Astronomy & Physics

"Foo!" to "Are we shortening the Universe's life by observing it?"

sb admin — Sat, 24 Nov 2007 10:16:00 +0000

"Foo!" to "Are we shortening the Universe's life by observing it?"

(I know I'm not doing this any more, but I couldn't resist.)

An article in New Scientist reports on musing by two reasonable and respected cosmologists— indeed, ones whom I've met myself— that our discovery of dark energy may have shortened the life of the Universe.

To which I can only say "foo". And I say "foo" on two levels. Primarily, on the sensational way in which this is described by New Scientist. But secondarily, on the interpretations of quantum mechanics that respectable cosmologists are promoting.

First of all, for a bit of perspective. The actual research paper on which this article is based is available at arxiv.org, from which I will quote the end of the concluding paragraphs:

The second consideration is even more interesting. If observations of quantum mechanical systems reset their clocks, which has been observed for laboratory systems, then by measuring the existence dark energy in our own universe have we reset the quantum mechanical configuration of our own universe so that late time will never be relevant? Put another way, can internal observations of the state of a metastable universe affect its longevity?

They are asking the question.... And what do we get out of "New Scientist"? Cosmologists observing the Universe may have shortened the life of the Universe! Geez.

If this is not an article tailored to feed fuel to the anti-science types who are warning of the dangers of "meddling in that which we do not understand and were not meant to understand," I do not know what was. Now we have a respectable science magazine and two respectable cosmologists on record as saying just looking at the sky could hasten the end of the Universe ZOMG!. And while my quote of the scientific paper above may seem to restore respectability to Krauss and get him off the hook, he does have this sentence quoted in the New Scientist article:

If so, as incredible as it may seem, our detection of dark energy may have reduced the life expectancy of our universe.

The very first thing to keep in mind is that we are taking about timescales of 14 billion years. The Universe may die in 14 billion years instead of 140 billion years because we were so bold as to look at it, if you take the results of this too seriously. So there's no need to worry about the effects this will have on the Christmas shopping season. (Well, unless the article itself raises worries.)

But there are other things to think about before we march to the offices and homes (including mine) of the two teams of astronomers who discovered Dark Energy, and burn them to the ground. Consider this. There are 100 billion stars in our galaxy. There are 100 billion galaxies similar to ours within our observable Universe. We know that planets are ubiquitous in our neighborhood of the galaxy. I will not make any estimation as to whether or not there are other life-bearing, or, more to the point, intelligent life-bearing planets in our region of the Galaxy. But do you really believe that nowhere in this observable Universe there is nobody else out there looking at the skies? I find that simply implausible.

More to the point though... this whole thing is reading too much into quantum mechanics. This is writing in a science magazine (New Scientist) interesting speculation that better belongs in science fiction (cf: Greg Bear's interesting story "Schroedinger's Plague"). I do have to admit that macroscopic consequences of Quantum Mechanics are something potentially very cool. But there are a lot of fuzz-heads out there who like to take things that scientists say about Quantum Mechanics and use it to claim that there some sort of scientific basis to their bogus mysticism (cf: How Much #%*! Can We Spew?). It sort of alarms me to see respected cosmologists quoted in a mainstream science magazine saying things about quantum mechanics that sound like Intelligent Design processed through the most stereotyped of post-modernist "reality is a social construction" deconstructionism.

There is real science behind this. There have been experiments showing the so-called Quantum Zeno Effect (also sometimes called "Quantum Non-Demolition", unless I am mistaken) where a particle's decay time can be delayed by observing it continuously. What happens here is that the particle's "decay clock" is "reset" each time it is observed not to have decayed. I hereby poke Chad to talk more about this, because I suspect he knows a lot more about it than I do.

Is any of this real? In reality, we currently know so little about the true nature of Dark Energy, and so little about the conditions in the early Universe, that this is one of many thoughts that are out there in the theoretical mill being chewed on by people smarter than me. As we stumble our way towards some understanding of quantum gravity, we're going to think a lot of "out there" things, many of which will turn out to have been completely on the wrong path, some of which may surprisingly turn out to be correct. There was a time not too long ago when some of the perfectly well understood consequences of quantum mechanics— e.g. the fact that nature is not deterministic, but stochastic, at its most basic level— seemed utterly nonsensical and impossible. Almost certainly something surprising will come out of quantum gravity. But we're not there yet. So don't become alarmed.

However, I may be proven wrong, but let me go on record as saying that I am deeply dubious that our Universe will turn out to behave as a quantum system in this manner. There is absolutely no doubt that quantum mechanics does have effects on macroscopic systems. Consider blackbody radiation, the spectrum of light we see from something like the Sun. The nature of that spectrum cannot be understood without quantum mechanics (and was one of the leading problems with late-19th-century Physics). However, the fact that you can't explain the shape of the Sun's spectrum without quantum mechanics does not imply that the Sun behaves as a quantum particle whose existence is in doubt when nobody happens to be looking at it. I suspect that the sorts of things we're seeing here are the same kinds of "taking quantum mechanics too far out of its relam" mistakes.

sb admin Sat, 11/24/2007 - 05:16

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Big Bang & Cosmology

Big Bang

quantum non-demolition

quantum zeno

To which I can only say "foo". And I say "foo" on two levels. Primarily, on the sensational way in which this is described by New Scientist.

