Talk:Greisen–Zatsepin–Kuzmin limit

Reversion
I've changed the phrasing of most of the text back to the version from May 9th. Mainly this was because it didn't appear to add much new information, while making the text longer and much less readable.

I've kept the notes about pion production, and will be happy to tweak the text to include additional points that any of you feel are currently glossed over in the text. However, the only other point that was added (about non-big-bang origin of the CMB) doesn't appear to actually change the situation (regardless of where the CMB came from, it should interact with high-energy cosmic rays). --Christopher Thomas 21:09, 20 Jun 2005 (UTC)

I don't understand
The paradox seems to hinge on the assumption that these very-high cosmic rays are extra-galactic in origin. Curiously the article doesn't claim this though it does say that they are 'from distant sources'. In any case is the number of observed events and their resolution good enough to suggest an extragalactic origin with high confidence? Also couldn't SNRs provide a source of these cosmic rays in the Milky Way? They certainly are one source of very-high energey gamma-rays. I'm probably missing something here and it would be great if someone could answer these points (at least the ones which aren't too obvious) in the article. --80.98.226.20 01:37, 3 January 2006 (UTC)


 * My understanding is that the high-energy cosmic rays are believed to be of extragalactic origin because no obvious nearby source could be found in the directions of the bursts. However, current cosmic ray observatories have a hard time detecting enough events and pinning down their directions with enough accuracy to make an ironclad case for this, so experiments are still ongoing. Even if they're of extragalactic origin, we should be able to locate the galaxies or other features that produce them. --Christopher Thomas 05:22, 3 January 2006 (UTC)


 * As far as I understand it, it is even so that we do not expect any source in our galaxy which produces particles at these energies, despite the directional resolution. --yanneman 11:09, 31 January 2007 (UTC)


 * UHECRs above the GZK cutoff could arise from either nearby or distant sources. In some theories, UHECRs could be produced nearby by the decay of hypothetical particles. At this time there are no confirmed UHECR sources. The paths of extragalactic charged particles at all but the highest energies would be bent too much by galactic and intergalactic magnetic fields to directly observe their precise origin. At the 2007 ICRC conference the Auger experiment released a spectrum confirming the observation of "a" cutoff as originally observed by the HiRes experiment. Some doubt is still expressed as to whether this steepening in the energy spectrum is caused by the GZK effect. One would expect a GZK cutoff for UHECRs of extragalactic origin. A steepening consistent with the GZK cutoff has now been observed.

Pönkle-Zedkov curves
I can't find any reference to these in the Greisen or Zatsepin and Kuzmin papers, (or anywhere else on the web), so I've removed the mention. Let me know if I'm in error. Akriasas (talk) 17:49, 13 April 2008 (UTC)

Does a variable speed of light have any bearing?
I recall reading that some scientists believe the speed of light is not constant but was in fact greater at some point in the past. This supposedly invalidates the GZK limit (or at least, the current limit) and accounts for the incredibly high energies detected. Whether this was a valid point or someone's wild speculation I don't remember, and I don't know enough about the physics to comment. Is there anything to this? Should it be discussed on the page or is it a load of bunk? —Preceding unsigned comment added by 69.36.57.3 (talk) 11:39, 13 August 2008 (UTC)

Please Consider Revising this Article
With results from the Pierre Auger Observatory confirming those presented by the HiRes Experiment at the University of Utah. See Results from the HiRes Experiment There is more than enough evidence that disproves the existence of particles above the GZK cut-off. I would recommend reading arxiv pages on HiRes results if you need more proof. --User:Brad Dober 13:26, 16 Oct 2008 (CST)


 * Can you explain? Your statement is less than obvious. Even the 2005 article you reference states "Higher statistics needed to extend analysis up to the GZK Threshold!". Jeff Carr (talk) 07:11, 24 November 2009 (UTC)

UHECR Arrival Directions Relevant?
While measuring UHECR arrival directions and confirmation of the GZK cutoff are goals of the Pierre Auger Observatory, the former has no business being in the article on the latter. Is there any reason why this was included that I don't understand? Furthermore, if it says the language is misleading. The cited Science article makes no claim that UHECR "come from" active galactic nuclei--the result is only a correlation, so a good colloquial way to say it might be that "AGN could be tracers for the arrival directions of UHECR." APfergus (talk) 18:01, 5 February 2010 (UTC)

