Using the force constant in equations

marcus · Mar 20, 2005

thomson scattering cross-section of electron

earlier I was making lists of like a dozen or so basic constants
that are used so much they are worth remembering

the REALLY basic constants are all one, in this system, so they are not hard to remember

but then there is the next layer, like the mass of the electron is 2.1E-22 mass units

even that is not so bad because the rest-energy of the electron is the same number...2.1E-22 energy units.
and the Compton wavelength is just the reciprocal of that
1/(2.1E-22) length units.

well there is something called the "Classical Radius of the Electron"
which is just 1/137 times the Compton.

so it is something I can calculate just from knowing 1/137 and 2.1E-22

and the THOMSON crosssection which tells the probability that an electron left to its own devices will scatter some light is simply

[tex]\sigma_{\text{Thomson}} = \frac{8\pi}{3}(\text{classical radius})^2[/tex]

I am having trouble getting the LaTex to work so for redundancy I will just type out what I was trying to write

sigma-sub-Thomson = 8pi/3 x (classical radius)²

once you have the thomson crosssection then (as that U. Texas link shows) you have to tack on a term that shows how the resonant frequency of the molecule affects the scattering probability, but the basic thing that there is any scattering at all comes from the Thomson, which is just 8pi/3 times the square of the classical radius.

It isn't important but I might as well calculate the thomson scattering crosssection

the radius is
1/(137 x 2.1E-22) = 3.48E19 natural length units

squaring and multiplying by 8pi/3 gives
1.01E40 natural area units.

wow. that is weird. the interaction of an electron with light is a little area which in these units comes out to right around E40 area units.

just as a check I converted that to metric and it was about 6.6E-29 sqmeters. wow again. that is what the U.Texas website on this gives!
getting the answer their conventional way involves looking up constants and multiplying a lot of stuff together because the formulas are more complicated but comes to the same thing.

marcus · Mar 20, 2005

I like the E40 area
when i walk out into the garden on a bright morning
I see the temperature of the sun is 2E28 natural
(and that is very close: has a couple of decimalplaces unstated precision)

and in the sky each molecule is holding out a card with this area E40
which shows the probability that a photon passing thru will bump it

and the rayleigh scattering section showing dependence on the photon frequency is just that E40 area units multiplied by

the fourth power of the freq. ratio-------(omega_photon/omega_resonant)⁴

so the blue overhead is talking about a small area with a simple formula namely

[tex](\frac{\omega_\text{photon}}{\omega_{\text{resonant}}})^4 E40 \text{ natural units}[/tex]

marcus · Mar 21, 2005

marcus said:

when i walk out into the garden on a bright morning
I see the temperature of the sun is 2E28 natural
...

I guess it has become a custom with me (might be too much to say an observance or a kind of mantra)

to go outside in the morning, or if it's raining wait tlll the sun comes out, and
be aware of some numbers that go along with the experience

first thing is the sun (you can tell by the color it glows) is really hot 2E-28
and our speed going around it is E-4
and a year is E50

and the thomson area E40 that makes the sky scatter light
(which when you correct with the fourthpower rayleigh factor explains the blue)

and the colors red-end 7E-28, green 10E-28, blue-end 13E-28
these being frequencies (photon energies, same number) that you would expect to get from something the sun's temperature

and the leaves look green because they are eating the red and blue but not the green in between.

the temperature of the air around me is like E-29, and inside me it's 1.1E-29

and that thomson area E40 comes straight from the mass of the electron 2.1E-22 and the number 1/137

and there is sound, like birds and maybe some distant freeway noise,
maybe I played the treble D on the piano just before I stepped outside E-40

and the speed of sound, which relates the pitch of a bird's call to the size of its throat and governs all kinds of resonance like that...

and then there is breakfast to think about... taking on a little energy...

marcus · Mar 21, 2005

brunch might be a hundredth of a natural energy unit
since the sun is out there and I feel its warmth I might remember
that it has to make E20 helium atoms in order to release one natural unit of energy.

i am vaguely aware that i am standing on a sphere. its girth at the equator is about 50E40

standing in the garden I feel a force of E-40 on the sole of each foot.

(telling me something about the Earth's mass and mine)

it was really windy yesterday, today it's calm, which says something about the temperature gradient and the threshold for convection

I should say that the mass of a proton is 1836 x 2.1E-22
and the mass of an air molecule is 29 x 1836 x 2.1E-22.
that will tell me the threshold for wind: it is 2/7 times the weight of a molecule of air.

time to take a walk up the hill in back of campus.
idleness punctuated by numerical musing

marcus · Mar 22, 2005

In natural units the Unruh temperature that goes along with an acceleration a is very simple

[tex]T_\text{unruh} = \frac{a}{2\pi}[/tex]

You just have to get the acceleration that something experiences, expressed in natural units, and divide by 2pi. That gives the temperature of the thermal radiation seen in the accelerated frame.

Unruh temperature = acceleration/2pi

in the RHIC, heavy ion collider, stuff is decelerated from the speed of light down to zero in a distance they put at 0.2E-15 meter, which is 2.5E18 natural length units.
that means it is taking about 5E18 time units to come to a stop, from the speed of light.