You expected better?

They think it's their job. No, seriously: an editor told me so, in just about as many words.

To the New Scientist I ask, "What constitutes an observation?"

Dark matter and dark energy are so tied to the dynamics of galaxies, including our own, that even looking at the sky at any point would cause the kind of collapse they're talking about, a la Schroedinger. Even if we aren't aware of it, we can look up at the night sky and have our retinas bombarded by photons emitted by distant quasars and clusters of galaxies. Isn't that an observation? Or do we have to be cognizant of the fact that we're indirectly observing dark matter and dark energy whenever we look at anything? An affirmative answer to that question doesn't make any sense, and if we answer no we have to ask what makes the interaction of a photon with our retinas more important than the interaction of dark matter with a galaxy. I don't think it is any more important.

I think it was Heisenberg who suggested that we'd ought to adopt the word "interaction" rather than "observation". I'm sure that if we take that kind of view through to its conclusion, we arrive at something like the relational quantum mechanics described by Smolin, Rovelli, et al. The blogosphere seems to be populated by many-worlders and ensemble supporters, so I'll probably be run off with torches and pitchforks for saying it, but there isn't, as far as I know, any room at all for looking at the universe as having a wavefunction within the scope of relational quantum mechanics. I don't think we have to wait for quantum gravity at all to say that it's doubtful that the universe will display the kind of quantum behavior the New Scientist is suggesting it does.

Dear Rob

This is another typically excellent post. I'm glad that you have (tenatively) returned to science blogging. Your ability to communicate is refreshing.

Unfortunately, quantum mechanics is being bastardised by all sorts of mystic-merchants, creationists, Intelligent Designers (read ignoramuses) and other assorted galahs to promote a pseudo-spiritual, faith-based ideology.

Keep blogging and Vanderbilt will realise that they have lost a talented scientist.

Cheers from Sydney, Australia

As a dedicated layman, I could only laugh when I heard this news. As you know the mechanics I'm best at are brakes on Mustangs - but the whole thing sounded to me like a movie reviewer was writing about this instead of a Scientist.
Thanks for you comments.
GJJ

Supernovae: the source of cosmic rays

sb admin — Wed, 10 Oct 2007 16:50:00 +0000

Supernovae: the source of cosmic rays

Astronomers have long assumed that supernovae are the source of at least most of the cosmic rays that hit Earth.

Woah, slow down... cosmic rays? Right, you hear the term all the time, but do you really know what they are? They are charged particles that rain down on Earth from space. Really! Kinda cool, huh? There are charged particles— mostly protons, or hydrogen nuclei, but with some heavier ions mixed in— smacking into our atmosphere all the time. Some of them have extremely high energies, higher energies than those to which we can accelerate particles in our best particle physics accelerators. Of course, the very highest energy cosmic rays are the rarest.

Thanks to a recent study by the Chandra Space Telescope, we have direct confirmation of the model that cosmic rays are produced in supernovae.

In fact, the Solar System is awash in charged particles, many of which come streaming off of the Sun. A "cosmic ray" proper, however, has a higher energy than most of the particles coming off of the Sun, and comes from outside the Solar System. The production mechanism for these cosmic rays is called the "Fermi mechanism," and involves compressing magnetic fields in supernova remnants.

The path of a moving charged particle will be bent in the presence of a magnetic field. Indeed, magnetic fields can "capture" moving charged particles (both from the Solar wind and cosmic rays), causing them to spiral about it. We have bands of charged particles, the so-called "Van Allen Belts", around the Earth; these are particles trapped in the Earth's magnetic field. As the particles spiral along the fields, they crash into the atmosphere near the North and South Poles, where the magnetic field lines dip down into the earth. The result of the collisions of these particles with the atmosphere is what can be seen on earth as aurorae.

Supernova remnants have two things. First, they have strong magnetic fields; we've known this for a long time. Second, they have expanding gasses. In general, if you have a gas whose particles are partly charged, magnetic fields will move along with the gas. As the high-velocity gas in a supernova expands into the interstellar gas around it, you get shocks where the expanding gas collides with the ambient gas. You will also have magnetic field lines getting compressed, as the magnetic fields in the expanding gas plow in to the ambient magnetic fields out there.

Charged particles moving about the field lines of expanding gas will bounce back and forth between the expanding magnetic fields and the ambient magnetic fields. As the two field lines come closer together, the magnetic fields pick up energy. It's similar to bouncing a tennis ball between two trucks coming towards each other. Each time the tennis ball collides with one track and bounces back towards the other, it picks up a bit of the kinetic energy of the oncoming truck, getting faster and faster and faster.

Normally, the charged particle would stay trapped in these strengthening magnetic fields (the compressing magnetic field lines) forever. However, there is enough junk there that eventually the charged particle— potentially moving quite fast now— will bounce off of something and get scattered out of the supernova remnant. At that point, it goes flying through the Galaxy as a cosmic ray.

The new observations show hot spots in X-rays appearing and disappearing in the shocks at the edge of a supernova remnant, which results from the sporadic production and release of the charged particles, some fraction of which will run into planets and be observed by the residents there as cosmic rays.

