Posts by LivingDog

1) Message boards : Cafe Einstein : An Anomalous SETI Signal (from APOD:NASA) (Message 110236)
Posted 1451 days ago by Profile LivingDog

2) Message boards : Cafe Einstein : Out of DATA?? (Message 108868)
Posted 1497 days ago by Profile LivingDog
Thanks tolafoph and MAGIC. I set it to 0% and she is running again as usual. PS: Don't remind me of how much time I lost on this machine! It already hurts enough. :( Can I get wu's on my cell phone?? (j/k)

Thanks again guys.
3) Message boards : Cafe Einstein : Out of DATA?? (Message 108827)
Posted 1498 days ago by Profile LivingDog
I must not have understood. I checked the client on my G4 and it's still getting wu's. But now, the "TASKS" tab shows no wu's on my PC. My E@H has been getting this strange message for a few days:

12/21/2010 8:49:51 AM Suspending computation - CPU usage is too high
12/21/2010 8:50:01 AM Resuming computation
12/21/2010 8:50:21 AM Suspending computation - CPU usage is too high
12/21/2010 8:50:31 AM Resuming computation
12/21/2010 8:51:31 AM Suspending computation - CPU usage is too high
12/21/2010 8:51:41 AM Resuming computation

It's never gotten those before. Besides that, with no wu's WHAT is being "resumed"?? So what did I do wrong? I confess, I played with the preferences (mae culpa) but then reset to the web defaults - the ones I always use. Now everything is sad in wu-ville.

Should I uninstall/reinstall in order to fix this problem?

thx in advance,

4) Message boards : Cafe Einstein : User .... Of ....The...... Day (Message 108776)
Posted 1499 days ago by Profile LivingDog
4+ million as a single user!!! I have wu-envy! :)

5) Message boards : Cafe Einstein : Out of DATA?? (Message 108711)
Posted 1500 days ago by Profile LivingDog
I was wondering why my messages said "out of data." I read the technical news and I think it means they stopped using the BOINC client and are getting ready to switch to a newer better stronger faster one. Am I correct? Let's go, I need my fix... my machine is sitting in idle... SHUT IT DOWN!?!? *sigh* ... I NEED MY WUs!!!

6) Message boards : Science : Not Gravity, Geometry? (Message 104779)
Posted 1686 days ago by Profile LivingDog
hi Mike,

I have looked only briefly at all of your last replies. Right now I am reading Box 1.6 "Curvature of what?" of MTW. Then I will read and reply to your latest set of posts in this thread. BTW, thanks for all the help. Conceptual discussions of physics are a very good and rare thing - so they should always be appreciated. But w/o formalism, they can lead ... any where - good or bad - true or false - and so be leading or misleading. Physics is both equations and concepts. It requires both to have a good (concepts) and solid (formalism) understanding of physics.

When I was an undergraduate student I was told that MTW is called the "Princeton Phonebook" b/c of all the Princeton professors it references. I referred to it as "MTW's blerb about GR" as a joke. Joke may be on me b/c MTW is half as long as the Bible ... and it took me ~3 years to read that.

Anyway, page 32 of MTW says that Riemann "... spent his dying days at 40 working to find a unified account of electricity and gravitation." This didn't gel with your description so I went to for his bio to clarify. This is from their page on Georg Friedrich Bernhard Riemann

Austro-Prussian War

Riemann fled Göttingen when the armies of Hanover and Prussia clashed there in 1866.[1] He died of tuberculosis during his third journey to Italy in Selasca (now a hamlet of Verbania on Lake Maggiore) where he was buried in the cemetery in Biganzolo (Verbania). Meanwhile, in Göttingen his housekeeper tidied up some of the mess in his office, including much unpublished work. Riemann refused to publish incomplete work and some deep insights may have been lost forever.

British TV: I've been a fan.
Wallace & Gromit, Jeeves and Wooster, Carry on Regardless, MPFC, The Rise and Fall of Reginald Perrin, Fawlty Towers, Blackadder, The Young Ones, RED DWARF (the first 6 seasons only), almost any Peter Sellers movie, Shaun of the Dead, Are You Being Served, Yes Minister, Yes Prime Minister, Rumpole of the Bailey, ... the list goes on.

7) Message boards : Science : Not Gravity, Geometry? (Message 104756)
Posted 1688 days ago by Profile LivingDog
I originally asked, "In GR, how does the gravitational force, F = GM1M2/r^2, become geometry?" To which Mike replied (the quotes) and then my replies below his replies. (I edited the 'hec' out of the quotes and lost the original flow. So now I have to explain the above... like a pendulum do.)

These are words which are really 'external' descriptors. Riemann's way of deducing this equivalently was to say : I have a point on the apple and I compare two paths diverging from that point, further down each path I find they meet each other again. He comes up with a 'value' at each point on the apple, such that if one considers the totality of all these values you could arrive at what it would look like if you did see the apple from afar.

May I have some of the math? I have an MS in Physics, and have taken a GR course (millennium ago), and am now reading the Princeton Phone book (MTW's blerb about GR).

E.g. are you refering to the affine connection? [tex]\Gamma^{\alpha}_{\mu\nu}[/tex] the metric tensor?? [tex]g_{\mu\nu}[/tex] BOTH???

