Comment by L.P.
Forgive me for barging in here, but I don't get it.
A mass as great as the Sun's falling in from infinity to a point will develop a certain amount of energy as a result of the collapse. This energy is radiated away. Given a certain radiation rate and the total energy evolved, it doesn't sound all that difficult to arrive at an estimated total lifetime.
That estimate seems rather short compared to the geological record.
Whatever the radiation mechanism, it isn't creating energy. And so has little bearing on the thermonuclear fusion question.
Reply
Energy- and momentum conservation are direct consequences of Newton's laws and are therefore strictly applicable only in Classical Mechanics (
more).
The radiation produced as a result of inelastic atomic collisions is of a quantum mechanical nature and therefore not subject to the same conservation laws. The assumption that the intensity of the radiation emitted by an atomic transition is always constant (as implied by the Bohr-Einstein radiation formula) is therefore only hypothetical and will in general not be valid. Experimental evidence from measurements of the
solar - and
ionospheric Lyman- series emission indicates in fact that plasma field fluctuations strongly enhance the intensity over the 'energy conserving' level (this does of course not mean that the frequency changes but only the amplitude of the electromagnetic wave emitted by the atom, i.e. the Planck constant in the Bohr-Einstein Radiation formula becomes variable).
If you take this into account you will obviously arrive at a much longer value for the lifetime of the sun.
As indicated, this all does not necessarily rule out that nuclear fusion of the sun may nevertheless be significant.
However, the sharp definition of the sun proves that usual atomic collision processes cool the solar atmosphere (otherwise we would be looking at some fuzzy ball several times the size) and if you calculate the related radiative emission (bearing the above mentioned enhancement in mind), you will find that this is more than enough to account for the present intensity of the sun.
It is important to see however that these processes only take place in the solar atmosphere which is sufficiently diluted to allow complete atoms to exist (it is easy to show from the known values for the solar mass and radius that the bulk of the solar material is so dense that it consists of a 'soup' of protons and electrons which allows no radiative processes to take place).
Comment by Jeremy Carlo
Hrmmm,
1. well, the disparity in composition between Pop II and Pop I stars suggests that some sort of fusion is taking place SOMEWHERE in the universe. Remnants of stellar explosions are known to be rich in heavier elements. Could the fusion be in the center of stars, perhaps?
2. also, if nuclear fusion were taking place inside the Sun, we would detect neutrinos being emitted. In fact we do detect these neutrinos, at a rate very close to the predicted rate. The rate is off by a factor of about 1/3, but when you consider that the value for neutrino emission could be ANYTHING (?!) the fact that we get it within better than one order of magnitude is rather promising.
3. In addition, if you assume hydrostatic equilibrium within the sun or some other star (pretty reasonable considering that we've seen many stars for thousands of years with little or no change in their appearance), you can calculate the pressure and temperature at the center. You get something on the order of 10-100 MK temperature, at about the turn-on range for nuclear fusion, with correspondingly high pressures.
1 and 2 both indicate the existence of some nuclear-based process fueling stars. Some precise details might be off, but the general idea is right. #3 is coincidental.
Details of the solar spectrum have nothing to do with what goes on in the core - the core emits primarily gamma radiation, along with particle kinetic energy and neutrinos. The photons are thermalized as they travel up through the Sun, so they tell little or nothing about activity in the core. neutrinos, on the other hand, pretty much pass through unscathed, so we get a direct image of activity in the core.
Reply
See my message to L.P. above.
Also, there is always the possibility that the heavier elements are only produced in the center of galaxies, which might well explain the different populations of stars.
Jeremy Carlo (2)
In the center of galaxies?
Not sure that would explain properly the distribution of Pop I and Pop II stars.
Besides, we do know from high-energy experiments that many of the laws of physics as known do seem to apply at very high temperatures and very high energy levels - the theory of the sun's core is based upon that (atomic bomb experiments, particle accelerator experiments, etc.)