(Hat tip: Roger Amdahl of the Second Life "Astro News" group.)

sb admin Wed, 10/10/2007 - 12:50

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Astronomy & Physics

Astronomy Science

Any guesses as to what fraction of the high energy (say >1GEV) may be coming from other sources? Things like Neutron stars, magnetars, less violent stellar outbursts, collisions of gas clouds ...

Nice result, but I have a couple of nits to pick.

First, these are presumably the "Galactic Cosmic Rays" (GCRs). There are other cosmic rays, mostly of lower energy, which are produced from accelerating solar wind particles at the heliospheric termination shock, by a similar mechanism as you describe for the GCRs. The highest energy cosmic rays (above ~10^12 eV) are of extragalactic origin.

The other point happens to be my area of expertise:

We have bands of charged particles, the so-called "Van Allen Belts", around the Earth; these are particles trapped in the Earth's magnetic field. As the particles spiral along the fields, they crash into the atmosphere near the North and South Poles, where the magnetic field lines dip down into the earth. The result of the collisions of these particles with the atmosphere is what can be seen on earth as aurorae.

The problem is with the last sentence. The particles that cause aurorae are not the radiation belt particles (which include electrons of 1-10 MeV and ions of >10 MeV/q) but rather 1-10 keV electrons which are accelerated a few thousand km above the Earth's surface. The latter are much more numerous, and they deposit their energy at higher altitudes where "forbidden" oxygen transitions (particularly the 557.7 nm line which is the green of the aurora) can take place. The radiation belt particles contribute to the airglow, but much less because there are relatively few precipitating particles at those energies.

The best site I know of for the basics of magnetospheric physics is the online textbook at Oulo University (http://www.oulu.fi/~spaceweb/textbook/). Oulo is in northern Finland, far enough north that aurorae are visible most clear nights (at least from September to April when midnight sun is not an issue).

It's been a couple of years since I've checked, but re: the extragalactic cosmic rays, has a GZK cutoff been observed? There has been this problem with the very highest-energy comsic rays that they have enough energy relative to the local CMB background photons that the Universe is "optically" thick (electronically thick?) to them, and they shouldn't be able to travel very far-- limiting potential extragalactic sources of those CRs.

re: the extragalactic cosmic rays, has a GZK cutoff been observed?

The latest I've heard was a year or two ago at a department colloquium. At the time there was evidence of a GZK cutoff, but it wasn't yet a slam dunk. Apparently some earlier studies failed to see the cutoff. It's hard to tell because fluxes are so low (<1 particle per km^2 per year) at the relevant energies, whether or not the cutoff is there.

Mr Lund or Dr Knop, can you please clarify "forbidden" transitions for me (i.e. as opposed to "allowed" ones, and why the "forbidden" ones are "permitted" in the aurora)?

There are various mechanisms by which there can be a transition between two quantum states in an atom. The most likely transitions go by an "electric dipole" transition. There are various "selection rules," but ultimate it has to do with the difference in the quantum numbers of the two states: the spin of the electrons, the orbital angular momentum, the total angular momentum, the z-component of the angular momentum, etc.

"Permitted" transitions are transitions that have a strong coupling between the two states. As such, they have a very high transition rate, or equivalently, the upper state has a very low lifetime.

A "forbidden" transition does *not* have an electric dipole transition; it is "forbidden" by the selection rules. However, there are other kinds of transitions -- magnetic dipole, electric quadrapole, etc. They *can* happen, but the probability (thus the transition rate) is much lower, and thus the lifetime of the state is much higher.

In a high density gas-- a gas such as is found in gas vapor tubes we make on Earth-- the lifetime of these "forbidden" states is so long that a collision with another atom or electron is very likely to happen before the photon-emitting transition has time to happen. As such, that transition is more likely to be collisionally de-excited than radiatively de-excited, and we never see the radition from it.

However, many astronomical gases are so low density that the time between collisions can be longer than the lifetimes of these "forbidden" transitions, so we *do* see the radiation from these forbidden transitions.

In other words, they're not the most probable transitions, and they are forbidden *to first order*-- and we don't observe them in the lab because other things cause the atom to leave the state before it can radiatively decay. In environments that are much lower density than what we observe in the lab, though, these "forbidden" transitions really do happen.

Actually Oulo is quite a way south of the quiet-time Auroral Arc (the location of where aurora occurs most days). We work with the VLF group in Sodankyla (maybe 300 km further north and they are part of a geophysical observatory run by the Oulu University) and I have been lucky enough to get there for a workshop (long way from my home in New Zealand), out of the two weeks I was there we had maybe 2 nights of aurora (which I missed - but I am going on reports of the rest of the people from the workshop), you normally have to go further north to Norway to get it more often (and even then it was too cloudy for me to see anything)

But I agree with what you said about the space physics textbook very worthwhile if you need information about this sutff.

Robert

Answering Objections to the Big Bang

sb admin — Thu, 27 Sep 2007 21:34:20 +0000

Answering Objections to the Big Bang

Every so often you will come across somebody who has a "killer" list
of "problems" with the Big Bang. While there remain unknowns and
questions about the Big Bang— just as there do with biological
evolution— the basic picture of the Big Bang is rock
solid— just like evolution.

