
#55
Sep109, 08:06 AM

Astronomy
Sci Advisor
PF Gold
P: 22,792

That is 10^15 eV and if one were to convert that to temperature in the usual way one would say 10^19 kelvin. Ten billion billion kelvin. But are there processes currently going on in our galaxy that you would characterize as having a temperature of ten billion billion kelvin? I guess my point is that temperature can be a tricky concept because the particles are produced by nonequilibrium processes. We have this mental reflex to convert particle energies to temperature, but it does not always give the right intuitive understanding. Cosmic ray particles with energies in excess of 10^20 eV have been observed. If one converts that in a kneejerk way to temperature, one would say 10^24 kelvin. This is more than a "few billion degrees". It is a quadrillion billion degrees. But does that conversion to temperature really help you understand cosmic ray particles, or the processes that produce them? 



#56
Sep109, 08:16 AM

P: 2,456

Yes, but there is no clear explanation for such rays.
So yes, they have been observed. For example, in supernova explosion temperature is only 10**11  10**12 K 



#57
Sep109, 09:38 AM

Astronomy
Sci Advisor
PF Gold
P: 22,792

I'm not sure you understand my point. I am questioning the usefulness of assigning a temperature to a supernova and then expecting that temperature to characterize the energies of the cosmic rays accelerated by some nonequilibrium supernova processes. For example see this paper published in Nature.
http://arXiv.org/abs/astroph/0411533 Highenergy particle acceleration in the shell of a supernova remnant H.E.S.S. Collaboration: F. Aharonian, et al 9 pages, 3 figures, published in Nature (Submitted on 18 Nov 2004) "A significant fraction of the energy density of the interstellar medium is in the form of highenergy charged particles (cosmic rays). The origin of these particles remains uncertain. Although it is generally accepted that the only sources capable of supplying the energy required to accelerate the bulk of Galactic cosmic rays are supernova explosions, and even though the mechanism of particle acceleration in expanding supernova remnant (SNR) shocks is thought to be well understood theoretically, unequivocal evidence for the production of highenergy particles in supernova shells has proven remarkably hard to find. Here we report on observations of the SNR RX J1713.73946 (G347.30.5), which was discovered by ROSAT in the Xray spectrum and later claimed as a source of highenergy gammarays of TeV energies (1 TeV=10^{12} eV). We present a TeV gammaray image of the SNR: the spatially resolved remnant has a shell morphology similar to that seen in Xrays, which demonstrates that veryhighenergy particles are accelerated there. The energy spectrum indicates efficient acceleration of charged particles to energies beyond 100 TeV, consistent with current ideas of particle acceleration in young SNR shocks." If you make a simpleminded conversion of "beyond 100 TeV" to temperature, then it does not make sense. The simpleminded conversion of 10^14 eV would be 10^18 kelvin. That is one billion billion kelvin. No one supposes that the supernova explosion is characterized by a temperature of 10^18 kelvin. In fact it is an intricate process, or combination of processes, some of which do not have a welldefined temperature. One would not say that the supernova has a temperature of "beyond 10^18 kelvin", and yet it apparently produces cosmic ray particles accelerated beyond 10^14 eV. Something more recent on this general topic (supernova remnants and cosmic rays) is a 2008 white paper: http://arxiv.org/abs/0810.0673 



#58
Sep109, 11:03 AM

P: 2,456

marcus, ah, I see, I agree.
BTW, any news about how such particles violate GZKlimit? 



#59
Sep109, 11:30 AM

Astronomy
Sci Advisor
PF Gold
P: 22,792

As I recall, they suspect that cosmic rays are either generated in our own galaxy or come from comparatively nearby active galactic nuclei (AGN). Yes, I checkedWikipedia gives some numbers. The GZK cutoff is 5 x 10^19 eV, and it only applies to distant sourcesthe mean free path for the reaction with the CMB is 160 million light years. 160 million lightyears is fairly close to us. There are enough AGNs within that range. If I remember there used to be a puzzle about GZK, somebody had seen too many UHECR, they thought. Then the Auger observatory found there were not too many. The UHECR could be explained as coming from nearby AGN. So this puzzle was cleared up. I think Auger even pinpointed some nearby AGN sources of cosmic rays (though not of this ultra high energy.) 