Reply (2)
You should probably also mention the 40 or so years of fruitless attempts to make controlled nuclear fusion work. After all, this (and not some explosive device) is supposed to be a small scale model of the sun. It is inconceivable that this failure is just due to technical problems but it clearly indicates flaws in the underlying theory.
Of course, without a proper knowledge of the physical processes at work it makes little sense to speculate about details of the galaxy- formation and -evolution.
Jeremy Carlo (3)
We can get fusion to work just fine.
It is done with hydrogen bombs.
Limited amounts of fusion have been observed in particle accelerators.
Large amounts of fusion have been caused in tokamaks.
The problem is trying to get more energy out of the system than we put in. It's all a question of proper plasma confinement, raising the gases to high enough temperatures and maintaining those temperatures without excessive loss through the walls of the tokamak, maintaining a magnetic field to confine the plasmas (quite difficult).
The problems with fusion (controlled fusion) are entirely of ENGINEERING, not SCIENCE.
Comment by Dave Barlow
You obviously think that controlled nuclear fusion is an easy process to reproduce or engineer. If I may ask, why?
The temperatures and pressures involved for sustained fusion are truly, well, astronomical. It only happens in Stars. I strongly doubt we have the engineering skills to reproduce the conditions at the centre of a small M class star, at least not yet. The JET experiment is none the less a good experiment to attempt as it helps understand what is required to make a proper fusion power station, albeit on a smaller scale than a stellar core. Fusion was achieved by focussing 3 die lasers at a point some years ago but as Jeremy Carlo points out, the problem is getting more energy out than put in.
If you are more knowledgeable about the engineering requirements to make a fusion reactor I am sure the guys at JET would dearly love to hear from you. After all, the best way to make a name is science is to prove everyone else wrong.
'Of course, without a proper knowledge of the physical processes at work it makes little sense to speculate about details of the galaxy- formation and -evolution.'
Sorry, I missed something obvious here. What has Galactic Evolution got to do with Fusion processes in Stars? One is to do with atomic behaviour the other to do with many interacting physical processes.
I'll freely admit that galaxy evolution is very much in it's infancy as a theory. But that is the nature of science, start with something we don't understand then gain understanding by carefully making mistake after mistake until some sense is made of the world. Saying that, more is understood of Galaxy evolution than you might realise. Look up Lin-Shu density waves, DeVaucoleurs Law and Stochastic Models of spiral galaxies. Ellipticals are poorly understood.
Last I heard very little was understood of the processes in Thunder Clouds and long term climatic change. Not understanding one detail of a larger model doesn't invalidate a weather forecast of thunder tomorrow.
Reply
It seems strange that governments would go ahead with a project costing billions without being certain about the exact engineering requirements, and it would be a farce to target this for a period of 40 years or more during which the rest of technology can be expected to overtake itself twice.
The occasional 'success'- stories may have helped to secure more government funding, but have apparently contributed little to the understanding of how to make sustained fusion work.
This all points very much to the possibility that one or more of the original theoretical assumptions are very badly wrong and it remains to be seen if we can ever construct the necessary technology on the basis of a revised theory.
I mentioned galaxies because one can expect much higher temperatures in their center than in stars:
if one assumes that 1% of the initial mass of the galaxy has collapsed towards its center during its formation rather than into stars, this would yield a 'superstar' with a radius of about 5 AU and a gravitational particle energy of about 10
9 eV i.e. a temperature of 10
13 Kelvin.
If anything like this is needed to produce heavier elements, it would be no surprise that it can not be reproduced in the laboratory (as mentioned, at least the electromagnetic emission of the sun could well be explained through electronic processes in the solar atmosphere alone).
At these energies physical processes might exist that we are not even aware of today, including processes inverse to fusion which would enable one to interpret the universe in a steady- state sense.
It would also be interesting if the observations of 'supermassive black holes' in the center of galaxies can be re-interpreted in this way.
Comment Jeremy Carlo
You mention several decades of failed attempts to achieve controlled nuclear fusion.
