What If Missing Particles and Stuff Cannot Be Found?

[ohwilleke]

In fog for example?

Garth

A brilliant analogy, and arguably one applicable now.

 

[wolram]

Nice to see this thread still active, i started it because i think astro phys
is in the doldrums, may be i am wrong, which is not unusual, but it seems
to me that the main stream view is some what out of explanations, and
looks to some outlandish reasons why.
It could be that a eureka moment is just around the corner but i won't
hold my breath.

 

[SpaceTiger]

i started it because i think astro phys
is in the doldrums

Astrophysics is in its prime. With cosmology, we're only just now figuring out the basic parameters of the universe. At the same time, a revolution is going in our galaxy, as we're discovering the first planets outside of the solar system. If anything, the field is progressing too fast for the small contingent of astrophysical theoretists to keep up. Professors in the physics department here are nudging their students towards astrophysics because of all the opportunities available, while things like particle physics are being discouraged.

I don't know if we're about to have a "eureka", but there is sure to be lots of excitement in the field in the next 10 - 20 years.

 

[wolram]

Space Tiger.
Astrophysics is in its prime. With cosmology, we're only just now figuring out the basic parameters of the universe. At the same time, a revolution is going in our galaxy, as we're discovering the first planets outside of the solar system. If anything, the field is progressing too fast for the small contingent of astrophysical theoretists to keep up. Professors in the physics department here are nudging their students towards astrophysics because of all the opportunities available, while things like particle physics are being discouraged.
-----------------------------------------------------------------
It gives me a warm feeling that people are being nudged toward astro phys,
also a feeling of envy, just think you may discover some new **********
that explains the U, What is the state of funding these days?

 

[SpaceTiger]

What is the state of funding these days?

Eh, not so good. The problem is that our field is mainly the pursuit of "pure knowledge", so we can't really make money for anyone or contribute to political dominance. The budget juggling at NASA has been particularly problematic because our missions keep getting cancelled.

 

[wolram]

Maybe we should start a PFs collection

 

[Billy T]

Eh, not so good. The problem is that our field is mainly the pursuit of "pure knowledge", so we can't really make money for anyone or contribute to political dominance. The budget juggling at NASA has been particularly problematic because our missions keep getting cancelled.

I would be glad to donate the proceeds from my book, but unfortunately I always tell how to read it for free so after deducting the expenses, the proceeds are negative! Perhaps you should borrow a page form it and try to scare people into doing more for astro physics. - i.e. make them worry about really possible (if improbable) astro disasters and / or enjoy astro delights.

One encouraging thing to note on this last idea is that some wonderful Hubble photos are in todays newspaper (even here in Sao Paulo!) - that may help get funding for Hubble's repair. The problem is same one I had. - How to get those that are not already interested, interested. In your case, especially the ones and groups with money. (I only wanted to get more science students.)

Percival Lowell was rich and interested in finding "planet X" so he built the observatory now named after him at Flagstaff AZ. Some how more of that money that is wasted on weapons, etc. needs to be put into pure research where at least it is not likely to do any harm. More beautiful space photos, like those in today's paper will help recruit science students too.

 

[wolram]

why does politics have to infringe on science, it is neither one nor the other
science should be divorced from politics, it may be advantageous to let a fight
b in politics, but in science every one should be united.

 

[Billy T]

why does politics have to infringe on science, it is neither one nor the other
science should be divorced from politics, it may be advantageous to let a fight
b in politics, but in science every one should be united.

the answer in a word is: MONEY.

But this reminds me of an old university joke - The university administrator was complaining to the physics dept director: "Every year you ask for more money! Why can't you be more like the math department. - All they ever ask for is paper, pencils and trash baskets, or better yet be like the philosophy department - they publish everything they write and don't even need the trash baskets."

 

[turbo]

why does politics have to infringe on science, it is neither one nor the other
science should be divorced from politics, it may be advantageous to let a fight
b in politics, but in science every one should be united.

In an ideal world, maybe everyone in science would be united and working toward a common goal, BUT there is the little matter of funding. Major sources of funding originate in the public sector. Scientists, or perhaps more properly, the directors and administrators of the programs the scientists work in, fight turf wars to establish their programs as "worthy" and obtain funding. They regard this funding as a limited resource that must be battled over, and the "concordance view" researchers tend to get the lion's share of the funding. They often can and do wield political leverage in pursuit of funding, bringing politics and ideology into the mix.

For example, stem cell research has shown some promise in combating diseases arising from genetic deficiencies and may perhaps help slow, halt, or even reverse neurological damage resulting from injuries or diseases. The US government is presently dominated by the Republican party, which is heavily indebted (politically) to right-wing Christian fundamentalists. These people usually link any discussion on stem-cell research to abortion, and some hold views that ANY viable human life at any stage of development (even extending to uncombined sperm and eggs) is exactly equivalent to a living breathing human. Under these circumstances, political pressures will make it nearly impossible for stem-cell researchers to gain public funding in the US. I do not bring this up to take one side or the other, or to inject any political view into the mix, but to illustrate that politics is a powerful force that can derail any scientific endeavor, no matter how lofty the goals. If scientists are unwilling or unable to sway the Luddites and the creationists, etc, we will continue to be hampered by their political influence. Has anybody noticed the nice new Hubble Telescope pictures being circulated these past few days? John Q. Public is being courted heavily to keep HST alive. I hope it works. HST can do things that no ground-based scope can do, and Webb can only compliment it, not replace it. Write to your representatives in Congress. A few thousand well-expressed letters, including letters to your local newspapers, can do more good than you may realize. Rant mode OFF.