Nearly two months ago, I received a query from somebody who found my
name through the
Clergy
Letter Project "expert database" regarding one of the websites that
lists these objects. I've been through quite a number of life changes
in the last 6-8 weeks, and my blogging rate has suffered as a result.
However, I'm finally getting to it. Nearly all of the things I will
respond to here are generic responses, as these "objections" to the
Big Bang are frequently brought up, but for reference I will link to
the site that was given to
me: Dr. Tom
van Flandern's Top 30 Problems with the Big Bang. Nearly all of
these objects are either a misunderstanding of the Big Bang, or
an objection that is out of date. I won't address all 30
individually, but I will hit some of the highlights. The fact
that I don't address a given objection should not be taken as
evidence that I'm ceding the point!

Objection 1 : Bad Fits to Data

The first objection I will quote in its entirety, because not only
does it contain false information, but it contains a more general
canard that is often used when objecting to scientific theories:

(1) Static universe models fit observational data better than expanding universe models.

Static universe models match most observations with no adjustable
parameters. The Big Bang can match each of the critical observations,
but only with adjustable parameters, one of which (the cosmic
deceleration parameter) requires mutually exclusive values to match
different tests. [[2],[3]] Without ad hoc theorizing, this point alone
falsifies the Big Bang. Even if the discrepancy could be explained,
Occam's razor favors the model with fewer adjustable parameters [than]
the static universe model.

This is incorrect on several fronts. First of all, we get very good
and precise fits from the Big Bang model. Additionally, the "cosmic
deceleration parameter" turns out to be negative. It was true 10
years ago that different lines of reasoning suggested different
values for this parameter, but the truth was that we really hadn't
been able to make a good measurement of it. Now we have, and
the acceleration of the Universe fits with sundry lines of
reasoning— so much so that now have what is frequently called
"standard model" of cosmology, or a "concordance cosmology", with the
various parameters (expansion rate, overall density, dark energy
density, age of the Universe, etc.) measured each to within 5%. This
agreement is now nearly a decade
old; here
is a link to a 1999 Science abstract about the concordance,
and here is a link
to a preprint site that has the full text.

This objection also points out something that I will probably devote
an entire post to in the future: a misuse of Occam's Razor. Too often
people object to a scientific theory on the basis that they have a
"simpler" theory which must be favored because of Occam's Razor.

Objections 2 and 3: the CMB and Element Abundances aren't fit
well

Both of these are quite wrong. Indeed, the cosmic microwave
background is well-fit in detail in the Big Bang model;
consider, for example, the recent(ish) WMAP 3-year results
(paper,
press release and pretty
pictures.) Likewise, we do achieve consistency in Big Bang
Nucleosynthesis models with observed element abundances, given
uncertainties in the measurements. The number of adjustable
parameters needed to match this consistency is in fact not very large,
but I'll address that later.

Objections 4: Too much large-scale structure

In fact, detailed structure formation models starting from the
perturbations seen from the Cosmic Microwave Background (which is
300-400 thousand years after the Big Bang) and propagating forward to
today do an amazingly good job of predicting the very largest scale
structure. We do have filaments and voids. Both of the two new
astronomy professors at
Vanderbilt, Kelly
Holley-Bochelmann and Andreas Berlind, are experts on this. It
was, I believe, in Andreas' job talk where he showed us two maps: one
was an astronomical survey, the other was from calculations. He
challenged us to tell him which was the data, which was the model; of
course, we couldn't.

Objection 6: The ages of globular clusters appear older than the
universe.

This objection is simply 10 years out of date. Yes, it was true 10
years ago that there was a cosmological "age crisis." The most
plausible models of the Universe seemed to favor a Universe that was
less than 10 billion years old, whereas the oldest globular clusters
were observed to be 12-13 billion years old.

Today, there is no conflict. The major change was the discovery of
the accelerating Universe. The addition of dark energy affects the
age estimates we get in the Big Bang model, and now we have a
measurement of the age of the Universe that is 13.6 billion years,
good to about 5%... and no longer in any conflict with age data from
globular clusters.

Objection 8: Invisible dark matter of an unknown but non-baryonic
nature must be the dominant ingredient of the entire universe.

And?

I mean, yes, this is true. This is one of the big mysteries in
cosmology (and, perhaps particle physics) right now. What is Dark
Matter? The fact that it is there (and, we know it is there; see
also these
slides from a talk I gave back at an astronomy journal club back
when I was still a professor at Vanderbilt).

The website brings up Milgrom's "MOND", which was originally put
forward as an alternative to dark matter to explain galaxy dynamics.
However, the aforelinked results from the Bullet Cluster have shown
beyond a doubt that there is matter in the Universe that is not
where baryonic matter is. Exotic Dark Matter exists. We know that,
independent of any considerations involving modelling the Big Bang.

Objection 10: The open Universe requires extreme fine tuning

This one has gone away, but the whole issue of "cosmological fine
tuning" hasn't; that remains an outstanding question in the Big
Bang.

However, once again this website is about 10 years out of date by
referring to the "open" Universe. Current cosmic microwave background
data favors a flat Universe, and has since about 1998 or 1999. What's
more, the most recent WMAP results linked above provide support for
the "inflation" scenario that explains why the Universe should be so
close to exactly the critical density needed to make it flat.