Let me make it clear that the difficulties in achieving controlled nuclear fusion are practical, and not theoretical, in nature.
Perhaps I am misunderstanding you, and if so I apologize in advance, but you seem to be implying that there is some fundamental flaw in our theoretical understanding of nuclear fusion, and that in fact nuclear fusion does not occur.
That is a physics myth, which I think you should add to your site.
Nuclear fusion has been achieved numerous times in fusion (hydrogen) bombs. If our theoretical understanding of fusion were wrong, then all the calculations done by Teller et al. would have had no correspondence to reality, and the test at Bikini Atoll would have failed miserably.
But as we all know the bomb went off just as planned. Many others, made by several nations over several decades, have also worked as planned.
Controlled fusion can and has been achieved under laboratory circumstances; energy output, gamma spectra, neutron emission, and other standard indicators tell us that our theoretical understanding is for the most part correct.
Tests for controlled fusion have NOT failed; they have succeeded from a theoretical standpoint as they have demonstrated the correctness of our understanding of fusion. If you believe there is a problem with our theoretical understanding of nuclear fusion, Teller is still around - perhaps he would be interested in why his life's work was all in vain and that the numerous tests of his calculations have all passed entirely by sheer luck.
What we HAVE NOT been able to do is get more energy out of the reaction than we put in. As I'm sure you know, nuclear fusion requires temperatures on the order of 10
8 K in order to work. Achieving and maintaining such temperatures requires a vast deal of input energy, and even more energy is required to maintain the enormous magnetic fields required to confine the megakelvin plasma. When this enormous input energy is subtracted from the energy created by fusion, achieving break-even is extremely difficult. It has been achieved, but only for short times.
Not being a policy person, I leave the question of government funding of fusion research to someone far more qualified than myself. However, I will state that if you are using public policy decisions to determine the validity of scientific ideas, you are certain to fail.
About the center of galaxies forming all "metallic" (i.e. all elements heavier than helium, Z>2) elements, that simply does not fit with observations. Metal-rich gas clouds and Population I stars are found throughout the spiral arms of galaxies, not just at galactic centers. Remnants of stellar explosions are observed to be greatly enriched in heavy elements with respect to their environs, which indicates that fusion processes are taking place far from the center of the galaxy.
If you see red paint spilled onto the middle of the street and an opened can of red paint four feet away, do you conclude that the splotch paint came flying in from out of nowhere 500 feet away, and the presence of the opened can three feet away is a pure coincidence? Absolutely not. Why do you do that with nucleosynthesis?
Spectral signatures of heavy elements have been detected in the debris from supernova explosions, and those of moderately heavy elements (Z ~ 6-14) in planetary nebulae.
And IIRC, gamma rays from Co-56 and Co-57, two very short-lived isotopes predicted to be present in supernova explosions by conventional stellar nucleosynthesis theory were detected in the fallout from SN 1987A in the LMC. Those were detected alongside a huge burst of neutrinos (fusion, perhaps?).
Putative conditions in the centers of stars (derived by equating hydrostatic pressure and radiation pressure with inward gravitational forces) have been duplicated (or at least approached) under laboratory conditions, so it is no great exaggeration to say that we have a basic grasp of the physical processes occurring in stellar cores.
PS: You may wish to reconsider your calculations for your postulated "super-star." Neglecting the dynamical issues with such a huge entity (and there are many!), this object would collapse to a black hole!
The mass of the star is, by your definition, 1 % of the galaxy's mass; this works out to about 1 billion solar masses, about 2x10
39 kg. The Schwartzschild radius of such a massive body is 2GM/c
2 ~= 3x10
12 m ~= 20 AU. You stated a radius of 5 AU, comfortably within the Schwartzschild radius.
Reply
Let me again make it clear that I do not categorically deny the existence of the fusion process. As I have not worked in this field before, I have, like most people, only second- or third- hand information here and can therefore not make any definitive judgments.