#60
Sep109, 12:51 PM

P: 343





#61
Sep109, 01:28 PM

Mentor
P: 15,568





#62
Sep109, 01:53 PM

Astronomy
Sci Advisor
PF Gold
P: 22,792





#63
Sep109, 02:31 PM

Sci Advisor
P: 5,306

You should take into consideration that for many known mathematical frameworks you can construct a metaframework from which the individual frameworks can be derived. In that case the metaframework can provide a selection rule. 



#64
Sep109, 02:42 PM

P: 2,456

Could you explain your motivation, why do you want to find some "selection rule"?
Selection rule adds complexity. Number 456 contains more information then ALL integers, because you can ask "why 456? what is selection rule?" For ALL integers you dont need a selection rule. 



#65
Sep109, 10:49 PM

Mentor
P: 15,568

The most positive interpretation comes from Auger themselves: see their presentation at ICRC 2009 in Lodz. They say that the correlations have "not strengthened" or "weakened", despite having added more data to the analysis. Others did the natural thing and subtracted the new numbers from the old numbers to look at the correlation in just the events they added. Nothing much there. 



#66
Sep109, 10:54 PM

Astronomy
Sci Advisor
PF Gold
P: 22,792

Glad to get new information about an interesting question like the origin of UHECR.
The most recent thing I've seen about this is April 2009 http://arxiv.org/abs/0904.4277 Correlations between Ultrahigh Energy Cosmic Rays and AGNs Glennys R. Farrar, Ingyin Zaw, Andreas A. Berlind (Submitted on 27 Apr 2009) "We investigate several aspects of the correlations reported by the Pierre Auger Observatory between the highest energy cosmic rays (UHECRs) and galaxies in the VeronCetty Veron (VCV) catalog of AGNs. First, we quantify the extent of the inhomogeneity and impurity of the VCV catalog. Second, we determine how the correlation between the highest energy Auger UHECRs and VCV galaxies is modified when only opticallyidentified AGNs are used. Finally, we measure the correlation between the published Auger UHECRs and the distribution of matter. Our most important finding is that the correlation between UHECRs and AGNs is too strong to be explained purely by AGNs tracing the large scale distribution of matter, indicating that (barring the correlation being a statistical fluke) some substantial fraction of UHECRs are produced by AGNs. We also find that once we take into account the heavy oversampling of the VCV catalog in the Virgo region, the lack of UHECR events from that region is not incompatible with UHECR having AGN sources." If you have a link handy to some particular abstract from the conference you were talking about, I'd be glad to give a look. 



#67
Sep209, 07:22 AM

P: 11

Maybe it's time to redefine temperature.