Order of magnitude, the acceleration is 2E-19 natural units, so divide by 2pi and you get a Unruh temperature of 3E-20

this around a 100 million electron volts. basically what the RHIC people say.
http://www.bnl.gov/rhic/black_holes_kharzeev.htm

compare this Unruh temp to the surface of the sun which is 2E-28.
it is about 100 million times hotter than the solar surface.
so there is some thermal radiation which the experimenters have evidence of. I don't know if they are interpreting their findings right or not. I calculate the same Unruh temperature they do but I can't vouch that this is what is going on.

Meanhippy provided the original link for this:
http://www.bnl.gov/rhic/black_holes.htm

"Horatiu Nastase, a member of the high-energy physics theory group at Brown University, has written a paper, posted on the preprint website arxiv.org, in which he claims that collisions at Brookhaven’s Relativistic Heavy Ion Collider (RHIC) produce the analog of a black hole..."

They are not talking about Hawking radiation from a black hole, they are talking about Unruh radiation from acceleration which is ANALOGOUS to Hawking radiation from a black hole.
Bill Unruh at UBC Vancouver discovered his temperature and his radiation right around the same time as Hawking discovered the other kind.
The two formulas are very similar.

Here is the technical article by Nastase that goes with the news item.
http://arxiv.org/abs/hep-th/0501068

marcus · Mar 23, 2005

in conventional nuclear engineering and physics there is the familiar blue light in the tank of water----the cerenkov effect light.

you can tell the energy of a beam of electrons going thru water by the cerenkov angle, the angle that the light diverges from the direction of the beam.

the cerenkov rays make a cone of directions at a fixed angle from the direction of the beam

if you tell a physicist the angle, he or she will tell the energy of the electrons in MeV, or eevee.

we have to use electronQUARTERvolts, or "eQ" pronounced "eekyoo"

because E-28 of the natural voltage unit is a quarter of a conventional
and E-28 of the natural energy unit is a quarter of a conventional eevee
too bad the historically accidental metric volt is 4 times too big tough luck that is just how the cookie crumbled

so here is a problem, to keep in practice with natural units:
suppose there is a beam of electrons in water and the cerenkov angle turns out to be 30 degrees
what is the kinetic energy of one of the electrons?

[tex]\cos \theta = \frac{\text{speed of light in water}}{\text{speed of electron}}[/tex]

I guess the best would be to first find the speed.

the speed of light in water is 0.75 natural units

marcus · Mar 23, 2005

This summary description of the units needs to be brought forward periodically, to keep it accessible. the latest copy is post #245, which is a ways back. So I will reproduce it here:

the force F = c⁴/(8piG) is the main constant in Gen Rel, the prevailing theory of gravity since 1915. The constant in the Einstein equation is not Newton's G, but rather F. In Quantum Gravity one often uses units in which |F| = 1
(this can come about by stipulating that |8piG|=1, since normally one already has adjusted the units so |c|=1)

the moment one sets
|F|= |c|=|hbar|=|k|=|e|=1
one has a fairly universal set of units and it is interesting to see what some familiar quantities come out to be.

Another way (suggested by a Kea post) to define the same units is to make the unit angular frequency be 3.7E42 per second. Call it Z, just to have a symbol. Adjusting the units to make the value |Z| = 1 gives the same set of units as setting |F| = 1.

I am trying out this version of natural units to see how they work. In order to try out the units one must keep a list of rough sizes of things handy----to use the units for practical purposes one must have a sense of scale. Here are some rough sizes of familiar things expressed in the units.
I periodically bring this list forward to keep it handy.

rough sizes:

Code:

q'ty expressed in nat.     approximate size
E8 mass             pound
E50 time units       year
E33 length           handbreadth (3.2 inch, 8.1 cm)
E34 length           pace
E37 length           half mile
E50 length           lightyear
E-5 energy           food Calorie 
E-8 energy            lab calorie 
E-28 voltage          quarter volt 
E-28 energy          quarter eV
10E-28 energy        typical photon energy for green light
E-53 electmagn.field unit     tesla 
E-57 field unit             gauss
E-29 temperatrure     average Earth surface temp
E-9 speed           2/3 mph
E-7 speed             67 mph
E-6 speed             speed of sound (cold air)
E-107 pressure      conventional PSI on airgauge
14E-107               normal atmospheric pressure
E-39 (ang. format) frequency   D on treble staff
E-50 acceleration   one "gee"
E-40 force          weight of 50 kg sack of cement, traditional "hundredweight"
E-49 power        144 watt bulb

some constants (approx.):

reciprocal proton mass 2.6E18
electron mass 2.1E-22
Hubble time 1.6E60
Lambda 0.85 E-120
rho-Lambda 0.85 E-120
rho-crit (critical density) 1.16 E-120
more exact Earth year 1.1676 E50
more exact lightyear 1.1676 E50
avg Earth orbit speed E-4
earth mass 1.38 E33
earth radius 7.86 E40
sun mass 4.6 E38
solar surface temp 2.0E-28
sun core temp 5E-25
solar constant 6.2E-117
CMB temperature 9.6E-32
earth surface air pressure 1.4E-106
earth surface gravity 0.88E-50
fuel energy released by one O₂ 17E-28
density of water 1.225 E8/E99

timescale:
3.700E42 rad per sec 1 (the unit frequency)
1/222 of a minute E42
4.5 minutes E45
As a handle on the natural timescale, imagine counting out loud rapidly at the rate of 222 counts a minute, each count is E42 natural time units. A thousand counts is 4 and 1/2 minutes. It just happens that one year is roughly E8 counts, or E50 natural.

marcus · Mar 23, 2005

marcus · Mar 23, 2005

about the cerenkov problem earlier

...suppose there is a beam of electrons in water and the cerenkov angle turns out to be 30 degrees
what is the kinetic energy of one of the electrons?