 

[Chronos]

I think that you're mistaken, here. Specialization often leads to systemic myopia. A particle physicist trying to set detection limits on the Higgs Boson is probably not the person who is best equipped to describe a model of the Universe in which the Higgs Boson is unnecessary, although I must say that Rocky Kolb seems quite open-minded about such things.

Huh? Do you have a study in mind that supports your assertion that specialization often leads to systemic myopia? That sounds like an unsupported, sweeping generalization. I hear cowbells ringing.

Einstein's theories started out not as mathematical representations, but as thought experiments - just the kind of logical associations that most people today would dismiss as crackpot ideas.

Oh please, that is absurd.

 

[turbo]

Huh? Do you have a study in mind that supports your assertion that specialization often leads to systemic myopia? That sounds like an unsupported, sweeping generalization.

Do you need a peer-reviewed paper to convince you that overspecialization leads to systemic myopia? I urge you to look at the medical field for an equivalent example. Generalists are in terribly short supply, especially in rural areas where they are most needed. Specialists can make a ton of money, especially if they enter fields like ophtalmology, cardiology, neurology, etc, so specialists abound, and small towns cry out for competent family doctors.

Oh please, that is absurd.

You should read about Einstein a bit. His theories started as gedankenexperimenten (thought experiments), generally as a first step toward simplifying a problem or explaining something illogical under existing physics. The mathematical modeling came later. If you have any source that explains how Einstein was playing with math problems and stumbled across SR, GR, or the photoelectric effect, please post them here. That's not how he worked.

 

[Billy T]

...You should read about Einstein a bit. His theories started as gedankenexperimenten (thought experiments), generally as a first step toward simplifying a problem or explaining something illogical under existing physics. The mathematical modeling came later. If you have any source that explains how Einstein was playing with math problems and stumbled across SR, GR, or the photoelectric effect, please post them here. That's not how he worked.

I can't agree with Chronos that your statement is absurd, but it certainly is overly broad.

Einstein, like most of us, worked in various ways. For example his now little read, but very important, at least at the time(1905) paper on Brownian motion was (as I understand it) motivated by the following mystery.

The velocity of the Brownian motion became slower the more accurately you measured it. (as they though at the time about how you should measure accurately - i.e. use more time difference between start and stop times to reduce % error in measurements of time difference and displacment.) Yet the Brownian movement never stopped!

You also must realize that in 1905, the continuum theory of matter was much more widely accepted than the atomic concept - hard to believe now that five years olds speak of atoms, but back then few physicists thought atoms much more than a strange speculation. Assume a small one existed, why could you not cut it in half and make two even smaller ones? - surely the reason had only to due with how sharp you could make your knife.

Einstein not only exhibited that random motion would indeed slow down (the accumulated displacement being proportional to the square root of the time difference) but also predicted how the density gradient of pollen grains (Brown was a biologist) in the vertical direction of the fluid would vary if the motion was the result of random collisions with particles too small to be seen (what we now call atoms).

He was not very important yet so it took several years of difficult experimental work by a French team (sorry but can't recall their names) to experimentally confirm this predicted density variation. Only after the French results confirmed E's predictions, did the physics community beginning to think that atoms might be indivisible.

Not to be too long in this post, I also quickly note that the classical idea of "equal partition of energy" and fact that no shortest wavelength exists in Maxwell's EM equations, lead to what was called the "ultraviolet castrophy" - catastrophic failure of classic physics to explain the fall off of radiation coming from a small hole in an isothermal cavity (a practical version of a Black body, even today). Again as I understand it, Plank had the experimental curve that now bears his name, and was "playing around" with math tyring to see how it could be fit when he found he could do so by quantizing (for no gedankenexperimenten reasons) the number of radiation states. Certainly Einstein used the gedankenexperimenten appproch, but not it alone.

 

[wolram]

Have made an attemt to understand pop 111 stars, it seems to me that
if they exist, then there should not be any conditions in our universe that
is time dependant for these things to form, ie if solar mass is a limiting
factor now why would it be different at an earlier stage of the Us
formation, it seems to me that gravity is a constant that is beyond doubt.

 

[Billy T]

Have made an attemt to understand pop 111 stars, it seems to me that
if they exist, then there should not be any conditions in our universe that
is time dependant for these things to form, ie if solar mass is a limiting
factor now why would it be different at an earlier stage of the Us
formation, it seems to me that gravity is a constant that is beyond doubt.

Not sure I understand your question and others such as Spacetiger can give you more informed infro, but there are a few comments that may be helpful I can make:

When the first stars began to form, the universe volume was about 35 times smaller and of course no stars had converted hydrogen into other elements, so the gas clouds, when they had cooled enough to let gravity collect them into smaller subregions, converted their potential energy into velocity/thermal energy as the gas mutually fell down the potential well it was forming.