What I know for sure is that, contrary to common opinion, energy conservation (and in fact the notion of energy in the first place) is a concept from classical Newtonian mechanics and can not be applied to radiative processes (
more). Observations of spectral lines in sufficiently dense plasmas (so that the plasma- (Stark-) broadening exceeds the natural broadening) prove clearly that their intensity can not be calculated with the Bohr-Einstein radiation formula (E=h*f; f=frequency) but is enhanced proportional to the broadening.
Applied to the sun my estimates indicate that the effect could indeed account for its radiative output and furthermore that this could be covered through gravitational energy alone for billions of years.
Nuclear fusion may nevertheless exist in stars, but I do not think that the corresponding theory is so well established that it would not be worth speculating about different scenarios in the light of the above mentioned evidence.
Regards the gravitational collapse of stars:
it is a general misconception that stars would collapse under their own gravity without an opposing force like radiation pressure. Any gas cloud contracts only to the point where it has gained enough kinetic energy so that the equilibrium condition E
kin=-E
pot/2 (virial theorem) is satisfied. In other words, any gaseous mass can support itself through its own hydrostatic pressure gradient provided it does not lose any energy, i.e. a fusion core is certainly not necessary for stability (in any case, as explained under
Radiation Pressure on the main page, radiation would not provide any pressure effect).
Any further contraction can only occur if the system loses energy due to inelastic collisions of particles. This can account for the formation of stars and probably also galaxies. However, once the density becomes higher than about 10
24 cm
-3, atoms cease to exist (only nuclei and electrons remain) and therefore also the energy loss due to inelastic collisions. This is what defines the radius of the star. The only energy loss is now due to the collisions in the less dense atmosphere (which results in the radiation of the star) but this is so small that it does not produce any noticeable changes in the size of the star over shorter time scales than billions of years.
For the massive object suggested by me the changes would be particularly slow as the cross section for energy loss processes like radiative recombination and collisional excitation are extremely small due to the high kinetic energy associated with the enormous gravitation (collision cross sections typically decrease like E
-2 - E
-3; see
https://www.plasmaphysics.org.uk/research/recrsect.htm for the radiative recombination cross section).
This also means that the object would be practically invisible despite its size, in accordance with observations of the galactic centre.
I can't see what the size of a self-gravitating body should have to do with its dynamical stability.
There is only the possibility of a gravitational instability on a smaller scale in case of spatial inhomogeneities (this can account for the formation of normal stars throughout the galaxy), but this works only below a certain temperature of the gas volume and therefore certainly not for the final stages of the collapse of a super-massive object.
A self-gravitated body of 10
9 solar masses should dynamically be just a scaled up version of a normal star and therefore be as stable.
The distribution of heavy elements within a galaxy depends obviously not only on the location of the fusion region but also on transport processes. An outgassing of material rich in heavy elements from the suggested object in the galactic centre could well lead to a corresponding contamination in other parts of the galaxy. It is obvious that this will be gravitationally confined to the galactic disk and also that it will tend to be 'swept up' by the denser regions (i.e. the spiral arms).
The fact that the chemical composition of stars looks different after an explosion is not really surprising and does not necessarily indicate the presence of fusion:
in hydrostatic equilibrium, heavier elements are concentrated closer to the centre of star due to the effect of gravity and are therefore not so abundant in normal stellar spectra which only give information about the outer layer (the atmosphere). If the latter is blown off, the apparent concentration of heavier elements will therefore obviously increase.
The neutrino burst during a supernova explosion is of course less easy to discount, but then again this is unrelated to the normal life of the star for which the neutrino flux (at least for the sun) still poses more questions than answers.
Anyway, I do not think that publicly accessible information concerning nuclear weapons should serve as a basis to make judgments about the validity of scientific theories. Because of the obvious sensitivity of the issue, I can not imagine that the information released by the military gives an accurate representation of the truth.