[tex]\cos \theta = \frac{\text{speed of light in water}}{\text{speed of electron}}[/tex]

I guess the best would be to first find the speed.

the speed of light in water is 0.75 natural units

I think it is clear that the electrons are traveling at 0.866 speed unit.
so an electron's total energy is twice its energy at rest
which is 2.1E-22

so the kinetic energy is 2.1E-22 we don't have to convert that to "eekyoo"
but since an eQ is E-28 this amount would translate to 2.1 million eQ.
(around half a conventional MeV, if you like it so)

if anyone is following the thread and wants more detail on this please say, would be happy to provide it

marcus · Mar 26, 2005

One reason I had for practicing with these variant Planck units, in a thread like this, is because of a feeling that they are replacing conventional Planck units in QG research.

this is illustrated by what you can see martin bojowald doing in his most recent Loop Quantum Cosmology paper.
http://arxiv.org/gr-qc/0503020

On page 3 right after equation (8) he simply defines the Planck length by

[tex]l_P = \sqrt{8 \pi G \hbar}[/tex]

so he is not walking on tiptoe he just flat-out explictly says "the Planck length is such and such" and it turns out to be the very same thing I have been calling "natural length unit" in this thread

it comes out to 8.1E-33 centimeter.
(c is already understood to have value unity)

I believe I must have seen that before but just wasnt sensitized to it.

well so the width of my palm is E33 Planck length, and I don't have to say E33 "natural length units" all the time, to keep reminding that these are variants of the older Planck units.

marcus · Mar 27, 2005

In another thread Fibonacci was asking what is the matter density in space
https://www.physicsforums.com/showthread.php?p=505249#post505249
and there were several answers offered depending on if he meant the overall average density of (visible? baryonic?) matter in the universe, or should it just be the amount of stuff in the space between stars in our part of the galaxy, or what?

I have to try answering this is natural units terms. the critical density, needed for the observed flatness, is the usual benchmark and it is
order of magnitude E-120

but if we need accuracy then 1.16E-120

and visible or baryonic matter is ordinarily estimated to be 4 percent of critical, so around 5E-122.

we need to imagine some volume, let's take an 81 cm step, roughly 2 and a half feet-----E34 natural length units----and consider the "cubic pace" volume which is E102 natural.
then the ordinary matter in the universe averages out to 5E-20 mass units inside that cubic pace volume.

a proton mass is about 4E-19. so in that cubic pace the average is roughly a tenth of a proton, order of magnitude.

In the space between stars in our galaxy it might be tenfold larger or one proton mass per cubic pace, just as a rough guess. but this estimate is overall including galaxies and the empty space between them, all averaged out

marcus · Mar 27, 2005

one thing I'm trying to do is sort out a small set of essential numbers which if you have them on a piece of paper by the computer can tell you the rest

for example I remember that in natural units the Hubble radius is 1.6E60
and in anybody's system of units the visible or baryonic matter is 4% of critical

that is enough to answer a wide range of questions:
the Hubble time is 1.6E60
the Hubble parameter H₀ is the reciprocal of that, namely (1.6E60)^-1
critical density is 3 times the square of the Hubble parameter
so if I ever forget it I can just go 3/1.6² and see that
critical is around 1.16E-120
I can take 4 percent of that and get the density of ordinary matter.
Or take other well known percentages to find the densities of other stuff like dark matter and the hypothetical dark energy.

So it comes down to remembering that the Hubble time is 1.6E60 natural time units (or, since it is the same number, that the Hubble length is 1.6E60 length units)

marcus · Mar 27, 2005

marcus said:

One reason I had for practicing with these variant Planck units, in a thread like this, is because of a feeling that they are replacing conventional Planck units in QG research.

this is illustrated by what you can see martin bojowald doing in his most recent Loop Quantum Cosmology paper.
http://arxiv.org/gr-qc/0503020

On page 3 right after equation (8) he simply defines the Planck length by

[tex]l_P = \sqrt{8 \pi G \hbar}[/tex]

so he is not walking on tiptoe he just flat-out explictly says "the Planck length is such and such" and it turns out to be the very same thing I have been calling "natural length unit" in this thread

it comes out to 8.1E-33 centimeter.
(c is already understood to have value unity)

I believe I must have seen that before but just wasnt sensitized to it.

well so the width of my palm is E33 Planck length, and I don't have to say E33 "natural length units" all the time, to keep reminding that these are variants of the older Planck units.