The temperature required for these masses (much larger that the sun by factor of approximately 100), which were assembling from only Hydrogen (and a little helium) to fuse the hydrogen was essentially the same as it is today and far above that required to ionize all the then existing atoms completely. Fully ionized material does not radiate well compared to the radiation form transitions between states of bound electrons.

These large stars ran thru their life cycles quickly compared to the sun. When they died most, if not all, left black holes behind but what is important for your question is the tremendous gravitational energy released by a large mass collapsing into a BH, not the BH itself. What I like to call "meganova" event, as contrasted to the supernovas of this latter stage of the universe, It blasted shock waves thru the outer parts of the dying star of such force that all the elements with greater atomic numbers than iron could form in the collisions of lesser element nuclei. (iron itself and lesser atomic number element nuclei were formed in successive fusing stages inside the star before the meganova event {and a little "trans iron" also but you can forget about it.})

The subsequent generations of stars thus could form from gas clouds that contained many different atomic number atoms, not all completely ionized a few thousand (?) years (or less) after the meganova event that formed them. As these later "want to be" stars began to condense into smaller space under their mutual gravity, intense radiation began to be emitted from those partially ionized atoms. This did not happen in the formation of first generation stars that were assembling only from hydrogen and helium to any comparable degree as these two element are much easier to full ionized than the "trans iron" elements with many electrons.

I caution you now that I am less sure about how it works in detail, but the general idea is that this radiation exerts a pressure on the more distant gas of the cloud that would otherwise have also fallen into the forming star, blowing it away. Consequently, the second and later generations stars, as you suggest have the same gravity acting, but counter balancing it is this radiation pressure that at some radius in some stage of the contraction exceeds the gravity. Both the gravity and radiation fall off as inverse square so this radius may not be too well defined, but the effect of it is to limit the total mass of the star that can form to much lower value than could form before these "trans iron" elements existed.

I hope ST, or others, better versed than I am, will correct my errors, but at least you now have the general picture and an answer to your questions. If you alread knew most of this, please take no offense - others who may know less may have benfited.

 

[SpaceTiger]

if solar mass is a limiting
factor now why would it be different at an earlier stage of the Us
formation, it seems to me that gravity is a constant that is beyond doubt.

Gravity is assumed to be constant, but as Billy T said, there would be fewer "metals" (elements heavier than helium) in the primordial gas. The reasons they expect this to lead to massive stars are fairly complicated, but can be summarized as follows:

1) The size of the star is determined by the scale on which the initial molecular cloud fragments. The initial molecular clouds will be composed only of H₂, so the scale on which they fragment will be determined by the properties of this molecule. This molecule is a less effective coolant than, for example, CO, so the cloud will fragment on a larger scale. This leads to more massive stars.
2) Once the stars are formed, their opacities (their tendency to absorb radiation) are decreased by the fact that dust can't be formed in the atmosphere. Decreased opacity means decreased mass loss (as in stellar winds), which means that the star can maintain its initially large mass.

There is still some debate as to whether all Pop III stars must be massive. This is important because subsolar mass Pop III stars would still be around in the present day. If no such stars are formed, it would be no surprise that we don't observe them in the local universe.

 

[Chronos]

There are no pop III stars around today because the ISM is heavily polluted with metals. We need to work on that problem first.

 

[wolram]

Thanks for replies, BILLY T, SPACE TIGER.

Sorry to jump around from subject to subject, but the existence of
magnetic monopoles was mentioned, if anyone wants to flick through
a few papers try this.
http://www.google.co.uk/search?hl=en&lr=&q=+site:arxiv.org+magnetic+monopoles+2005

 

[wolram]

There are no pop III stars around today because the ISM is heavily polluted with metals. We need to work on that problem first.

Another difficult problem Chronos, this paper is 81 pages and recent
http://xxx.lanl.gov/PS_cache/astro-ph/pdf/0504/0504193.pdf

It seems that galactocentric distance could be more important than
age for metal abundances.

 

[Chronos]

Agreed. That is a good read. It took some time to load and read [I'm on dial up]. Thanks for that one. I like your references, they are solid.

 

[turbo]

Another difficult problem Chronos, this paper is 81 pages and recent
http://xxx.lanl.gov/PS_cache/astro-ph/pdf/0504/0504193.pdf

It seems that galactocentric distance could be more important than
age for metal abundances.

I've posted this before. The authors found no reduction in galactic metallicity with age back to z~6.5. Did proposed Pop III stars all live and die in the first couple of hundred Myears since recombination?

http://cosmos.as.arizona.edu/~thompson/pubdb/docs/barth03a.pdf

 

[turbo]

You should read about Einstein a bit. His theories started as gedankenexperimenten (thought experiments), generally as a first step toward simplifying a problem or explaining something illogical under existing physics. The mathematical modeling came later. If you have any source that explains how Einstein was playing with math problems and stumbled across SR, GR, or the photoelectric effect, please post them here. That's not how he worked.