Etc.

There is other misinformation in the article. For instance, it
mentions quantized redshifts, which are something that's been
suggested by data in the past, but which is no longer believed to be
true. Given the filamentary nature of the Universe, if you take a
"pencil-beam" survey you will observe what appears to be quantized
redshifts, because your pencil beam will go through voids. We now have
enough large-area surveys to see the full large-scale structure, and
see the shape of those voids (and the aforementioned success in
modelling them) to understand why pencil-beam surveys sometimes
appeared to indicate quantized redshifts. The First Law of
Thermodynamics is mentioned, but just as with almost every other time
somebody uses a law of thermodynamics to argue against a well-accepted
theory (and you know what I'm talking about here), it represents a
misunderstanding of thermodynamics.

For other detailed complaints, where I don't have the answer off of
the top of my head, it would take me more work to really address it.
However, the major points are addressed above. Overall, the
objections in that web page— which summarize most of the
objections one usually sees to the Big Bang— are either flatly
incorrect, are out of date, or are outstanding questions that remain
to be answered but do not invalidate the overall picture of the Big
Bang.

Yes, questions remain! That's part of what's exciting about it. But
the overall picture of the Big Bang is supported now by a wealth of
observations, models, theory, and comparison between the three. As I
noted in my classic post "Big Bang" is a
terrible name for a great theory, we don't really
know anything about the moment of "Bang" itself... hence the
name of the theory not being so great. But the overall picture of a
homogeneous and isotropic (on large scales) Universe that has expanded
from an extremely hot and dense state is what all of the data point
to.

sb admin Thu, 09/27/2007 - 17:34

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Back with a bang :o)

Nice to see you posting again.

He makes an interesting point about the phenomenological MOND model being better than the more fundamental dark matter model because the prior doesn't have "fudge factors." Science would be a lot simpler if we replaced these complex, detailed theoretical models that have all sorts of parameters to measure with simple phenomenological models that have few or no parameters to fit! I mean, we may only be able to describe what happens and no longer why and how something happens, but who really cares about details?

Along those lines, I propose a new model of the Sun. I propose that it is basically a hot object, so that it throws off blackbody radiation and looks bright. Also, it emits neutrinos. But since it is a descriptive model and doesn't delve into explanatory details like invoking hydrogen fusion, the CNO cycle, etc., it is immune to all the problems with the Standard Solar Model, like incorrect ratios of neutrinos. By inserting adhoc assertions like neutrinos oscillate (particles with mass? Get real!), the Standard Solar Model gets complicated. By not even addressing neutrino masses, my model doesn't require them to be massive (but it allows for that to be the case), so is much simpler. Therefore, by Occam's Razor, my model is better. I'll now be waiting by the phone for that call from Stockholm.

Seriously, you cannot discount a fundamental model in favor of a phenomenological model simply because it has parameters that must be fit. For all you know, the underlying theoretical model that is the basis for the phenomenological model will have ten times as many parameters to fit.

CS -- yeah, good point.

The truth is that even just a few years ago, the observation evidence on galaxies didn't really strongly favor dark matter or MOND. Most scientists preferred dark matter because it fit a lot of other things, and because until Beckenstein, MOND really was purely phenominological.

But, now, yeah, we know there is dark matter. Kinda cool how science can advance :)

Nice to see you back.

So the present thought is that the universe will expand forever as a consequence of flatness, with the "big crunch" idea out of date? (There was a "big crunch" theory at one time, wasn't there, or did I maybe just get that "end of the universe" stuff from watching too many episodes of Dr. Who?)

JuliaL -- yes, sort of. The high probability that the Universe will expand forever is in fact not a consequence of flatness, and isn't even linked to that any more.

Before 1998, most cosmology textbooks would draw the connection between geometry and fate. A closed (spatially finite) Universe would recollapse in a Big Crunch, a flat or open Universe would expand forever. However, the connection between these two requires the assumption of no cosmological constant (i.e. no dark energy). With dark energy, it's possible to have a closed Universe that will expand forever.

So, yes, we think that the Universe will expand forever, and there never will be a Big Crunch. But that's not a consequence of flatness, it's a consequence of dark energy. The supernova results themselves pointed towards an accelerating Universe that would expand forever, but didn't provide any constraints at all on open vs. flat vs. closed geometry. The flat geometry constraints were provided by the Cosmic Microwave Background— but at least the first measurements of flatness (from BOOMERANG AND MAXIMA) didn't provide strong constraints on expand forever vs. Big Crunch, at least if you took the possibility of dark energy int account.

What do you feel about the Arp associations?

For example, there is a physical connection between the barred spiral galaxy NGC 4319 and the quasar like object Markarian 205. This connection is between two objects that have vastly different redshift values.

Mike -- that's a whole 'nuther post. ;D One year I will hopefully get to it.

Dark matter is constructed as a hypothetical explanation to help the misinterpretation of the galaxies' rotation curve where the angular velocity is mixed up with the orbital speed.

Big bang is a misinterpretation of the fractional displacement of the radiation that is an entropy-effect which causes the energy to move towards equilibrium.

No dark matter is needed.
No dark energy is needed.
No Big Bang is needed.