The same pattern again, this time with a worldclass cosmologist in a survey article summarizing the state of his field. He just comes right out and says that the Planck mass is equal to the new value: 2.4E18 GeV.
check out page 9 of this definitive overview of current status of cosmology

http://arxiv.org/abs/gr-qc/0503107
Understanding Our Universe: Current Status and Open Issues
T. Padmanabhan
To appear in "100 Years of Relativity - Space-time Structure: Einstein and Beyond", A.Ashtekar (Editor), World Scientific (Singapore, 2005); 30 pages; 4 figures

"Last couple of decades have been the golden age for cosmology. High quality data confirmed the broad paradigm of standard cosmology but have thrusted upon us a preposterous composition for the universe which defies any simple explanation, thereby posing probably the greatest challenge theoretical physics has ever faced. Several aspects of these developments are critically reviewed, concentrating on conceptual issues and open questions. [Topics discussed include: Cosmological Paradigm, Growth of structures in the universe, Inflation and generation of initial perturbations, Temperature anisotropies of the CMBR, Dark energy, Cosmological Constant, Deeper issues in cosmology.]"

Padmanabhan does not mess around, on page 9, when it comes time to, he just says

[tex]M_P = (8\pi G)^-^1 \approx 2.4E18 GeV[/tex]

apparently Ashtekar's nickname for Thanu Padmanabhan is "paddy"

lets double check that Padmanabhan figure for Planck mass is correct.
for us the eekyoo or electron quartervolt is E-28 of Planck energy, so Planck energy is E28 eQ
which is roughly 0.25E28 eV = 2.5E27 eV = 2.5E18 x E9 eV = 2.5E18 GeV.
OK Padmanabhan is right. actually an eekyoo is 0.24 eV, it is only approximately a quarter, it is really 0.24 instead of 0.25.

marcus · Mar 27, 2005

Just an aside about Ashtekar's book "A Hundred Years of Relativity" to be published by World Scientific this year.

It will have a chapter by Martin Bojowald too!

looks like it might be a very good book, with a definitive chapter on cosmology by Padmanabhan and a definitive chapter by Bojowald on current state of quantum cosmology (LQC)

Towards the end of paddy chapter he has some questions to ask of quantum gravity, basic things that cosmology needs to know, he does not give QG such a good report card. On page 25, he says:

"The second question is: How (and why!) was the universe created and what happened before the big bang? The cosmologist giving the public lecture usually mumbles something about requiring a quantum gravity model to circumvent the classical singularity - but we really have no idea!. String theory offers no insight; the implications of loop quantum gravity for quantum cosmology have attracted a fair amount of attention recently [45] but it is fair to say we still do not know how (and why) the universe came into being."

[EDIT] sorry about the unfortunate confusion over the words "was created"! I should have realize that could suggest a conscious creator and eliminated the words. What Padmanabhan more likely meant is how he pHrased it the second time "came into being". That is more impersonal and more in keeping with scientific inquiry in general and cosmology in particular. When i posted the quote it did not occur to me that anyone would read it as suggesting anything other than simply "came into being".[/EDIT]

nightcleaner · Mar 28, 2005

Hi Marcus

Assumption: the universe was created. (whoooo boy, hot topic. I pray we not get into a creationist debate.)

Assumption: there was time and space before the "big bang" (well there has to be if there is going to be a creator going around creating stuff?)

an idea: the "creation" is ongoing and can be observed right now by investigating conditions at very small scales. This is a generalizing reformulation of the concept from Biology that ontology recapitulates ontogeny. If I remember it right, ontology is the study of how organisms form from reproductive cells. A single cell becomes an entire organism. Ontogeny is the study of how species evolve from simpler species (cheese! crossing the creationists again.)

Well we can watch a single cell become an organism. The idea is that the single cell retraces the steps that the species went through in evolving. First it is like an amoeba, then it is like a worm, then it is like a fish, then like a reptile, then like a mammal, and so on. It isn't a very exact process. Lots of the steps can be left out without losing anything, so eventually the genetic instructions for those steps are deleted.

I am surprised to see a world class cosmologist asking this how and why question.

Thanks for the conversation.

nc

selfAdjoint · Mar 28, 2005

nightcleaner said:

Hi Marcus

Assumption: the universe was created. (whoooo boy, hot topic. I pray we not get into a creationist debate.)

Well, honestly, nightcleaner, if you assume a creator you're going to get static from those who, like Laplace, have no need for that assumption.

Assumption: there was time and space before the "big bang" (well there has to be if there is going to be a creator going around creating stuff?)

Not necessarily. The Bible says "without form and void", and some of the causal triangulations proposals could fulfill this. To mathematicians and some physicists, fully metric spacetime is a very special idea that could be preceded by several more general states.

an idea: the "creation" is ongoing and can be observed right now by investigating conditions at very small scales. This is a generalizing reformulation of the concept from Biology that ontology recapitulates ontogeny. If I remember it right, ontology is the study of how organisms form from reproductive cells. A single cell becomes an entire organism. Ontogeny is the study of how species evolve from simpler species (cheese! crossing the creationists again.)