In fact, the only open display of nuclear power so far (at Hiroshima and Nagasaki) could well be considered as a failure of science, as it caused, to my knowledge, much more destruction than theoretically predicted, probably again an indication that plasma and radiation physics are responsible at least for some of the effects ascribed to nuclear physics.
Comment by Dave Barlow
I think it's a case of funding blue sky research which may cure our energy requirements easily. Or may not. Government as well as private corporations have often spent large wodges of cash on projects that are speculative. Without trying you never know if it would have worked. A lot is learned in the process either way.
As I have no say with who allocates budget in Whitehall I can only speculate on reasons.
I honestly don't think the failure to get sustained fusion to work indicates a fault in the theory. As I said, the conditions under which fusion occurs is extreme, keeping it controlled is a complex engineering problem.
The real problem that faces the theory of fusion is the solar neutrino problem. One solution I have heard to this is that neutrinos change flavours at will. Frankly I find that far fetched but not impossible. The problem is there is no evidence to back the theory so this remains a problem.
Existing stellar models based on fusion processes are highly effective at predicting the types of stars observed, their bulk properties and observed ratios of elements. From that view fusion theory looks good.
Regards the 'super-star' in the galactic centre:
As far as I know there is no evidence for this. The evidence for galactic centre masses in the range of 10
6-10
9 solar masses is very strong, based on velocity of other stars and gas clouds in galactic centres. This mass is non-luminous though. Recent images from Hubble show the conditions of our galactic centre very nicely, no large luminous object is seen there.
Assuming 1% of a galaxies mass was a single star in the centre. This would yield a central star of mass about 10
6 solar masses in our galaxy. Such a monster would be massively luminous, highly unstable and out gassing huge amounts of material, basically a larger version of S Doradus and it's ilk. It would also have a very short lifetime, in the million years range. It would very rapidly form a black hole. Existing models basically say no star this large could form, S-Doradus appears to be at the upper most limit for mass for stars to form. Something akin to this, big central stars, may have occurred during the pre-quasar era when galaxies where forming but million solar mass stars do not exist now.
Heavier elements are created during supernovae explosions with the rapid fusion process and is backed up by observation. Early stellar populations are metal poor (metal being anything heavier than Helium) with later populations being metal rich.
Not sure what you mean by electronic processes in the Sun. The Suns atmosphere is, as you probably know, one very complicated plasma with magnetic field lines running though it. Models of the atmosphere are on a par with models of the earths atmosphere.
Don't forget that CERN and other colliders are investigating energies in the GeV ranges. Last I heard CERN had detected faint traces of the elusive Higgs. Nothing unusual (contrary to known physics) has been detected yet.
How do you mean, inverse to fusion? Fission/radioactive decay is effectively the inverse process. Iron being the end result of fusion in stars and radioactive decay in heavier elements. Hence the iron rich core of Earth.
I can not see how you can interpret the Universe in a steady-state sense using any model. All evidence is that it is dynamic and expanding. The high-z supernova team indicate the expansion to be increasing. Personally I think that needs verification still but it is interesting. COBE and BOOMERANG both detected the CMB, something no steady state model has ever successfully predicted.
Reply
I am certainly in general not opposed to speculative technological projects if these can somehow be justified (and the need for new energy sources within the next few decades is obvious). However, one should also be prepared to reconsider the fundamental scientific assumptions if things do not work out as anticipated (for a complex project like controlled nuclear fusion, science becomes virtually inseparable from engineering and it would be rather shortsighted to squarely blame only the latter in case of unforeseen problems).
In astrophysics, existing stellar models may be effective in reproducing the bulk of observational data, however this does not necessarily prove they are correct. The Ptolemaic (geocentric) system of the universe also succeeded in predicting the movement of the planets quite accurately (and if it didn't a few more epicycles were simply added on), but it was clearly unacceptable as a physical concept.