I did not have this citation handy yesterday, and am including it now for those who would like a little insight into Einstein's methods. He had the thought experiments for GR solidified a few years after publishing SR, but it took him almost a decade, and a lot of help to come up with a mathematical model for GR that could make accurate predictions.

http://xxx.lanl.gov/PS_cache/physics/pdf/0504/0504179.pdf

 

[wolram]

http://uk.arxiv.org/abs/astro-ph/0502385

Authors: Laurence Eyles (1), Andrew Bunker (1), Elizabeth Stanway (2), Mark Lacy (3), Richard Ellis (4), Michelle Doherty (5) ((1) University of Exeter, (2) University of Wisconsin-Madison, (3) Spitzer Science Center, (4) Caltech Astronomy (5) Institute of Astronomy, Cambridge)
Comments: Submitted to MNRAS

We present new evidence for mature stellar populations with ages >100Myr in massive galaxies (M_stellar>10^10M_sun) seen at a time when the Universe was less than 1Gyr old. We analyse the prominent detections of two z~6 star-forming galaxies (SBM03#1 & #3) made at wavelengths corresponding to the rest-frame optical using the IRAC camera onboard the Spitzer Space Telescope. We had previously identified these galaxies in HST/ACS GOODS images of Chandra Deep Field South through the "i-drop" Lyman break technique, and subsequently confirmed spectroscopically with the Keck telescope. The new Spitzer photometry reveals significant Balmer/4000Ang discontinuities, indicative of dominant stellar populations with ages >100Myr. Fitting a range of population synthesis models to the HST/Spitzer photometry yields ages of 250-650Myr and implied formation redshifts z~7.5-13.5 in presently-accepted world models. Remarkably, our sources have best-fit stellar masses of $2-4x10^10M_sun (95% confidence) assuming a Salpeter initial mass function. This indicates that at least some galaxies with stellar masses >20% of those of a present-day L* galaxy had already assembled within the first Gyr after the Big Bang. We also deduce that the past average star formation rate must be comparable to the current observed rate (SFR_UV~5-30M_sun/yr), suggesting that there may have been more vigorous episodes of star formation in such systems at higher redshifts. Although a small sample, limited primarily by Spitzer's detection efficiency, our result lends support to the hypothesis advocated in our earlier analyses of the Ultra Deep Field and GOODS HST/ACS data. The declining global star formation density and presence of established systems at z~6 suggests long-lived sources at earlier epochs (z>7) played a key role in reionizing the Universe.

 

[wolram]

The age of our universe 13.7Gys ,seems to force us to believe that
early stars had a short life, i am not sure if 1Gy is long enough for
the first stars to form, i would have thought that the gasses would
be to hot and chaotic at this time, but i am sure some one has a
model that works.

 

[wolram]

A space time map of the universe

http://www.people.cornell.edu/pages/jag8/spacetxt.html .

Reading cosmology often leaves me wishing I had a simple map of the Cosmos for reference and orientation, just as I want a globe handy when reading the geography or history of Earth. As I have never found a suitable map for this purpose, however, I decided to attempt its production myself, proceeding on the generally held assumption that the Universe has expanded to its present size from very small beginnings. The resulting map is therefore relevant to either "Big Bang" or "Inflationary" cosmology. I found the mapping effort so illuminating and mind-stretching that I feel others interested in cosmology and astronomy generally will find the map and mental exercise it affords both stimulating and useful.

 

[wstevenbrown]

This is a very entertaining thread. One of the ideas only very briefly mentioned was Primordial Black Holes. I'd like to expound a bit. The upper limit for the mass-equivalence of a PBH is established by WMAP CMB data, and by the horizon problem-- PBH's that are too 'massive' scission off and form their own universes, forever separate from ours. To figure out the power spectrum of the PBH's at the time of their formation, just run their accretion history backwards for 13.7 BY. Simple, right?

Actually not. We know that the really big ones are detectable by their gravitation and by the polar jets of their accretion disks, if they are 'feeding'. It isn't too big a stretch to imagine that mass increase by accretion has always exceeded mass decrease by Hawking radiation. I do not suggest that dark matter lies in this size regime-- it's been pretty well accounted for. What I am suggesting is that their may be a very large population of subJovian PBH's whose accretion history is more... ambiguous. In the range from Jupiter-mass to Lunar-mass, there is a cutoff below which Hawking Radiation predominated, and above which accretion predominated. Those which survived, grew, and became the population we have identified and catalogued today-- at least those upwards of 1.5 MSols.

The population of below lunar-mass is usually dismissed as having already evaporated by HR by now. This takes some careful thinking, tho. What if there are stable 'plateaus' which prevent further decay? Consider-- the SUSY particles we have been thinking about range in mass from a medium-sized molecule to a pony. Might there not be other particles higher in mass, neutral, weak-or-non-interacting, in addition? Theory doesn't usually consider such particles, as they cannot be constructed in the modern universe by bottom-up methods. OTOH, the BB had the energy of the entire cosmos at its disposal for top-down formation.

How is this lunacy falsifiable? Easy. Each mass range has a characteristic 'temperature' based on its formation epoch-- when it was just cool enough to allow formation, but not hot enough to cause destruction of the particle in question. This implies a characteristic kinetic energy, on average. With respect to some particular massive object, this implies a very narrow range of orbit sizes, and therefore, a characteristic density profile. DM halos should have identical density characteristics WRT the original baryonic mass of the galaxy.

Okay, I slipped in a Joker there-- those facile conclusions follow only if all DM is one particle type. But. It's only a little bit hairier math with a spectrum of particles. And we have access to a large part of the spectrum (the lower part) by examination of TeV, PeV, and EeV cosmic rays and their decay products. My point being that an understanding of the lower part of the power spectrum will enable (sensible)extrapolation higher up.