Ingvar, Sweden
http://www.theuniphysics.info

Why most of Astronomy isn't Cosmology

sb admin — Sat, 18 Aug 2007 07:15:00 +0000

Why most of Astronomy isn't Cosmology

This is mostly just an MLP ("Mindless Link Post"), and it's nearly two weeks late, but there's a post by Julianne over at Cosmic Variance that I think is of crucial importance. People who are outside the field of science very often lose sight of the huge amount of important science that is done, but doesn't produce the "amazingly sexy discovery" news headlines, or, say, the Gruber prize. Also, people working in one field of science often don't appreciate the value of other fields of science when it doesn't obviously overlap theirs... even though, as Julianne points out, all of that other "uninteresting" stuff may well have included things necessary to generate the bits that overlap their field!

In one of my first years at Vanderbilt (back in the days when I used to be a professor), one of the older experimental particle physicists came into my office, wondering why we were talking about supporting all the other boring star-and-planet formation science being done, when I was the only astronomer doing anything "really fundamental." (I was still working in supernova cosmology at the time.) One of these other astronomers was David Weintraub, not then but now the author of a successful popular science book Is Pluto a Planet?— a topic that would be hard to argue has no general interest. David was and is working on things that addressed the formation of our own Solar System, something which was not only one of the current hot and sexy topics in Astronomy, but which is easily of as much "basic human interest" as the origin of our Universe, and more immediate (so to speak) and tangible besides! This particle physicist nodded, indicating surprise, saying that I had a good point that different people might think different things are of the most basic interest.

It's easy to find particle physicists who think that cosmology is the only thing in astronomy even vaguely of interest. (Just as it's easy to find atomic and solid state physicists who think that particle physics is useless musing whose valuable period ended well before the 20th century, and just as it is easy to find astronomers who think that cosmology is all poorly-grounded crap that represents only borderline interesting science, and is mostly a land grab by particle physicists interested in astronomy funding sources.) There really are two things here. First is the fact that there is an awful lot of interesting science out that that people in your field genuinely have no reason to care about. Second, though, and this is something that as an astronomer as frustrated me watching particle physicists come in and think they know how to use telescopes: people outside of your field know a lot of things about how to do their science that you don't know, and you dismiss them at your peril. Julianne says it best:

...if you limit astronomers' ability to go forth and characterize what the universe is actually like, no one will be laying the foundations for the next generation of crazy-physics-you-can-study-in-space. For astrophysics, the Universe is our LHC, and we've got to be free to characterize our widgets, even if they're boring ole brown dwarfs rather than panels of supercooled silicon wafers.

sb admin Sat, 08/18/2007 - 03:15

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Astronomy & Physics

Astronomy Science

The Business of Astronomy

Second Life Q&A on the Accelerating Universe

sb admin — Tue, 14 Aug 2007 20:32:00 +0000

Second Life Q&A on the Accelerating Universe

Following the talk I gave in Second Life about the discovery of the accelerating Universe, we held a couple of Q&A sessions. The original plan was to have questions right after the talk, but the Second Life main grid crashed right at that moment. We all got online about half an hour later, and I held one Q&A session for the people who came back. There was another one the next day.

Troy McLuhan (his Second Life avatar name) logged the session, and has done the hard work of formatting and lightly editing it for web publication. You can find the transcript of the Q&A session online here.

sb admin Tue, 08/14/2007 - 16:32

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Well done, Rob Knop. And good transcribing, Troy McLuhan.

I read it all, both as a former Adjunct prtofessor of Astronomy, and someone who's recently taught energetic highschoolers. It reminded me of caltech symposia for the public, or for families of alumni, where I know all the content, but appreciate the clarity of exposition, the good teaching, and the feedback from the audience.

Kudos all around.

Interesting reading (still on going)

[10:18] ToolsRMe Shan: So as the galaxies move further and faster apart, at some point they will exceed the speed of light. At some point in the distant future, our galaxy will be alone. Is that current theory still?
[10:18] Prospero Frobozz: ToolsRMe Shan: sort of.

[10:18] Prospero Frobozz: In fact, its not just our galaxy, but the local supercluster of galaxies that are still bound together.
[10:18] Prospero Frobozz: So well stay together with our nearest neighbors.
[10:18] Prospero Frobozz: But other than that, yes, as the expansion of the Universe gets faster and faster, eventually there will be this lonely isolated group of galaxies thats all we can see.

[10:19] Prospero Frobozz: Quanta: Yes, pretty much :) Except that its a big island. Our galaxy alone has a hundred billion stars.

So basically visible matter (the stuff galaxies are made of) is like a drop of grease (oil) in a baloon. The baloon expands, the grease disperses into globules - but there is never more grease, just more volume.

However Rob, are we not just playing with Russian Dolls again ... the universe expands eternally into infinity. Literally a beginning with no end.

But if there is (was) a beginning or big bang, Lee Smolin will insist that it came from somewhere and that we are merely a sister (or parallel) universe, and that there may be other sister (or parallel) universes created along the way - through any one of the blackholes in the galaxies...

And dare I say, Susskind would insist that we are just one of the universes in a lanscape of multiverses ... and hwever this dark energy (and gravity) interacts with this observable Universe IS where the 'crux' of the matter is.