At least with regard to the light emitted from the stars, fusion does in fact not seem to be necessary at all, as results from my own work indicate (I have outlined this before and again in my
reply to Jeremy Carlo above which also addresses your points concerning the physics of the suggested 'super-star' in the galactic centre and the possible connections to the stellar populations in the galaxy).
Energies similar to or even higher than those associated with a supermassive object of the suggested size (which should be 10
9 and not 10
6 solar masses as you state) may have been achieved in collidors, but I presume that the particle densities in the latter are simply too low to enable complete reaction cycles (of whatever processes occur) to take place.
A hypothetical reaction inverse to fusion would simply tend to re-create hydrogen from the heavier elements. I can't think of any physical process that has not got its inverse of some kind, so it would be quite strange to assume that fusion has none.
This would also invalidate the argument of cosmologists that the present chemical composition of the universe is not compatible with an infinite life time as nuclear fusion alone would irreversibly turn hydrogen into heavier elements. An additional inverse process would establish an equilibrium of loss and production for each element and therefore a constant chemical composition over longer (and indeed infinite) periods.
The concept of an expanding universe is simply inconsistent (I have discussed this and other cosmological problems with Todd Kelso in my
Cosmology Forum). This of course means that one even has to demand the above mentioned 'inverse fusion' process.
Comment by George Pappas
The problem with the controlled nuclear fusion today is that we can't maintain the fusion for long periods of time. The reason for that is the complexity of system. A plasma confined by a magnetic field is a magneto hydrodynamic(MHD) system. In this system there are created several types of waves called MHD waves. These waves are the problem and not that we don't understand fusion. Under some conditions these waves are amplified causing the plasma to divert from its course and hit the walls, resulting to the cooling of the plasma and the distraction of the machine. So the problem is technical. We must find a way to control these waves.
In a previous post you mentioned something about the center of galaxy's and the creation of the heavy metals there. Lets forget for a moment that this condition wouldn't be stable. How would these metals get out of there?
Reply
You are correct to assume that plasma physics presents a problem for the heating in controlled fusion , although this should actually be due to (stationary) non-linear plasma - oscillations which limit the possible organized energy input to a magnetized plasma (see my web-page
https://www.plasmaphysics.org.uk/research/plasrese.htm). Also, the usually assumed 'pinch- effect' (which is supposed to increase the particle density) will be largely prevented by electrostatic plasma polarization fields which tend to offset the vxB Lorentz- force (as well as any applied electric field perpendicular to B (see under
ExB Drift on the main page).
These aspects should however be in any case irrelevant for the production of radiation through fusion in the sun, which can be questioned on the basis of other evidence (mainly the circumstance that the usually assumed form for calculating radiative intensities leads to an under-estimation for sufficiently high plasma densities, i.e. the radiative output of the sun could well be accounted for by electronic processes in the photosphere alone, as explained in my earlier postings (see my
reply to L.P.'s comment above) ).
With regard to the stability problem and the proposed production of heavy elements in the galactic center see my
reply to Jeremy Carlo's comment above .
Comment by Mark Gallaway
I'm not sure how you can claim that fusion does not occur in the sun, when your there is not any really strong observation evidence that your alternative method is on going. Supply me with an observational difference between your process and nuclear fusion and I'll go and test it for you. However, before I do I'd like to point out.
1 The neutrino detection rate is correct for fusion.
2. The stellar evolution models and observation fit - which they wouldn't without fusion.
3. We see carbon oxygen trawl up in AGB stars
4 How would you get metals from the centre of the galaxy and into the sun?
5 Older stars like M dwarves have lower metallically and aren't making carbon and oxygen.
I could go on for quite a while. However, as I said at the beginning - Prove your theory, it's nothing if you can't prove it.