Set my maunderings aside for the moment. Here are a couple of papers which consider the constraints on the PBH mass spectrum:

arxiv.org/astro-ph/0504606
arxiv.org/astro-ph/0504034
arxiv.org/astro-ph/0410359

Have fun! Steve

 

[wolram]

http://en.wikipedia.org/wiki/Status_of_special_relativity

Special relativity is not compatible with the physical existence of the following objects, forces, or laws (except in the nonrelativistic limit in which all speeds are much less than c):

1. Infinitely rigid rods, or any other object which transmits forces at infinite speeds. Note that this would require the existence of a new force which is not currently explained by any of the laws of physics.
2. Tachyon particles, unless these particles cannot transmit any information at superluminal speeds, or are somehow not subject to the laws of cause and effect.
3. Rulers which are immune to Lorentz contraction. Again, this would require a new force not currently explained by the laws of physics.
4. Devices which can record absolute position. Note that the existence of such devices would also contradict Galilean relativity.
5. Clocks that are immune to time dilation. Again, this would require a new force not currently explained by the laws of physics.
6. Clocks which can record absolute time. Indeed, the concept of absolute time is philosophically inconsistent with Einstein's interpretation of special relativity.
7. Forces which can act instantaneously at a distance; this includes Newton's law of gravity and Coulomb's law of electrostatics. Note however that these two laws can be modified (to general relativity and Maxwell's equations respectively) in a manner consistent with or generalizing the theory of special relativity. There are also some laws of physics which act non-locally but do not transmit information at superluminal speeds, and which are thus technically (if not philosophically) consistent with special relativity; the primary example here is the collapse of the wave function.
8. Laws of nature which are Galilean invariant instead of Lorentz invariant, or which are not invariant under either of these two transformations.
9. The Newtonian velocity addition law v = v1 + v2; this law is replaced by the relativistic addition law.
10. The Newtonian linear relationship p = mv between momentum and velocity, and the Newtonian quadratic relationship E = \begin{matrix}\frac{1}{2}\end{matrix} mv^2 between kinetic energy and velocity. These should be replaced by the equations p = Ev / c2 and E2 = m2c4 + p2c2. Similarly, Newton's second law in the form F = ma is no longer valid, but must be replaced by F = dp / dt (which is in fact closer to Newton's original formulation of this law).
11. The Schrodinger equation, which is the quantization of non-relativistic equation E = p2 / 2m + V from Newtonian mechanics. This can be replaced by the Dirac equation, Klein-Gordon equation, or quantum field theory.
12. Nonrelativistic fluid equations such as the Euler equations and Navier-Stokes equations; these must be replaced by relativistic fluid equations such as the Relativistic Euler equations.
13. Additivity of mass; the total mass of a system (as determined by solving the equation E2 = m2c4 + p2c2, where E is the total energy and p is the total momentum) is not necessarily equal to the sum of the masses of its components, just as the length of a sum of vectors is not necessarily equal to the sum of the lengths of the individual vectors. Indeed there is a triangle inequality which says that the total mass is always greater than or equal to the sum of the individual masses. However, the total mass of a system remains conserved (this is a consequence of conservation of energy and momentum).
14. Conservation of particle number is compatible with relativity, but once quantum mechanics is also added, it is possible that this conservation law breaks down, leading to spontaneous particle creation and annihilation. This phenomenon is usually studied within the framework of quantum field theory.
15. Wormholes or other objects which affect the topology of spacetime. However, these objects can be compatible with general relativity.

 

[wolram]

Welcome to the thread Wstevenbrown

 

[wolram]

The population of below lunar-mass is usually dismissed as having already evaporated by HR by now. This takes some careful thinking, tho. What if there are stable 'plateaus' which prevent further decay? Consider-- the SUSY particles we have been thinking about range in mass from a medium-sized molecule to a pony. Might there not be other particles higher in mass, neutral, weak-or-non-interacting, in addition? Theory doesn't usually consider such particles, as they cannot be constructed in the modern universe by bottom-up methods. OTOH, the BB had the energy of the entire cosmos at its disposal for top-down formation.
--------------------------------------------------------------------------
Hawking radiation is one of my pet hates as AFAIK it can only be verified
at short range from BH.
As for new particles why not, i prefer a theory that does not include
undetectable particles, "or hard to falsify", but to deny the possibility is
foolish.

 

[wolram]

http://www.lns.cornell.edu/spr/2003-06/msg0051723.html

In article <3edac15e.18945141@news.charter.net>,
Lucius Chiaraviglio <luciusone@chapter.net> wrote:

>baez@galaxy.ucr.edu (John Baez) wrote:

>> [. . .] the Hawking radiation for a solar-mass
>>black hole has a temperature of 10^{-8} kelvin. This is 300
>>million times colder than the microwave background radiation,
>>not to mention the heat generated by bits of gas that tend to fall
>>into black holes. Indeed, as of 1994, the coldest temperature ever
>>achieved in the lab was 7 x 10^{-7} kelvin - seventy times hotter than
>>this. So even if we tried as hard as we can, we'd have serious
>>trouble making thermal radiation as hard to detect as the Hawking
>>radiation produced by a real-world black hole!