You're thinking of ontology (development of the individual embryo) and philogeny (evolution of the species). There was a nineteenth century belief that "Ontogeny recapituates philogeny" which is what you are stating here, but it's false! Ontogeny does go through stages reminiscent of earlier forms, but each species does that in a slightly differnet way, and the stages that are displayed do not by any means include all the evolutionary stages. A human embryo spends some time looking a lot like a frog, but no time looking like a chimp.

Well we can watch a single cell become an organism. The idea is that the single cell retraces the steps that the species went through in evolving. First it is like an amoeba, then it is like a worm, then it is like a fish, then like a reptile, then like a mammal, and so on. It isn't a very exact process. Lots of the steps can be left out without losing anything, so eventually the genetic instructions for those steps are deleted.

And I needn't have worried, you got there on your own! (as usual). But what does this have to do with continuous creation? Continuous creation was a hot idea in the 1950s. It seemed to be refuted by the discovery of the microwave background, but with modern theories of "episodes" of inflation, however caused, the continuous creation idea might stage a comeback.

I am surprised to see a world class cosmologist asking this how and why question.

Suprised how? That a cosmologist would ask how and why questions?

Thanks for the conversation.

Thank YOU!

nightcleaner · Mar 28, 2005

Hi selfAdjoint

You are correct, and have new information for me, both much appreciated. I am pleased that there are ideas out there about what the universe might have looked like before there was time to look, or anything to look at. How entertaining. I would certainly like to know more about these ideas.

"The second question is: How (and why!) was the universe created and what happened before the big bang?" Marcus posted this sentance, a quote from Padmanabhan I believe.

I was trying to point out that there are some assumptions here. If the universe is said to be created, then one must assume that the speaker invokes some person or principle as a creator. I do not personally treat the idea of a creator as an assumption. Within my internal cosmology, the creator holds an honored and beloved position, but I wouldn't presume to insist anyone else require this belief. And I do not appeal to my belief, either, in trying to understand the universe. Laplace had some wrong ideas about inheritance of traits but was right, I think, in leaving the creator out of human attempts at understanding. "Because God made it that way, now go to sleep," was not a comfort to me, but a source of insomnia.

Philogeny. How embarassing. I knew I should have googled that up.

Yes, it is a flawed idea, in biology, for the reasons you mention, and others. I was just putting it up here for wallpaper, and maybe as a little friendly tickle for the creationists. Flawed as the idea is, it has value in understanding how things are done in biological evolution. The idea I am more interested in today is that conditions and events in the first instants of the big bang may be recapitulated on a microscopic scale all around us.

Long, long ago, far, far away, and very, very tiny. Irresistable.

The truth is I am still not comfortable with the expansion implied by gravity. The evidence seems irrefutable. But the windows on this elevator are all painted shut. My monkey and his gramma are never, ever going to accept that we have been accelerating all this time, and still can't tell we are going anywhere. How fast are we going now anyway? Four and a half billion years at one G...I refuse to calculate it. It wouldn't make any sense anyway.

Ok, Marcus Help! I am being kidnapped by logic. Four and a half billion c! No. That is just plain silly. And people argue about phase shift!

We are huge and expanding much faster than can possibly make any sense. Hence, the past is a tiny little homunculus hidden deep within us. We are expanding so fast that no ordinary perceived velocity will ever allow us to escape ourselves. We each of us carry the entire history of the universe in our bowels. What a concept.

So, if we look at things that are very very tiny, we should see our own universe as it was very, very long ago.

I have to tell the truth, it is a curse and I know I would be better off to keep my mouth shut. Here it is. It is easier to believe in an old guy with a long white beard, a bathrobe, and a magic finger than to accept this bill of lading for a load of manure. What does an optimist do with a load of crap except make fertilizer?

Anyway the idea should totally be falsifiable. All we have to do is compare very tiny stuff with very old stuff. If the two don't look the same, bingo.

For example: Very early universe, very high energy. Very small scale, very high energy. So far so good.

Darn, I wish I could find my copy of "The First Three Minutes."

Any help here? Anyone?

Inside the atom: gravity, then strong force, then weak force, then em. Is this like, inflation, quarkonium, neutronium, and let there be light? What was that about the ultraviolet catastrophe? I really have to find that book. I can see the cover: Stephen Hawking, grinning like the cover of Mad Magazine.

Heck with it. I am going to go get another copy.

Be well,

Richard.

selfAdjoint · Mar 28, 2005

nightcleaner said:

Hi selfAdjoint

You are correct, and have new information for me, both much appreciated. I am pleased that there are ideas out there about what the universe might have looked like before there was time to look, or anything to look at. How entertaining. I would certainly like to know more about these ideas.

The most mature paper on causal triangulations, is Ambjorn, Jurkievich, and Loll, which has received a lot of attention from the physics community. Marcus has linked to it a couple of time, as have I. The "Why" question seems to presume causality if nothing else ("Why? Because!"). To me, this doesn't require a mind, since causality is expressed as geometry in relativity ("Light-cones"). This is the attitude of the AJL paper.

"The second question is: How (and why!) was the universe created and what happened before the big bang?" Marcus posted this sentance, a quote from Padmanabhan I believe.