#68
Sep209, 03:17 PM

Sci Advisor
P: 5,306

I believe that we are living on one of many possible worlds. Possible means logically or mathematically possible = (at least) consistent. As I said I think that a universe with (e.g.) a fourth heavy fermion generation would be "possible" and would not differ so much from ours. So we must take this into account when we study candidates for a ToE. Then I believe that (even if you insist on some kind of a multiverse) not ALL but only a certain SUBSET of all possible worlds exist "somewhere". Of course I do not know what this subset is but I strongly believe in this subset. Reason 1: I don't like the multiverse idea, because it has too much metaphysical ballast and does not satisfy Ockham's razor criterion; I don't believe in an entity that is in principle invisible, not measurable and therefore unphysical. Compared to the multiverse one selection rule seems to be much simpler and much easier to believe in (at least for me). Reason 2: All discussions regarding the multiverse idea (manyworlds interpretation, landscape) I ever participated in came sooner or later to a point which I would describe like "I cannot explain why it's this way or that way  and therefore it's both ways!" That's not a sientific argument but an excuse only. Reason 3  and this is the most important one: even if you insist on the multiverse idea, it is by no means clear why ALL logically consistent ToEs should be physically real  why not only a certain subset? Compare it to evolution: not ALL possible species are alive, but only a certain subset. Why is this? Simply because there are selection rules (not hand made, but external to the species' ToE framework = the DNA, namely the environment) which suppress or constrain the evolution. In our case this could be some metatheory, but nevertheless it must not be excluded. So this selection rule could restrict the number of real worlds to just ONE, or it could drive an evolution of universes such that we are living in a TYPICAL one. (Smolin's idea was that a universe spawns children from black holes, so a selection rule is that a typical universe is one in which the numer or density of black holes is maximized such that as many baby universes as possible are spawned  I don't think he was able to define this mathematically and prove why our universe nearly maximizes the number of black holes). Finally I would like to explain reason 4  even if I did not study the paper in question in all details: From a philosophical point of view I still do not see how the concept of a DESCRIPTION of a world is converted into the WORLD itself. I still believe in a kind of dualism, namely that the world and its description are two different "entities". Therefore the mathematical frameworks do not exist on the same level as the worlds. Of course there is a sketch of a proof: The mathematical framework is eternal and exists "forever". It does neither exist "in time" nor "in space". But a universe can be created out of "something" and eventually it can fade away. Therefore the lifetime of a universe could be finite, whereas the lifetime of the corresponding mathematical framework is certainly not (homework: when will the prime numbers die?) If you believe that the prime numbers will never die, then a) either the universe (by similar reasons: all universes!) is (are) eternal, which means that only eternal universes are allowed, which is a selection rule! b) or the prime numbers exist in some "outer space" = some metatheory in which the "universes" = ToEs are embedded. In that case the eternal framework turns again into an eternal description of a mortal world, which proves that the two entities in question do not exist on the same level. (Logical positivists grounded some of their disproofs in a mismatch of categories. E.g. they claimed that the color red is not identical with a certain wavelength, but is its representation. I have the feeling that this concept for a ToE is vulnerable due to similar reasons). My conclusion is that I am still not convinced that the entity "description of the world" is identical with the "world" it describes. Last but not least I would like add an idea how ToEs could be categorized:  first requirement is that the ToE incorporates all known interactions in some way, e.g. as lowenergy effective theories  second requirement is that the ToE is a consistent mathematical framework, i.e. it must be mathematically welldefined  third requirement is that the theory must postdict at least some known facts like the standard model gauge symmetries, number of generations, number of spacetime dimensions etc.  forth requirement is that the theory must predict new phenomena which should be (at least in principle) falsifiable by experiment A (meta) requirement) for a (meta) ToE is that the theory in question can at least support why she is the ToE. That means if the ToE contains a certain mathematical structure, there should be an explanation in terms of deeper structures or insights why this structure MUST be contained. This is subtle, of course. EXample: if the ToE is grounded on local gauge symmetries, I would like to know WHY. 



#69
Sep309, 01:37 AM

P: 11

Maybe you can use Knot theory to satisfy Ockham's razor criterion in the multiverse idea.