>ONLY a factor of 70? This suggests that by the time we could
>actually get a probe out near to a stellar-mass black hole, we might
>well be able to build a detector able to sense the Hawking radiation
>from it. Of course, this would only work if the black hole didn't
>have stuff falling into it. I wonder if the luminosity of radiation
>produced by infalling interstellar medium (assuming a black hole
>not close to any other stars) would be low enough at the relevant
>wavelengths to permit detection?

I doubt it. But, having gotten to the black hole, maybe our
high-tech future friends can build some sort of shield around it
and isolate it for experimental work. All sorts of amazing
things will eventually be possible given enough time and hard
work. I was mainly talking about the extreme unlikelihood that
we'll detect Hawking radiation from solar-mass or heavier black
holes using current astronomical methods.

Only black holes of mass less than about 10^{11} kilograms - the mass
of a mountain on Earth - would radiate away a significant fraction
of their mass over the lifetime of the universe. So far, there's no
evidence that such black holes exist.

 

[Billy T]

...reasons they {metals} ... lead to massive stars are ... :
1) The size of the star is determined by the scale on which the initial molecular cloud fragments. The initial molecular clouds will be composed only of H₂, so the scale on which they fragment will be determined by the properties of this molecule. This molecule is a less effective coolant than, for example, CO, so the cloud will fragment on a larger scale. This leads to more massive stars.

I certainly am not going to dispute with you in the space physics field, but I do know a little about spectral radiation, absorption, etc.
Both H2 & CO are linear molecules with simular possibilities for rotational and vibrational IR radiation cooling (when excited) but of course their frequencies are different and CO, being asymmetric, probably has a more complex "band" structure. (I put "band" in quotes because I am guessing that at gas cloud densities, the individual IR lines may not overlap as they do in Earth's air, unless you are talking about temperatures high enough for Doppler to make them do so.)
I don't have any convenient access to both the (gen III ?) stellar continuum(?) or other radiation distribution sources the metals are immersed in and about their opacity when convoluted with this flux, or about inelastic colision rates (for production of excited states), but you may (probably do).
I would bet, that net radiation cooling comes from the fact that there are many more colisional excitations compared to number of stellar radiation absorptions that effectively heat, but I would also bet that the IR radiation from your metals is reabsorbed many times before it "walks" out of a large gas cloud.
If only collisions are significant, then different metal lines(bands?) will surely have come from different "optical depths" and the "cloud escaping photons" will thus come from different temperature regions within the cloud. (Must be a really messy problem to get all this right!)

However, and this is my question, I find it hard to believe (just by intuition) that this greater "metal" cooling effect which causes the latter generation stars form from smaller parts (your "scale on which they fragment") of the gas cloud containing "metals" is so overwhelming that the changing volume of the universe (and hence gas density in each cubic meter) can be neglected by compairsion. - Metals in quotes here as I never have liked astro physicists confusing the meaning of term "metal" the way you all do. - Most of us non astro physicists think that metals are a class of dense matter that have non bound electrons free to move (those above the Fermi surface, which can be at different energy levels for different directions in the crystal), but it is clearly to late for astrophysicists to adopt a new term.

Not challenging you. Just want to make sure that it is true physics and not simply something (gas cloud density change) you forgot to mention. I'll take your word on this, if it is true, that the changing density of the universe has only a minor effect in compairsion to the difference between H2 only and H2+Metal cooling in determining the typical star size.

I may have error in my reply to Wolram by focusing on the radiation pressure "blowing the gas away" that would normally have fallen into the gen III star. If I did please state this as an error or a if real, only minor effect. From your post, I infer that even if this is "blow away effect" is real, it is less important that the initial scale of the self gravitating collapse.

I am almost certain that you were only using CO as an example of many different metals. Is there some reason why you chose CO as your example of a metal? I.e. is it (and perhaps a few others) the only ones that are really significant. If yes, is this because they have absorption bands where the incident radiation is or if there is no significant incident radiation from assembling IR stars (ones not yet nearly hot enough for fusion) because they have unusually high inelastic collision rates? - I can't see why the inelastic excitation of CO would be much higher than for H2, and certainly H2 is still the dominate collider. I.e. I still don't have a clear understanding of this.

2) Once the stars are formed, their opacities (their tendency to absorb radiation) are decreased by the fact that dust can't be formed in the atmosphere. Decreased opacity means decreased mass loss (as in stellar winds), which means that the star can maintain its initially large mass. ...

I did not entirely follow your here, in part because I am not clear about which stars (your third word) you are speaking of (Gen III or latter ones). I never have been clear on where "cosmic dust" comes from, so you comment "dust can't be formed in the atmosphere" gives me some ideas and problems. I have always assumed that most "cosmic dust" was micro aggrates of many atoms and molecules. I have no idea how such an aggrate could even survive in a stellar atmosphere, much less form there. Could you clarify this for me (and others)?

 

[wolram]

http://www.math.columbia.edu/~woit/blog/archives/000168.html

an entertaining Chronical from NOT EVEN WRONG.

on String theory.

