We do not understand nature, we measure it

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The Great Debate is over. In the next days you will be able to see it here. Although I had plenty of urgent things to do, I could not resist to follow the live blog by Marcel Pawlowski and Andreas K├╝pper, who kept reporting and answering questions for the whole duration of the debate. It was an interesting experience. From what I can judge, the presentation by Simon White was very relaxed, and did not touch upon possible alternative scenarios. After a general introduction on Dark Matter, White went through all evidences, including the famous Bullet Cluster. One of the points he made was that neutron and neutrino were predicted/invoked well before they were discovered. In particular, the neutrino was postulated in 1930, but confirmed only in 1956. Something similar might be happening for dark matter particles. DM was postulated by F. Zwicky in 1933, but the particle has not been found. At least not yet. For some time there were hopes that the neutrino could be the one, but with the mass limits set for it, there is not much neutrinos can do for DM.

The first slid by Pavel Kroupa (photo courtesy of M. Pawlowski).

The first slide by Pavel Kroupa (photo courtesy of M. Pawlowski). LCDM is ruled out

On the other hand, Pavel Kroupa started in a very bold way. His first slide carried an explicit title: “LCDM is Ruled Out” (LCDM stays for Lambda-Cold Dark Matter, i.e. the most favored cosmological model including cold dark matter and dark energy). The bloggers report that when the slide appeared there was a general laughter in the fully packed seminar room.

The main point made by Pavel is that LCDM does not agree with what we see in the so called local volume. In other words, the predictions of LCDM cosmologies on scales comparable to our neighborhoods (say, less than a million light years), are completely wrong when compared to what we actually see. And this, in Pavel’s opinion, is sufficient to rule out LCDM. Unless, he adds, we live within a very special bubble (which would bring us back to a sort of pre-Copernican age).

While he mentions MOND and MOG as alternative theories, he also touches upon the sociological aspects of the whole matter, and how difficult it is to go against the mainstream (in this respect I like to mention that a few days ago Pavel had written to me asking about the status of our very old stars paper, which you might remember got brutally but superficially rejected by A&A).

During the final debate, Simon White admits that LCDM has some problems, but he also points out that the small scale structure is not a problem at all, as this is complicated by other issues, which cannot be explained by a model that reproduces the large scales. Pavel Kroupa maintains that this is a catastrophe for LCDM (one of the two must probably be wrong, you’d say).

Watching the blog it was very interesting to see how different people reacted (online) to the various statements. Interestingly, a live poll launched by the bloggers on MOND concludes that for 72% of the voters this is a nice theory that needs to be improved. Only 12% thinks it does not make any sense to work on MOND, since we already have LCDM. I was under the impression that the blog audience was biased (probably anti-mainstream or non-aligned people attended the blog more frequently than LCDM-people, who considered it simply not worth).

Certainly an interesting and stimulating afternoon. However, there is a sentence that keept knocking on my mind the whole afternoon: “We do not understand nature. We measure it“. So says my brilliant friend Roberto Siagri. And, from time to time, I think he is right (more than ever when I ponder about astronomy). Think of the simple first law of motion: Every body remains in a state of rest or uniform motion unless it is acted upon by an external unbalanced force. We call it a law, a principle. From this (and other principles) we deduce everything else. The fact that the results are in agreement with what we see lead us to conclude that we understood how nature works. But the principles masquerade the very simple fact that we do not know, for instance, why every body remains in a state of rest or uniform motion […].

Or, for that matter, why two bodies attract each other with a force which is proportional to the product of the masses and bla bla bla. Sure, if you go along this path you will certainly end up asking the famous question why there is something rather than nothing. And, in turn, this will probably lead you/me/us nowhere. However, the fact that we do not know what pulls two bodies together, still remains. And somehow we have to cope with that.

This probably requires some healthy fraction of schizophrenia ;-)

10 Responses to We do not understand nature, we measure it

  1. You don’t show pictures of the debaters themselves, so here is one I took; more – and a detailled report about the event, with links to original papers – will go up in a few hours on my blog. I would say that the Standard Model clearly ‘won’ (White actually presented more aspects where it fits cosmological data than I knew before), but that more work is necessary to fill out the gaps regarding the local Universe. However these simply aren’t the showstoppers Kroupa claims they are: If a model fits the Big Picture so astonishingly well as LambdaCDM does, a failure to explain some details of our – very complex – neighborhood is merely a nuisance (and something to work on for future astronomers). Overall it was a very entertaining afternoon, and it should be worth watching the – almost 2 hours long – full recording.

  2. A summary report in German – with many links to papers cited during the debate or related to it – is now finished.

  3. Nando Patat says:

    I fully agree that the failure of LCDM to reproduce what we see on small scales might be just because the model has not enough “resolution”. After all, our sea tidal theory is able to predict what happens on large scales, but it has problems in reproducing the water behaviour on scales of a few km. Same is true for weather forecast. But in cosmology one has to be watchful, as small failures may betray much larger problems (see the epicycles).
    Also, we should not forget to mention that the Bullet Cluster, which is often (including yesterday) invoked as the final proof of LCDM, might actually contradict LCDM. See this recent paper: http://arxiv.org/abs/1003.0939

  4. Marcel says:

    Thanks for this nice report and for pointing others to our live blog. You helped making it much more successful than we would have thought.