AAH! Light dawns. My apologies!

I was trying to point out that there are some assumptions here. If the universe is said to be created, then one must assume that the speaker invokes some person or principle as a creator. I do not personally treat the idea of a creator as an assumption. Within my internal cosmology, the creator holds an honored and beloved position, but I wouldn't presume to insist anyone else require this belief. And I do not appeal to my belief, either, in trying to understand the universe. Laplace had some wrong ideas about inheritance of traits but was right, I think, in leaving the creator out of human attempts at understanding. "Because God made it that way, now go to sleep," was not a comfort to me, but a source of insomnia.

It was Lamarck who taught inheritance of acquired traits. This seems like an awfully snotty comment of mine, but I have all these useless facts in my head!

Philogeny. How embarassing. I knew I should have googled that up.

What's in a name? You had the concept right on.

Yes, it is a flawed idea, in biology, for the reasons you mention, and others. I was just putting it up here for wallpaper, and maybe as a little friendly tickle for the creationists. Flawed as the idea is, it has value in understanding how things are done in biological evolution. The idea I am more interested in today is that conditions and events in the first instants of the big bang may be recapitulated on a microscopic scale all around us.

Marcus will tell you that Bojowald's LQG cosmology takes the universe back through the BB to the other side, where it has an "arithmetically negaive" mirror development. So in a sense in this approach it comes in from negative infinity (of age-of-universe, a simpler thing than time), does a minimal volume flip at BB time, and goes off to positive infinity. So the physicists are actively working on these concepts; the string folks have their clashing brane models too. Google on ekpyrotic for some of those. The name means "from the pyre" a reference to the myth of the phoenix.

nightcleaner · Mar 28, 2005

Rats! I am going to have to quit relying on this old creaky memory entirely. Lamarck indeed. Well a mark is a place, isn't it. I suppose the nursery rhyme about three blind mice and a farmer's wife has nothing to do with either of them, too. Humpf.

Anyway I edited my last post while you were adding your last post. Honestly I checked before I started and you were offline then. I really am going to go get that Hawking book.

Thanks,

Richard

ps that would be Stephan Weinberg. The Hawking book, of course, is A Brief History. I have had both volumes, but neither is on my bookshelf tonight. Instead, I came home with The Cambridge Handbook of Physics Formulas. Pure heroin for physics junkies.

nc

marcus · Mar 29, 2005

nightcleaner said:

... but neither is on my bookshelf tonight. Instead, I came home with The Cambridge Handbook of Physics Formulas. Pure heroin for physics junkies.

I must say i started laughing out loud when I read that.

I didnt find Hawking "Brief" readable. My mother-in-law didnt either so she gave her copy to me thinking that I would. it has sat idle on the shelf ever since.

never looked at the Cambridge Handbook of Heroin for Physics Junkies,
could be great fun!

Have been enjoying your conversation with spicerack. Now I regret having butted in. It was better talk when it was just you and her

marcus · Mar 29, 2005

selfAdjoint said:

Well, honestly, nightcleaner, if you assume a creator you're going to get static from those who, like Laplace, have no need for that assumption.
...

some people are proud of their parentage
some of their name
some of the clothes they wear
some of belonging to a good country club
I can't help being proud of living in a culture, or at least marginally on the outskirts of a culture, in which Laplace said that thing to Napoleon.

has anyone seen the movie "Russian Ark" by the way?
the french aristocrat who goes with you through the Tsar winter palace
impressed me as a neat guy.

I found some stuff on web that suggests that he presented his celestial mechanics to napoleon (whom he had taught at the royal artillery college) around 1805 (the publication date for volume 4) and napoleon afterwards remarked that he had found no mention of god in the whole multivolume work. so we are talking about a bon mot that is just about 200 years back.

marcus · Mar 29, 2005

people give different versions the most common one in those i found being

"Sire, je n'avais pas besoin de cette hypothèse."

and some give the date 1799 when the first two volumes of the set were published, but it was pointed out that napoleon was in Egypt that year, so Laplace could not have presented the work then. and it is suggested that he presented it in 1805, when the fourth volume was published.

then, it is said, Napoleon remarked that in all the work on celestial mech he could find no mention of god, and Laplace replied
"Sire, i had no need of that hypothesis."

nightcleaner · Mar 29, 2005

"Have been enjoying your conversation with spicerack. Now I regret having butted in. It was better talk when it was just you and her"

Nonsense, Marcus, and it is I who must apologise for having stolen your wonderful thread here for my own personal vehicle.

I remember enjoying reading the Hawking book, but then there do seem to be some things which I don't remember very well at all, and more worrisome, some things that never happened that I seem to remember quite clearly. On the other hand, I do remember looking at the Bojowald papers you have linked, and am ashamed to say that I never understood a word. I do like the idea of an inverse big bang, and would never have figured out that it was in there. Thank you. And the AJL papers also?

Well the inversion thing comes out negative in the exponent. I could quibble that it is not an arithmetic expansion, but an exponential one? Again, the bounce is not really a bounce, is it? Not even an inflection, altho it looks like it would be from where we are standing. More like the geometric progression of the horizon than like hitting a wall.