 

[wolram]

By BILLY T
(and hence gas density in each cubic meter) can be neglected by compairsion. - Metals in quotes here as I never have liked astro physicists confusing the meaning of term "metal" the way you all do. - Most of us non astro physicists think that metals are a class of dense matter that have non bound electrons free to move (those above the Fermi surface, which can be at different energy levels for different directions in the crystal), but it is clearly to late for astrophysicists to adopt a new term.

http://en.wikipedia.org/wiki/Metallicity


Metallicity
From Wikipedia, the free encyclopedia.

In astronomy, the metallicity of an object is the proportion of its matter made up of elements other than hydrogen and helium. All heavier elements are described in astronomy as metals.

The metallicity of an object can give an indication of its age. When the universe first formed, it consisted almost entirely of hydrogen and helium (with only trace amounts of lithium), and so the oldest stars have very low metallicities. As the age of the universe increases, so does its metal content, due to nucleosynthesis in stars, and the return of metal-enriched material to the interstellar medium (ISM) via planetary nebulae and supernovae.

The sun's metallicity is approximately 1.6 per cent by mass. For other stars in the galaxy, the metallicity is often expressed as [Fe/H], which represents the logarithm of the ratio of the star's iron abundance to that of the sun's.

Young Population I stars, (like the sun) have significantly higher metallicities than older Population II stars, which formed when there was a lower metal content in the universe. The very first stars, (referred to as Population III) are estimated to have a metallicity of <-6.0. Currently, no Population III stars have been found.

Across the galaxy, metallicity is higher in the centre and decreases moving outwards. This is because there are more stars in the centre of the galaxy and so over its lifetime, more metals have been returned to the ISM. Similarly, larger galaxies tend to have higher metallicities than smaller ones. In the case of the Magellanic Clouds, two small irregular galaxies orbiting the Milky Way, the Large Magellanic Cloud has a metallicity about 40 per cent of the galactic value, while the Small Magellanic Cloud has a metallicity about 10 per cent of the galactic value.

It is a confusing term but i hope this helps for anyone not in the know.

 

[SpaceTiger]

A space time map of the universe

I'm biased cause my roommate did it, but I'd say this is the best map of the universe:

http://www.astro.princeton.edu/~mjuric/universe/

 

[SpaceTiger]

Not challenging you. Just want to make sure that it is true physics and not simply something (gas cloud density change) you forgot to mention.

Although the average density of the universe does change with time, the density scales interior to highly non-linear perturbations (i.e. galaxies) are not set by the size of the universe. Instead, they're set by the physical mechanisms which halt their collapse. It's basically the same reason that our bodies are not expanding due to the Hubble Law -- there are much stronger forces governing our size.

I'll try to address your other points at some other time, as it will take a while to sort through and explain properly.

 

[wolram]

I'm biased cause my roommate did it, but I'd say this is the best map of the universe:

I quite agree please give your room mate my thanks.

 

[Billy T]

...I never have liked astro physicists confusing the meaning of term "metal" the way you all do. - Most of us non astro physicists think that metals are a class of dense matter that have non bound electrons free to move ..., but it is clearly too late for astrophysicists to adopt a new term.

...Currently, no Population III stars have been found.
...

Thanks for infro you supplied. I knew most of it already. According to my local newspaper's "science page" (a questionable source even before the original English got translated into Portugese) a gen III star may have recently been found.

I was only trying to object to the astrophysicists use of same word, metal, to refer to elements like oxygen, carbon, etc.

 

[Billy T]

...What I am suggesting is that their may be a very large population of subJovian PBH's whose accretion history is more... ambiguous. In the range from Jupiter-mass to Lunar-mass, there is a cutoff below which Hawking Radiation predominated, and above which accretion predominated. Those which survived, grew, and became the population we have identified and catalogued today-- at least those upwards of 1.5 MSols...Here are a couple of papers which consider the constraints on the {black hole} mass spectrum:
arxiv.org/astro-ph/0504606
arxiv.org/astro-ph/0504034
arxiv.org/astro-ph/0410359

I find your statement that there "may be a very large population" of early black holes that have now grown to "upwards of 1.5 MSols" black holes very interesting.
With much less knowledge than you obviously have, I postulated a dark mass of 2.2MSols was now approaching our solar system in a book I wrote, trying to attract more students, who are now totally uninterested in science, to become more interested in the sciences, by scaring (slight gravitationally induced change in Earth's orbit causes rapid onset ice age - Northern summers too cold to all melt prior winter's ice, etc.) them a little. (I'm a retired physics prof/ researcher.) All the physics in book is valid, but woven into a scary story, and perhaps not "very highly improbable" as I thought, if you are correct. Perhaps only "very improbable" but most cosmic disasters stories are "quite improbable."

In addition to a small black hole, I also discussed the possibility that this space visitor could be a very old neutron star. Stating that it might currently be undetectable at 130 AU in reflected sunlight, except by the largest telescopes that were all tied up working at high magnification on distant objects /regions of space, because (1) it was no longer a pulsar or (2) was one with residual magnetic now too weak or mag field too well aligned with the spin axis to make detectable EM radiation, and or (3) had axis pointed nearly transversely to its trajectory toward solar system. I noted in book that if it formed with mass just above the max mass for a dwarf, (1.4Msol) it could have grown by slow (did not want it to get detectable hot again) accretion of Hydrogen and "cosmic dust" to the postulated 2.2Msol. From what you say about BHs, this postulated mass gain seems reasonable.

