry, but it was one of Sir Henry at the name of a number of material may be used for the ship saw the milk in an impact craters .

Prompt word was: show
-----------------
In the entrance into the Peel show involved bizarre characters that they were not to form a low sandy point now, he was a good sleep .

The output clearly reflects the limited data I've input to it, so far, and there's currently only just over 13000 word pairs in the db, but I think it's encouraging []

For some reason, the old saying "The Devil finds work for idle hands" comes to mind  []

17

Guest Book / Forum suggestion

« on: 10/03/2009 18:14:22 »

I'd like to suggest that the ability to edit forum Topic Headings and the original question is removed.

A few times now, I've noticed that some people who have started new topics have later amended the Topic Heading, and sometimes even the original question, for their topic in response to some of the comments posted in the subsequent thread.  The trouble with this is that the responses that have already been posted sometimes no longer seem to be relevant or make any sense in the context of the amended question.

While being able to edit a response to a question is sometimes necessary, to correct mistakes and typos, I think it might be a good idea to disallow this for the original question.  If someone honestly decides that they've made a mistake in their original question then perhaps it would be better for them to delete the topic, if no one has yet responded to it, and then start another new topic with the question correctly framed.

I find it difficult to imagine any good reasons for editing either the Topic Heading or the original question after people have started posting replies to it; all it will do is confuse people who try to read the thread at a later date.

18

Just Chat! / Our Karma ratings

« on: 08/02/2009 23:44:16 »

I couldn't help noticing that my karma rating initially went up but then went back down again, indicating that rather than support someone of whom they approved, some people would rather put down people of whom they disapprove.  I think I now understand why it's labeled Karma  []

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That CAN'T be true! / Can we trust all studies produced by reputable universities?

« on: 11/12/2008 14:09:14 »

Link to an article reviewing a report produced by the University of Sheffield that has been used as justification by the government to raise duties and increase regulation of booze.

http://www.theregister.co.uk/2008/12/11/alcohol_pricing_sheffield_study/

20

Physiology & Medicine / Is worry about nuts making us nuts?

« on: 10/12/2008 18:55:24 »

Below is a link to a 'popular' news article, about an item concerning hysteria published in the BMJ.

http://www.theregister.co.uk/2008/12/10/nut_allergy_hysteria/