And you or someone (like I) could postulate that from all possible universes in the multiverse finally emerges one, let us hope it is the one we are in, though few things outside a four score years time frame are ultimately really material to any of us - except of course to speculate or theorize on the physics & maths of the universe around us.

Accelerating Universe Talk Transcript & Followup

sb admin — Tue, 31 Jul 2007 13:39:00 +0000

Accelerating Universe Talk Transcript & Followup

I managed to get through my 15-20 minute "talk," and just as I threw it open for questions Second Life had a database problem and everbody in-world had to be logged out.... We got back in 40 minutes or so later, and I answered questions for a while for people who came back. However, if you were at the talk and wanted to ask questions but didn't come back, I'll be doing a follow-up Q&A session tomorrow (Wednesday August 1) at 10AM PDT at the same location.

Below, I've got a transcript of the talk I gave. Other than fixing some typos and merging things into paragraphs, I haven't edited what I said/typed.

What I want to do is spend about 15 minutes going over these slides I
have hanging around the room. I've given 70 minute talks on this stuff
before and still had more to talk about, so obviously this isn't
everything :). What I'll try to do is explain how we actually *measure*
the expansion history of the Universe, which is the evidence that led us
to believe that the Universe is accelerating.

First, though, a few brief words about myself, and then a few brief
words on SL training. I got my PhD from Caltech in 1997, although I had
basically finished all the work in Fall 1996. I worked on infrared
spectroscopy of active galactic nuclei. It was when I went on to my
post-doc that I started working on the Universe as a whole. I worked
with Saul Perlmutter and the Supernova Cosmology Project at Lawrence
Berkeley Lab. It was an exciting time to be there, for it was in 1998
that we and our competitors both announced data that showed that the
Universe was accelerating. This has been one of the truly exciting
discoveries in Cosmology in recent decades. Not *quite* as exciting as
the data from the 1960's that confirmed the Big Bang, but it's getting
up there. This has also excited a lot of the particle physics
community, because for the Universe to accelerate, it must be filled
with something-- that we call Dark Energy-- that is not in the standard
model of particle physics.

So what I'll do now is talk about how one actually goes about measuring
the expansion of the Universe, and figuring out that the expansion is
accelerating. First, though, I want to make sure that people know how
to zoom in on the slides I have. I just highlighted one side -- the
border on the side is a lighter color. If you're sitting, you can use
the rotate left and rotate right buttons (A and D) to look around and
find it. Move your mouse over the highlighted slide, hold ALT, click
and hold the left mouse button, and you can zoom in on the slide. (By
moving the mouse.) The writing is too small to read from where you're
sitting, but if you do that you should be able to read it. Is anybody
having trouble reading the slide with the highlighted border?

Measuring distances in astronomy is really hard. There aren't tape
measures long enough to measure the distances between stars.... As
such, there are a whole slew of methods for measuring distances, and
sometimes they come with huge uncertainties. One of the most reliable
is the "method of standard candles," which this slide
outlines. Conceptually, it's very simple. Basically, you find something
whose luminosity -- the intrinsic amount of light it puts out -- is
known. Then, from how bright it is, you can figure out how far away it
is.

On this slide, I've go two candles -- although a 100W lightbulb might
be a better example, because two 100W lightbulbs from the same
manufacturer will put out the same amount of light. The dimmer one is
farther away-- and we can quantify that. The standard candle we used
for the accelerating universe work was a Supernova.

Everybody press ESC to reset your view ;) Hanging in the middle of the
room is a "Nova/Supernova Progenitor."

There's a big red star that's bulged out on one side. Orbiting around
the star is a white dwarf. The big red star is perhaps 100 to 1000
times the radius of the Sun. The white dwarf is no bigger than the
Earth. The gravity of the white dwarf pulls some of the outer layers
off of the red star, which goes into an "accretion disk" swirling around
the white dwarf.

As material builds up on the white dwarf, it reaches a critical mass
where it suddenly explodes and completely disrupts itself in a massive
thermonuclear explosion. Each time one of these puppies explode, they
put out pretty close to the same amount of energy. They are also, for a
few weeks, as bright as a whole galaxy. Thus, we can see them very far
away. These are the standard candles we've used.

Move on to the next slide i've highlighted.

Astronomers have a time machine-- and, indeed, our time machine is way
better than the one geologists and paleontologists have :). Because
light moves at a well-known finite speed, if you see something far away,
you are seeing it as it was in the past. However long the light took to
reach you, that's how far in the past you're seeing it.

When you go outside and look at the sun -- not a good idea, by the
way, if you don't want to go blind -- you aren't seeing it as it is
right now, you're seeing it as it was 8 minutes ago. The discovery of
the accelerating Universe was based on supernovae that exploded as much
as 8 or 9 billion years ago. Because we can measure the distance using
the method of standard candles, we can also measure exactly how far back
in time we're looking.

That's the first piece of the puzzle. The second thing we want to
measure is just how much the Universe has expanded since them time of
the explosion.

Move on to the next (now highlighted) slide.