Running along the hyperbolic x-axis the tanhx comes up smoothly from below approaching the origin, and the sine adds a little lift to counter the upward slope so we don't really have to work to climb it. Then the coshx swoops down to push us along and keep us from the steep slope to infinity that follows along the sinhx, making for easy peddling in the first quadrent. No bounce. Contrast this with the sinx and cosx, where it is all up and down hill. You have to have energy to cross that first ridge, and then you have to do it again and again. Luckily you can save some energy on the downslope to use on the way up the next hill. That saved, or recovered energy is the bounce part. It isn't required in the hyperbolic transition along x, which, I suppose, is the one that better fits the big bang as a horizon problem.

I have a horrible feeling we are all going to regret my trip to the bookstore to find "The First Three Minutes" by Stephan Hawking. And did you know, by synchronicity I swear, that our Paddy has also written a book called by the same title? I was amazed when I googled it that there were three pages of sponsored hits on the phrase. And, again, when on about page ten I realized that many of the hits, even maybe most of them, had to do with organized sports! I was flabberghasted.

Who would ever have thought that sports writers, coaches, inspirational speakers, and creationists would be so impressed with a book by an astrophysicist.

nc

marcus · Mar 30, 2005

marcus said:

people give different versions the most common one in those i found being

"Sire, je n'avais pas besoin de cette hypothèse."

and some give the date 1799 when the first two volumes of the set were published, but it was pointed out that napoleon was in Egypt that year, so Laplace could not have presented the work then. and it is suggested that he presented it in 1805, when the fourth volume was published.

then, it is said, Napoleon remarked that in all the work on celestial mech he could find no mention of god, and Laplace replied
"Sire, i had no need of that hypothesis."

How did we get started talking about Hawking in the same breath with Laplace?
I experience a slight embarrassment when hawking is mentioned because of the disproportion between his stature as a scientist and as a figure in the public imagination.

You mentioned the book called The First Three Minutes. Was that not written in 1977 by Weinberg?

You might think Weinberg's book is out of date. But it is not so SPECULATIVE as hawking's popular writings. So Weinberg's book may well be on many people's shelf long after Hawking popular books are in landfill.

That doesn't mean there is anything wrong with speculation, just that it gets old faster than more factual substantive stuff.

and goodness knows, in science and cosmology in particular, even the FACTUAL stuff gets old pretty fast.

it is impressive that Steven Weinberg could write a book in 1977 that peoplel still want to read. he is a pretty impressive guy actually.

marcus · Apr 1, 2005

this morning went out in the garden and stood a while in a patch of bright sunlight by the apple tree, which is blossoming now (I tickled it with a feather yesterday apprehensive that bees might not come) and today there was a large black and yellow going around the apple flowers so things are working OK in that regard

I was feeling the solar constant 6E-117 and getting the warmth all the way into my bones---indoors it was cold---and thinking about the 14 psi pressure in the garden where psi is my jargon for E-107 natural units of pressure.

there were dewdrops on the leaves and they would have evaporated except for the 14 psi pressure (I mean 14E-107 natural)
so although I can't feel the pressure I can see the evidence. A pretty woman walked by the garden gate outside on the lane. She would be freeze-dried without this pressure. The leaves and I would be freezedried. We are all mostly moisture and other volatile liquids.

So I realized that part of the time when I'm out in the garden am am being appreciative of some basic quantities----the power per unit area of the sunlight, the force per unit area of the atmosphere, the temperature (E-29 natural at that hour of the day). I can say that I am glad those quantities are what they are, really glad, and if there were something to thank, I would give thanks, but since there isn't, I dont.

marcus · Apr 1, 2005

I was reading an article yesterday by a Madrid physicist Enrique Alvarez who has been, at least in former years, a string theorist. Now he seems
to be getting more interested in non-string quantum gravity and right in the middle of his paper I saw him define the Planck length with an 8pi.

It has been that way in most of the papers I've read recently whether by Bojowald, Padmanabhan, Alvarez. they don't apologize or remark on it. they just define the natural units the way like in this thread, with
|hbar|=|c|=|8piG|=1, and don't bat an eyelash.

this is more the way Kea said to go, forget that the Planck units were ever defined differently with |hbar|=|c|=|G|=1, and still appear that way in many a conventional textbook and handbook.

nightcleaner · Apr 1, 2005

Marcus
I respect your view, of course, and wouldn't dream of tickling your philosophical makeup, but...

Why is it not ok to thank a rock?

Thanks for being...

nc

marcus · Apr 1, 2005

nightcleaner said:

Marcus
I respect your view, of course, and wouldn't dream of tickling your philosophical makeup, but...

Why is it not ok to thank a rock?

Thanks for being...

nc

hey, good idea nightcleaner!
it just hadnt occurred to me.
you earn your keep around here

nightcleaner · Apr 1, 2005

Marcus, I don't know if i have ever asked you for your evaluation of quantum consciousness and the idea of a self-organizing computational automaton universe.