Computation of the GZK-limit
Shouldn´t it say, in the reaction, Pi^0 and Pi^+ instead of Pi^h and Pi^h?. —Preceding unsigned comment added by 190.188.3.11 (talk) 17:00, 5 June 2010 (UTC)

The famous GZK paradox has been completely solved
Mechanism-Revealed Physics (33/40)

Completely solving the long-standing GZK paradox by discovering the mysterious source of ultrahigh-energy cosmic rays. The long-standing famous GZK paradox, one of the fundamental puzzles in physics or astrophysics, has been perplexing scientists for about four decades. The GZK paradox has been completely solved by identifying the mysterious source of ultrahigh-energy cosmic rays (P. 578 ~ 580, 5.10, Ch.5C, reference #1). Be clarified, in solving the GZK paradox, the concept and implication of black holes is based on MRBHT (= Mechanism-Revealed Black Hole Theory, P. 541 ~ 548, 5.5, Ch.5B, reference #1), rather than from current postulate-based black hole theory, i.e., mechanism-revealed black holes rather than postulate-based black holes. What is GZK paradox? GZK limit is a theoretical upper limit on the energy of cosmic rays from distance. This limit was computed by Greisen, Zatsepin and Kuzmin in 1966, based on the interactions between the cosmic ray and the cosmic microwave background (CMB) radiation. They predicted that cosmic rays with energies over the threshold energy of 5 x 1019 eV would interact with CMB photons to produce pions. Therefore, extragalactic cosmic rays with energies greater than this threshold energy should never be observed on Earth. Nevertheless, a number of observations appear to show cosmic rays from distant (i.e., extragalactic) sources with energies above this limit. The observed existence of these particles has been widely referred to as GZK paradox or cosmic ray paradox since then (ref., the encyclopedia of physics). The conclusion that the black holes in the Milky Way galaxy are the source of ultrahigh-energy cosmic rays observed nearby Earth completely solves the GZK paradox, because the crux or ‘culprit’ of the paradox was incapable of finding out the source of ultrahigh-energy cosmic rays observed nearby Earth within the previous paradigm (P. 575 ~ 576, 5.9.2, Ch.5C, reference #1; P. 578, 5.10.2, Ch.5C, reference #1). In other words, after discovering the source of ultrahigh-energy cosmic rays, the famous GZK paradox is completely (mechanistically thus essentially) solved. Therefore, in the GZK paradox, GZK limit is correct, whereas the so-called observed evidence like ‘a number of observations appear to show cosmic rays from distant galaxies with energies above this limit’ turns out to be merely the consequence of wrongly interpreting observational results within the previous paradigm. The key to understanding the solving the GZK paradox: (i) considering the solving GZK paradox together with the conclusion that black holes are the source of gamma ray bursts (GRBs), and GRBs occur via the explosions of black holes (P. 567 ~ 574, 5.8, Ch.5C, reference #1) because gamma ray is one of the four common types of cosmic rays, and together with the conclusion that black holes in the Milky Way galaxy are the source of ultrahigh-energy cosmic rays observed nearby Earth (P. 574 ~ 577, 5.9, Ch.5C, reference #1). (ii) As long as you have known the greatest equation in the history of science, which is Einstein’s famous mass-energy equation (E = mc2 or E0 = mc2), you will easily understand of the solving the GZK paradox, because the law of object’s mass doing work (OMDW) (P. 93 ~ 109, Ch.1A, reference #1), which is the root of the solving the GZK paradox (P. 895, reference #2), has also revealed the mechanism behind the greatest equation (P. 114 ~ 118, Ch.1B, reference #1). (iii) The newly established MRBHT is the key to solving the fundamentally important problem of GZK paradox.

Reference #1: 2009, Bingcheng Zhao, From Postulate-Based Modern Physics to Mechanism-Revealed Physics [Vol. 1(1/2)], ISBN: 978-1-4357-4913-9. Reference #2: 2009, Bingcheng Zhao, From Postulate-Based Modern Physics to Mechanism-Revealed Physics [Vol. 2(2/2)], ISBN: 978-1-4357-5033-3.

Ph.D., Bingcheng Zhao, The author of “From Postulate-Based Modern Physics to Mechanism-Revealed Physics” 1401 NE Merman Dr. Apt. 703, Pullman, WA 99163  USA. Email: bczhao12@gmail.com  or   bzhao34@yahoo.com   or   bingcheng.zhao@gmail.com  —Preceding unsigned comment added by 204.52.246.120 (talk) 19:14, 18 March 2010 (UTC)


 * Wikipedia is not the place to try to publish or popularize your own ideas. See WP:OR and WP:RS. --Christopher Thomas (talk) 19:18, 18 March 2010 (UTC)

Would neutrons actually be exempt from the cutoff?
I've added a "citation needed" tag to the statement that neutrons would be much less affected by the GZK cutoff. Sufficiently energetic photons (like the blue-shifted microwaves UHECRs see) should have wavelengths short enough that interactions with individual quarks become relevant (i.e. the fact that a neutron has no average charge no longer means it won't interact with photons).