I of course tried to read you mass distribution reference, but find I don't know how. They are not web pages and I don't recognize the journal, if that is what they are. Suggestion, comments please.

 

[wolram]

Billy T
a gen III star may have recently been found.

Do you have any more on this Billy T.

I was only trying to object to the astrophysicists use of same word, metal, to refer to elements like oxygen, carbon, etc.

I agree with you on that one.

 

[Billy T]

Billy T
a gen III star may have recently been found. Do you have any more on this? ...

Unfortunately no. It was just a few column inches in the now discarded main paper in Sao Paulo about 3 or 4 weeks ago. The essence of article was a star (or whole galaxy seems more likely to me) had been discovered at high red shift with low "metal" index. This Sao Paulo newspaper is IMHO one of the worlds best. - It should be they copy from all the major papers of the world, but the translators don't always understand the science articles well, so you must "correct" as you read. - I don't remember for sure, as age of universe has also been recently been in the paper - revised slightly down to 13.7 and that may be confused in my memory with this article, but I think the article said the "star" was 12 billion years old. That distance is what made me guess the "star" was really an entire galaxy of old gen III stars.

Also want to correct miss statement in my last post (#88):
wstevebrown's three references are web pages.
Reason for my error may interest you. In Sao Paulo, the phone system frequently saturated, but the company never admits this - You are informed that "the number does not exist" even if you single button speed dial it 100s of times successfully. Well my ISP appears to have done the same. Everyone here knows that the local internet system will not support all the Brazilian IRS filings that will come in today (last day to file) so it appeared to have saturated one day early. I think the ISP was telling everyone not trying to file their return that the webpage they wanted did not exist, to let the critical IRS returns get filled. (Just guessing) Sao Paulo is world's fourth largest city and surprisingly "plugged in" -still a lot of dial up modems though. I joined PF when I got DSL. For most people, internet filling is mandatory this year. It is middle of nite now and every thing is now OK.

 

[Chronos]

SpaceTiger is entirely correct. He is trying to be nice. I am not. Bad science is bad science and both of you guys should know better.

 

[wolram]

Sorry i have gone out of sync with the thread i lost connection to
PF while modifying post to Billy T.
The joys of the internet, can't live with it can't live without it seems
we all have problems from time to time Billy.

 

[wolram]

I guess it about time to let this thread slide into the archives, it has been
a revelation to me, and i thank every one who participated, i feel a little
let down that participation was not more diverse, but can understand the
constraints people work under.

 

[wolram]

Two new papers.




http://arxiv.org/PS_cache/hep-ex/pdf/0505/0505027.pdf
Title: Searches for the Higgs boson in Minimal Supersymmetric CP-conserving and CP-violating Standard Model scenarios at LEP
Authors: Pamela Ferrari
Comments: 4 pages, 4 figures

It is important to study extended models containing more than one physical Higgs boson in the spectrum. In particular, Two Higgs Doublet Models (2HDMs) are attractive extensions of the SM, predicting new phenomena with the fewest new parameters. The Higgs sector in the Minimal Supersymmetric extension of the SM (MSSM) is a 2HDM itself. The neutral Higgs searches performed at LEP are showing no evidence of the presence of a signal and have therefore been interpreted in the context of 2HDMs. Depending on the model considered exclusion of large regions of the parameter space can be obtained, but the existence of the lightest Higgs boson with masses lower than 90 GeV is not ruled out in all models by LEP. In the MSSM at least one of the neutral Higgs bosons is predicted to have its mass close to the electroweak energy scale; when radiative corrections are included, this mass should be less than about 140 GeV. This prediction provides a strong motivation for searches at present and future colliders.

 

[wolram]

http://arxiv.org/abs/astro-ph/0505237
Title: Results of a Search for Cold Flows of Dark Matter Axions
Authors: L. Duffy, P. Sikivie, D.B. Tanner, S. Asztalos, C. Hagmann, D. Kinion, L. J Rosenberg, K. van Bibber, D. Yu, R.F. Bradley
Comments: 5 pages, 3 figures

Theoretical arguments predict that the distribution of cold dark matter in spiral galaxies has peaks in velocity space associated with non-thermalized flows of dark matter particles. We searched for the corresponding peaks in the spectrum of microwave photons from axion to photon conversion in the cavity detector of dark matter axions. We found none and place limits on the density of any local flow of axions as a function of the flow velocity dispersion over the axion mass range 1.98 to 2.17 $\mu$eV.

 

[wolram]

This is a must read.

http://www.math.columbia.edu/~woit/blog/archives/000154.html

and this on Roger Penrose book The road to reality.

[URL]http://motls.blogspot.com/2005/02/frank-wilczek-about-penroses-new-book
.html[/url]

Seems i lied about letting this thread slip into the archives.

 

[turbo]

Hi, Wolram:

Here is a paper that might appeal to you. I have at this point only read portions of it (82 pages!), but it seems well-reasoned and well-presented.

http://xxx.lanl.gov/PS_cache/astro-ph/pdf/0505/0505266.pdf

 

[wolram]

Thanks Turbo.

Cosmic Strings have already been mentioned LMs blog site discusses a
recent sighting