#70
Sep309, 02:13 AM

P: 2,456

Tom,
Regarding 1,2,3 and Occams razor. In informational sense, “information should not be multiplied unnecessarily”. When we build something, we add building blocks, adding new information an every step. That is why every new stone you put in the building must be well justified. However, using this method you can add only finite number of stones/entities. You can’t define integers by providing a complete list, right? When we manipulate with infinite numbers of entities we go in the opposite direction: we start from the Universum, and then remove something. Each removal adds new information (and list {12438, 59859599, 858585, 77} contains MORE information than a list of ALL integers), so each removal must be justified. It seems you understand it and for that reason you call a “selection” rule (selection – taking one from many = removing others). Again, you are not asking how to justify the creation of OUR universe( that would be natural for one going from nothing to the Universum), you seek the justification of removal for the others. So we are on the same page. But: if we go in the opposite direction, from the Universum, then any REMOVAL adds new information and hence is a subject of Occams razor. Going from nothing to the Universum we must justify any addition, going back we must justify any removal. You mentioned Occams razor and on the very next step started inventing NEW entity which you call a “selection rule”. Do you agree with my logic? So Occams razor is the very reason I believe other Universes exist. You know, there are some naïve questions like “what is space?”. People tend to ask such questions because of the intuitive conception that if something is not made of something then it is void and collapses. So the most satisfactory answer would be “space is made of spacions”. “Ah, yes, it makes sense”. Of course, after a while they would start wondering what spacions are made of. We always had a situation that something was made of something: molecules of atoms, atoms of elementary particles, then came quarks, now we expect them to be made of strings. We so got used to it that we are not psychologically ready to the fact that in TOE that infinite reduction MUST END. Say, you are looking at the page with few beautiful equations. These TOE equations describe, say, some function Q in some quaternionvalued space and some equations that function Q obeys. All other entities: time, space, gravity, particles, emerge from these equations. But you start to worry. this is just an equation What makes it real, you ask yourself. You are desperately trying to find a magic wand which would touch the paper with formulas and the formulas will start to “live”. You are not satisfied with the fact that this IS TOE. If I would say that the reality is made of “realityons”, obeying these formulas, you will be satisfied, right? If I would say that there are JUST formulas, you will be not. You will be even satisfied if I would say that these formulas are emulated on some supercomputer. Because again it shows that there is smoothing behind the curtain – realityons, computers, or something. Max Tegmark article is so shocking because he insists that there is nothing behind the curtain – no spoons, no realityons, no supercomputers. Fundamental notions are fundamental only if they do not consist of anything. Fundamental notions do not need any agents to be “incarnated”. Otherwise they are not fundamental and the theory is not a TOE. You are mixing 2 things: (A)“eternal” as “lasting for eternity of time” = “being infinite in time” (B) “eternal” as “existing independently of time” = “something to which a concept of time is not applicable” In your quote I put marks (A) and (B) showing how you mix these notions. In the highlighted part you compare (A) and (B) which is incorrect. 



#71
Sep309, 09:27 AM

P: 640





#72
Sep309, 04:12 PM

Sci Advisor
P: 5,306

First of all I don't think that you responded to reason 2 and 3. Regarding Ockham's razor and reason 1 we should not waste too much time.
Some clarifications and remarks: My basic intention is INDEED to mix these two "categories of existence", simple because the theory you are describing FORCES me to do this. I start with my statement that each mathematical framework is eternal; there seems to be no metamathematics which "creates" or "kills" mathematics. So as mathematics has not been "created" at some "time", all mathematical frameworks are eternal, too. The mathematical frameworks in question do not exist "in physical time" because time (and space) are entities "emerging" from these framework (not necessarily from all frameworks, as the ToE may allow for universes where physical time does not exist. Up to now I do not mix these to "categories of existence". No my reasoning is as follows: If some specific mathematical framework DESCRIBES a universe, the existence of the framework and the existence of the universe are two different "categories of existence"; therefore their "lifetimes" are independent. Whereas the description of the universe exists "before" the universe is "created" and after it "dies", the universe itself has a finite (physical) lifetime. If a universe with finite "physical existence" IS IDENTICAL WITH the corresponding mathematical framework, you are in trouble. Either you have to forbid by some selection rule universes=frameworks with finite lifetime, or you have to lift the framework to some metalevel where its existence and "lifetimes" is again independent. You are telling me that the universe and the framework are identical. So there must be a onetoone correspondence of all entities, structures and aspects including EXISTENCE; especially you have to specify, what it means on the level of the framework that "the univeses dies" = "its existence comes to an end" = "the mathematical framework dies". Either the existence of the framework comes to an end, too, then you have to explain what that means in pure mathematics, or the theory rules out universes with finite lifetime, or the framework does not die, but then its not identical to the universe in all aspects which contradicts your theory. You have to explain how these sentences correspond to each other and how they can be formulated in a mathematically welldefined way. Assume you are right and we are living in a universe=framework created by a big bang from nothing. What was the mode of existence of the framework before the big bang and how has it been created? 


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