Again, hold ALT, move the mouse over the slide, and hold the left mouse
button to zoom in. Many of you have probably heard of redshift --
probably because of the Doppler shift. Something that is moving away
from us will show a redshift -- light (or sound) emitted by it will be
shifted to longer wavelengths. Often, the redshift from the expansion
of the Universe is described this way, but in fact that's not really
what it is. In fact, the dynamics of the Universe as described by
Einstein's General Relativity tell us that as the Universe expands,
wavelengths of light expand at *exactly the same rate*. This is called
the "cosmological redshift".

In the diagram at the bottom of the slide, at "Time of emission" there
are two galaxies; we are the one on the right, and the one we want to
observe is on the left. At emission time, some light is emitted. Time
passes, the light travels, and the Universe expands. By the time the
light reaches us, the Universe has expanded -- so the galaxies are
farther apart -- and the light's wavelength has also expanded; longer
wavelength light is redder. The amount of the redshift we observe is a
*direct* measure of how much the Universe has expanded.

Go to the next slide, on the other side of the mollusk... :) [Edit
added to transcript: The mollusk was Joshua Linden.]

The two things I've told you give us everything we need to measure the
expansion history of the Universe. Measure the distance of a standard
candle to figure out how far back in time we're looking; that's the X
coordinate of a point on the graph. Measure the redshift to figure out
how much the Universe has expanded since that time; you can use that to
figure out the relative size of the Universe at the time of emission as
compared to now. That relative size is the Y coordinate of each point.
Plot all your points for supernovae at different distances -- that is,
different lookback times -- and you have your expansion history.

At that point, we can compare it to what theory predicts. On the next
slides are the predictions from theory that we *thought* we were going
to be comparing to when the project was started in the 1990's.

Basically, mass creates gravity; all the galaxies are pulling towards
each other, which will tend to put the brakes on the expansion. If
there is a *lot* of mass, there's a lot of gravity, so the expansion
will be slowing down a lot. In that case, there may be enough mass to
stop the expansion and cause the Universe to recollapse. On the other
hand, if there isn't very much mass (the "low-mass" Universe), the
expansion should be slowing down less, and the expansion will continue
forever. However, because gravity is attractive, no matter what you
should expect the expansion to be *slowing down*-- decelerating.

Go to the last slide.

Again, hold ALT, move the mouse over the slide, push and hold the LMB,
and move the mouse. When we really made the measurement, we can up with
the result that was unexpected by most of us.... For the last 6 or 7
billion years, the expansion of the Universe has been *speeding up*.

A lot of people didn't believe this at first. One prominent theorist,
Rocky Kolb, apparently said in one talk that "the Supernova people had
better figure out what is wrong with their data, or somebody is going to
get hurt." However, there were two independent teams that came up with
the same result, so people took it seriously. Now, almost a decade
later, independent methods have confirmed that it seems that the
accelerating Universe measurement is correct.

Because gravity is attractive, normal stuff can't make this happen. For
the Universe's expansion to be accelerating, there must be *something
else* in the Universe. It turns out that Einstein's General Relativity
*does* allow for a very exotic material which will have (effectively) a
negative gravitational effect. Today we call that Dark Energy. From the
fact that the Universe's expansion is accelerating, we know that Dark
Energy makes up 2/3 to 3/4 of the total energy density of the Universe.

Wacky stuff.

The big slide over the DJ's stage summarizes some of this again, and
shows a bunch of the actual supernova data that I worked on back in
1996-1999 (and may also include some additional data form a 2003 paper I
wrote -- I'm not sure).

At any rate, I'll stop there -- that's the whirlwind tour of just how
one goes about measuring the expansion history of the Universe.

For the rest of the time we have, I'd be happy to answer questions about
any of this, or about the discovery.

...and right then was when the grid crashed. I couldn't have timed it better if I tried.

If you didn't come back at about 11AM PDT to ask questions, drop by the same spot tomorrow at 10AM for a Q&A.

sb admin Tue, 07/31/2007 - 09:39

Tags

Astronomy & Physics

Astronomy Science

Big Bang & Cosmology

Science Education & Outreach

Second Life

If only you could make a supernova progenitor hang in the middle of the room at a real talk...

Fun stuff...thanks for posting it!

Sadly, even when I try to use this fairly simple explanation for why we think the universe is expanding, my evangelical girlfriend looks at me like I'm crazy and says something akin to "that's ridiculous and so is the big bang."

...so ask her which was made first, the people or the animals? Then go read the first two chapters of Genesis....

Astronomy & Physics

"Foo!" to "Are we shortening the Universe's life by observing it?"

Supernovae: the source of cosmic rays

Answering Objections to the Big Bang

Objection 1 : Bad Fits to Data

Objections 2 and 3: the CMB and Element Abundances aren't fit well

Objections 4: Too much large-scale structure

Objection 6: The ages of globular clusters appear older than the universe.

Objection 8: Invisible dark matter of an unknown but non-baryonic nature must be the dominant ingredient of the entire universe.

Objection 10: The open Universe requires extreme fine tuning

Etc.

Why most of Astronomy isn't Cosmology

Second Life Q&A on the Accelerating Universe

Accelerating Universe Talk Transcript & Followup

Objections 2 and 3: the CMB and Element Abundances aren't fit
well

Objection 6: The ages of globular clusters appear older than the
universe.

Objection 8: Invisible dark matter of an unknown but non-baryonic
nature must be the dominant ingredient of the entire universe.