That said, I'm not a particle physicist, so I don't have first hand information on the decay modes this would involve. So, a reference that works the math would be helpful. --Christopher Thomas (talk) 20:50, 16 November 2010 (UTC)
 * I don't know what the neutron cross section for interactions with high energy photons is, but it has to be something since (as you note) neutrons have internal charge distributions due to their hadronic nature, so are not immune to EM interactions. Count Iblis has just properly removed a claim that neutrons might make it past the GZK distance limit, even if they don't interact with photons. However, even that is wrong unless the neutrons have energies of 100 times the GZK cutoff. It's easy to calculate that for ultrarelativistic particles, the "gamma" time-dilation factor is about E/mc^2, which is about 5e19 eV/(9.4e8 eV) = 5.3e10 factor of time-dilation. Multiply by a neutron mean-life of 15 minutes, and for neutrons and you get a decay time of 1.5 million years, which gives an GZK-energy neutron range of 1.5 million light-years. This gets them to the nearest galaxy, or anywhere in this galaxy, but is too short by a factor of 100 to go the GZK cutoff distance, so it would need to be compensated (obviously) by having neutrons with 100 times more energy than the GZK cutoff E. A neutron that made it 30 billion light years (from vis universe edge to edge) in 15 seconds, as the removed claim went, would need an energy 1,200,000 times the GZK cutoff, or 10 MJ. This is a respectable 0.5% of the Planck energy-- about 5 sticks of dynamite. Pretty hot! S  B Harris 22:53, 7 November 2011 (UTC)

Some unclarities
They speak of "cosmic rays" all the time, but then in the section "Computation of the GZK-limit" the two reactions involve protons, is it just for protons(and charged stuff), or does it work for neutrinos too? I think it should be a little more specific? (In this paper, for instance they do plot a limit on the neutrino intensity under the name GKZ.)82.169.255.79 (talk) 21:13, 20 March 2011 (UTC)


 * The phrase "cosmic rays" usually refers only to charged particles. The paper you link to doesn't actually refer to a GZK effect for neutrinos, but the detector is claiming to be sensitive to both cosmic rays near the GZK energy threshold and to neutrino fluxes below the Waxman-Bahcall upper limit on neutrino production (something I know comparatively little about). The GZK effect was originally conceived of considering protons only since most heavier nuclei will simply be destroyed instead of losing energy when interacting with the microwave background (iron being one potential exception, but that's a whole other story). A.P. Ferguson (talk) 14:13, 21 March 2011 (UTC)


 * Thanks, ok, looks like the article of cosmic rays does say so, i guess. Perhaps this page should repeat that a little, because the term 'cosmic ray'really suggests otherwise..82.169.255.79 (talk) 13:12, 2 April 2011 (UTC)

Lee Smolin Comments
I have erased from the introduction the comments:

'''[...]where the theory of special relativity breaks down. Physicist Lee Smolin has written that if such cosmic rays which violate the GZK limit can be confirmed, and other possible explanations discounted, it "would be the most momentous discovery of the last hundred years—the first breakdown of the basic theories comprising the twentieth century's scientific revolution."'''

Lee Smolin is not a relevant scientist to comment on Cosmic rays even if he actually does it frequently. This citation uses his notability/Irrelevat arguments (http://en.wikipedia.org/wiki/Wikipedia:Notability_(science)/Irrelevant_arguments) as a way of promoting his mostly discredited ideas which are certainly unrelated to cosmic rays. Though it is true that if violating-GZK-limit cosmic rays from distant places are observed would lead to new physics, almost all the scientific community would agree that Lorentz invariance violation is an unlikely possibility. In order to expand on possible new physics a citation of scientists of the Cosmic ray community would be needed; certainly not Lee Smolin. — Preceding unsigned comment added by Matiasleoni (talk • contribs) 17:05, 30 October 2014 (UTC)

UHECR
The acronym UHECR is never introduced, I guess it means "Ultra High Energy Cosmic Ray"? But I'm not sure so I didn't change the article.