Of course i do feel grateful for the rocks or else what would we have to stand upon? Not to mention the trees, the flowers, even the feathers of the birds that waft the seeds into being. The sheer detail of the phenomena around us is overwhelming once you get started on it. And shouldn't one be grateful for the beauty of the orbitals?

marcus · Apr 1, 2005

nightcleaner said:

Marcus, I don't know if i have ever asked you for your evaluation of quantum consciousness and the idea of a self-organizing computational automaton universe.
...

you had better not ask me

I am a curmudgeon and set in my beliefs along these lines. I do not wish to elaborate on this. However I have a poetical streak. Here is a poem about rocks (and a hummingbird) which I seem to recall posting at PF before but forget when

Hummingbird Pauses by the Trumpet Vine
by Mary Oliver

Who doesn't love
roses, and who
doesn't love the lilies
of the black ponds

floating like flocks
of tiny swans,
and of course the flaming
trumpet vine

where the hummingbird comes
like a small green angel, to soak
his dark tongue
in happiness--

and who doesn't want
to live with the brisk
motors of his heart singing
like a Schubert,

and his eyes
working and working
like those days of rapture,
by van Gogh, in Arles?

Look! for most of the world
is waiting
or remembering--
most of the world is time

when we're not here,
not born yet, or died--
a slow fire
under the Earth with all

our dumb wild blind cousins
who also
can't even remember anymore
their own happiness--

Look! and then we will be
like the pale cool
stones, that last almost
forever.

marcus · Apr 1, 2005

I found the mary oliver poem on the web at
http://forwardmomentum.com/newsletter/forwardmomentum_news.htm
but it is also about 9/10 of the way down this page
https://www.physicsforums.com/archive/topic/t-27156_Greatest_Poem.html

nightcleaner · Apr 1, 2005

Beautiful, chilling.

Marcus, do you think it would be a good exercise to translate some of the formulations from my new Cambridge Handbook into the terms used in this thread?

nc

marcus · Apr 1, 2005

nightcleaner said:

do you think it would be a good exercise to translate some of the formulations from my new Cambridge Handbook into the terms used in this thread?

Let's start a new thread to examine the cambridge handbook of physics formulas.

I don't know the handbook. May I have the honor? I would like to see the table of contents. Unfortunately it would probably be a lot of work for you to copy the TOC and type it in here.

When you include Applied Physics, then physics is a huge topic (solid state, fluid mechanics, turbulence, acoustics, plasma physics, ye gods the list is endless)
I would really like to see what the menu is. maybe I can find it on Amazon where i can take a look at the TOC

[edit] richard, I found out all I could easily find out about the Cambridge Handbook. I think now that it is something for you to learn from, but that we probably wouldn't be able to use as grist for our mill in this thread. but you can try me out on some that you think are promising.
as a rule, if you see a formula with hbar, or c in it, or the electron charge e, or Boltzmann k, then calculation with that formula may be facilitated working in natural units[/edit]

nightcleaner · Apr 2, 2005

Ok Marcus.

Just like me to learn to build a paper airplane and then suggest we immediately start colonies on Mars. Oh well. I'll go play in the new thread. Thanks,
nc

marcus · Apr 3, 2005

Thing One about LQG

nightcleaner said:

...Just like me to learn to build a paper airplane and then suggest we immediately start colonies on Mars...

We are alike in that respect, except that I would prefer the colonies to be on the Jovian moon Callisto instead of Mars.

I was thinking lately about what would be Thing One to say about LQG, in a congenial company of nonspecialists.

It occurred to me that Thing Zero would be a quote from Einstein (Grundlage, 1916) that appears in Rovelli section 2.3.2

"The requirement of general covariance takes away from space and time the last remnant of physical objectivity."

General covariance is nowadays often called diffeomorphism invariance. Diffeomorphisms are smooth mooshings of a manifold, where smooth means infinitely differentiable. Our main goal should be to outwit the jargon and find the simple idea. Jargon is the dragon guarding the gate.

a manifold is a continuum (selfAdjoint says he likes that word better). a manifold is equipped with coordinate charts. If transposing from one chart to another is a smooth mapping then we say the manifold is smooth.

Every mathematical introduction to LQG begins the same with a compact smooth manifold M. The author will then usually say that for convenience we think of M as looking like the 3d sphere. But, it is understood, without the sphere's geometry. A limp shapeless "bag" of a 3d sphere.

So M is S³ but deprived of its native S³ metric geometry.

We have to begin with M as our idea of space because Einstein began his
"allgemeine Relativitaetstheorie" with such a manifold M, without a metric, and required above all that the system for finding a metric in harmony with substance should be unaltered by mooshing the manifold.

The two primal features whether of the classical or quantum theory are background independence (which means NO PRIOR METRIC) and diffeomorphism invariance (which means MOOSHING DOESNT MATTER)

And well somewhere in the first paragraph they toss in a 4d manifold you can think of as R x M, and you can assume that the same applies to it:

1. no prior metric
2. mooshing mox nix (Der Musherei macht nichts bei der Mannigfaltigkeit!)

now something cruelly unexpected is going to happen

an idea which kindly old father Newton gave us of a space that is independent of material substance, this space, as a separate entity existing of its own accord, is going to go poof

all that will be left is the Geometry that was on the space

as the smile on the cat's face remains after the cat vanishes

Using the force constant in equations

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