"Why no tex? ... you have no tex!?! AHHH!! HE HAS NO TEX!!!" (apologies to Mike Judge)


- to split the problem into two parts. Begin by stating the geometry in terms of what distribution of matter/energy produces it,


then given that, see what response some object has in that geometry. Hence 'matter tells space how to warp, and space tells matter how to move'.

OHhhh... I see. Since the mass moves in a way according to the spacetime!

- spacetime is flat whenever viewed from close enough. This means that for a short enough time and/or for a small enough distance any movement looks Euclidean ( or Gallilean or Newtonian ).

Yes, b/c measurements have a certain precision. "Flat" really means "I cannot measure curvature below the precision of my equipment."

So thirdly : how do you describe movement in detail in this framework? Well those 'values' I mentioned above are really a set of values at each point in spacetime. They 'explain' how you transition from one point to the next if you are freely falling ( only subject to gravity ). This is where the 'warping' business comes in : at each point in spacetime where gravity is acting ( and gravity is everywhere acting on everything ), these 'metric tensors' are a local guide to how directions change and thus which way to go next.

Yeah... so the mass distribution (typically a sphere, ala Scwarzschild) determines [tex]g_{\mu\nu}[/tex] and then that determines the proper interval. [tex]g_{\mu\nu}[/tex] tells things how two points are connected - "curved" via [tex]g_{\mu\nu}[/tex] or "flat" via [tex]\eta_{\mu\nu}[/tex].

Right, in short: [tex]ds^2 = g_{\mu\nu}dx^{\mu}dx^{\nu}[/tex]

Fourthly : I have left light out thus far. In GR the phrase 'straight line' is replaced by 'the path that light follows' or 'null geodesic'.

Is this the role of the Killing vector? If one solves for X in the Killing equation, then one knows the Killing vector, which is the path of a photon in this metric (with given mass distribution), which is called the "geodesic". IOW, solve for X in:

[tex]X_{\mu};_{\nu} + X_{\nu};_{\mu} = 0[/tex]

For ordinary life these are easily seen to be the same thing. If you can arrange matters to view three objects by eye and see that they overlap/occult one another simultaneously then we say they are in a line.

Right... we say they are in a "straight" line, but in reality they are following along the geodesic! Yes?? :)

The time component comes out as a change in the frequency of the light radiation, and thus is a measure of how time (i.e. clocks) varies around and about.

Ohhh, so that's how we know the spacetime is curved - by the change in the color of the light as it travels from one point to another. Yes?? :(

Yes, on the light cone analogy. I think I am understanding it now.

we have an approximate but not exact solution to the GR equations for this.

I thought it was exact. Was this the problem with the cosmological term?

It was figured out by an artillery officer on the eastern European front in WWI, and he died not long after mailing it to Einstein. It's the ( Karl ) Schwartzchild (maybe without the 't' ?) solution,

Oh wow... I did not know that. What a shame.

Personally I try to avoid the word 'curvature' or at least mentally substitute it with the phrase 'observers differ'. That way time can be 'curved' by differently situated clocks progressively disagreeing with each other.

Well, if my replies are correct, then I can accept curvature since it is really how two points are connected - "geodesic-ally" - via the [tex]g_{\mu\nu}[/tex]. Yes?

Thanks Mike!
8) Message boards : Science : Have the interferometers been "zero" tested? (Message 104735)
Posted 1689 days ago by Profile LivingDog
... if four or more respond to a wave ...

Four or more? How many are there? I thought there were only 2 - LIGO and GIGO.

Any future plans to put one on the moon? Seems like an ideal place since there are no vibrations other than the low tidal forces from the Sun/Earth system.
9) Message boards : Science : Have the interferometers been "zero" tested? (Message 104729)
Posted 1690 days ago by Profile LivingDog
Some time ago I learned that anytime one does an experiment one should always do what I call a "zero" test. (Maybe there's a more professional/standard nomenclature?) It's a kind of calibration - to make sure your equipment is working as it should.

Basically all you do is measure a known quantity. E.g. if you build a new voltmeter you could connect the leads to measure the potential difference. If you see anything other than 0 you know something is amiss with the equipment/design/whatever.

The reason I ask is that it seems impossible. How can you test for gravity waves when no one has ever _measured_ gravity waves???

So has any one done a "zero" test of the interferometers?

Thanks in advance for any replies...
10) Message boards : Science : Not Gravity, Geometry? (Message 104418)
Posted 1699 days ago by Profile LivingDog
In GR, how does the gravitational force, F = GM1M2/r^2, become geometry?

Ah, now that is a core question. It may take more than a bit of explaining though .... and beware there is no neat/pat answer that will likely satisfy your intuition. It really is quite a paradigm shift. Go and get a cup of your favorite brew before reading. I'll give you Mike's Tour Of GR! :-)

Firstly : ...

Secondly : ...

So thirdly : ...

Fourthly : ...

So finally ...

Thanks for the PG Tips.


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This material is based upon work supported by the National Science Foundation (NSF) under Grants PHY-1104902, PHY-1104617 and PHY-1105572 and by the Max Planck Gesellschaft (MPG). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the investigators and do not necessarily reflect the views of the NSF or the MPG.

Copyright © 2015 Bruce Allen