Reply
First of all, as I mentioned already somewhere above, I do not categorically exclude that nuclear fusion occurs in the sun, but I only claim that it is insignificant for the radiation output of the sun, because a) the radiation can be fully explained in terms of electronic processes in the sun's atmosphere (see the entries above and also my page regarding
Coronal Heating on my site plasmaphysics.org.uk) and b) the energy of particles in the sun is much too small to produce a significant amnount of nuclear fusion (this is unless one involves flawed concepts like the quamtum mechanical
tunnel effect here). Much more massive objects than stars are needed to provide the required kinetic energy of particles, and supermassive objects in galactic centers are the only realistic candidates here.
The observed neutrino detection rate was until rather recently in fact considerably lower than predicted by stellar and nuclear theory. It was only after the Standard Model of particle physics was teaked such as to allow a 'flavour' change of neutrinos that it was consistent with theory. Likewise, stellar evolution models are also tweaked such as to be consistent with observations. As implied elsewhere on this site (and also under the above link regarding coronal heating), stellar models rest on a number of flawed assumptions regarding the physics involved (for instance, it is assumed that radiation is required for the star not to collapse on itself, when indeed no radiation at all is required in hydrostatic equilibrium due the presure gradient)).
And when I am suggesting that heavier elements are largely produced in a supermassive object in the galactic center rather than in stars, then this is consistent with observations as the metallicity of stars decreases with distance from the galactic center (the heavier elements are merely diffusing outwards and occur therefore diluted further out).
Lastly, I am not really introducing any new physics here, but I am just tying up some loose ends on the basis of fundamental physical principles whilst avoiding the flawed assumptions in present mainstream theories.
As I said alerady, the present theory of the sun is theoretically flawed and only made apparently consistent with observations by tweaking it accordingly, in a similar way as for instance the Ptolemaic (geocentric) system of the universe was permanently tweaked to match the observations. The alternative Copernican (heliocentric) system could at first also not be confirmed for certain by observations (in fact the geocentric was more accurate before Kepler developed the concept of elliptical orbits) but eventually everything fell into place with it. Of course, the situaton is much more complex here as a lot of different physical theories are involved (each of which may not be correct), but I am confident the same will eventually happen here as well.
Comment by Nikolai Bouianov
Nuclear fusion reaction was never done in the labs. The main problem here is neutrons. What scientists did, they combined some light elements, which already contains neutrons like Deuterium and Tritium into heavier element. The hypothetical reaction in the Sun is proton-proton reaction, where two hydrogen atom without any neutrons produced Helium with neutrons.
Additional comment on nuclear weapon as a proof for fusion reaction:
Thermonuclear reaction required tremendous pressure and temperature to take place. Such condition created by fission reaction, i.e. we have bomb in the bomb. Thermonuclear content of such device is around 10%-15%. The methods of bomb power measurements have approximately the same precision. How do we know that thermonuclear reaction works?
Reply
Well, neutrons would be a problem if they could produce enough. Fact is, so far no sustained nuclear (and no net gain of energy) has been achieved yet, despite 60 years of research and experiments. The point is that the underlying theories are incorrect in many ways, be it the
plasma physics or
quantum/nuclear physics. It is often claimed the problems with fusion would be of a technical nature, but you don't start a project of this size and cost if you are not sure about the technical challenges and how to meet them. Problems only occur if it turns out you misjudged things, and this can only be due to theoretical misunderstandings of the physics involved.
It is just so (in my opinion anyway) that the sun is not powered by nuclear fusion. Its radiation can be fully explained in terms of electronic processes in its atmosphere (see my page regarding
Coronal Heating in this respect). Radiation from the sun's centre could not penetrate to the surface anyway, due to the very dense plasma it has to traverse (which would 'scramble' any sinusoidal electromagnetic wave to a random (i.e. undetectable) signal). There may be some nuclear fusion at the centre, but this is only going to change the composition of the material (i.e. producing heavier elements), nothing more. The radiation is solely produced at the surface of the sun.
I don't think that nuclear weapons can provide any useful guide and information here: first of all, making something go 'bang' in a rather limited number of tests can not provide very good insight into the underlying physics; secondly, I do not think that the military are trustworthy scientific sources; giving open and transparent information is just contrary to their nature.