  5. anand srivastava says:

    I was thinking that the Bullet Cluster failure (for LCDM) will be included in the slides by Pavel. I was disappointed on that point.

  6. Nando Patat says:

    The Bullet Cluster failure was indeed quoted at the beginning of Pavel’s talk.

  7. Peter Fred says:

    Nando Patat said, “Or, for that matter, why two bodies attract each other with a force which is proportional to the product of the masses….we do not know what pulls two bodies together… And somehow we have to cope with that. This probably requires some healthy fraction of schizophrenia.”

    Well that is what the the whole kaboodle lot of you are: a rank collection of schizophrenics. You all have been walking around believing in a wrong premise about gravity and acting on that premise every waking day of your professional careers. You all have an unquestioned faith in in the mysterious power of mass to attract other mass. You will not scrutinize or think about what gives mass the ability to attract other mass or warp space. This unquestioned acceptance of an important, far-reaching premise is what a serious obsessive-compulsive will indulge in. While that person is suffering from schizophrenia, he will believe in a premise such as an “irrational fear of germs” and act on that belief for years by scrupulously cleaning and cleaning. And while he is doing all this compulsive behavior he will be hardening his unquestioned premise until it becomes an habitual belief. The last thing you can do with such a person is to tell him he will not become ill if he touches this and that. He will want to jump at you.

    The followers of the Ptolemaic system were not easily told that the basic premise of there beloved geocentric theory was doubtful. They never thought about just how the earth was able to make all the objects in the sky rotate around it in 24 hour period.

    We now know that their hotly-defended belief was based on an ARTIFACT–the fact of the earth rotating on its axis every 24 hours.

    So now I ask you is your hotly-defended, unquestioned belief that mass attracts mass or warps space also based on an ARTIFACT?

    You are all aware that the Stefan-Boltzmann law tells us that if a body has a temperature it has radiation leaving it. Furthermore, you are all aware that the amount of radiation leaving an astrophysical body, just like the gravitational force varies inversely as the square of the distance from that body. So now I hope I have confronted you have a real possible artifact that might make you think about this crystallize belief that mass can attract other mass or warp space.

    If I have this I would hope might want to consider that it may be the luminosity leaving the sun that is attracting the planets and not its mass. (The Tully-Fisher relation, L=k*V^4 sort of tells us that it is the luminosity of a galaxy that is causing the flat rotation curves doesn’t it?).

    Because of the Nichols radiometer studies everyone thinks that radiation is repulsive not attractive. This is too an important of a question to be answered with a radiometer with a high vacuum which in no way mimics astrophysical bodies which generally have an atmosphere.

    I have placed four test masses in between a 1000 W heat source and several copper containers filled with ice. After 4-6 minutes of full power, the observed increase in weight of these test masses was 1.9%, 8.9%, 9.6% and 16% respectively (click my name for my heat-based gravity paper and experiments). The followers of Ptolemaic would not look into Galileo’s telescope to see the phases of Venus. At that is what you will probably do with my experiments. You will not examine them and you will come up with all sorts of Einsteinian “thought experiments” as to why the observed increase in mass could not be right.

  8. Nando Patat says:

    I approved the above comment, so that people can check it out and judge for themselves.

  9. Hi, I read the paper from Peter Fred. I have to congrat him because is an interesting and original experiment that one that he did.

    But I have to propose well known a thermodynamical explanation to his results.

    He only meassures the temperature in the downpart of the copper bowls but has any meassures of the circundant air temperature and is there where the key is.

    The temperature of the air there must have a pronounced gradient becuase we have a heat source down and a heat drain above (the water ice), which should stablish a heat flow upwards through the air. Well, the air below the bowls is near to the heater, so in every moment it has higher temperature that the air above the bowls. As the system is open, the volume is not constant, so classic thermodynamics tell us that the air pressure below the bowls must be lower than the pressure above. So we have also a pressure gradient. Higher pressure above, lower pressure below, means a resultant force pointing downwards,that is, the force meter should note an increasing in the force downwards. That is the usal weight plus additional air pressure downewards due to temperature differences in an open system.

    I think that is the explanation to the effect he describes, although is an interesting effect to show in a class of thermodynamics. If he could provide more data such as air temperature, air pressure, (at least room air temperature and pressure) calculations could be done to see if my thermodynamical explanation matches his results.

  10. Peter Fred says:

    Aitor Robleto
    Thank you for your comments on my weight increase experiments. My experiments and paper mostly get ignored. To me this is just the opposite that should happen given their relevancy to the “extragalactic catastrophe” (i.e the dark matter and dark energy problem).

    My reaction to your proposal that the weight increase was due to a pressure difference, is first of all:

    The observed increase of weight of 1.9%, 8.9%,9.6% and a 16% of objects of 0.5 to 1 kg in mass seems a bit much to be due air pressure differences alone . Secondly, there are two experiments where an 8.9% and the 16% increase in weight was observed where the hot-plate heating element as the actual test mass that was weighed by the force sensor. With the heating element there is not going to be much air temperature difference immediately above and below it. Hence with a heating element, it seems to me difficult for your air pressure difference argument to apply.

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