Speed of light

[Chris Peterson]

What do you guys think of this answer:
http://wiki.answers.com/Q/What_is_the_r ... d_distance

Seriously flawed.

[apodman]

Flawed in multiple ways. Might make a good quiz for high school students: "What is wrong with this theory? Show three things wrong with it. You have five minutes."

It looks like someone took one day of Physics and thought they had enough information to wing it and describe anything. My parents told me that when I was two years old I thought Scotch tape could repair anything. Kinda similar sophistication in thought, only I grew up a little since then.

And people complain about the wikipedia as a reference. At least you get some truth there. But this is an excellent example of why nobody should trust any answer they get from any of the "ask anyone" sites on the web. In my experience, every answer I have seen on all of these sites (whether it's wiki answers or one of the others) is completely worthless. And you click on the "recommend contributor" link, and instead of letting you rate the answer poorly as it should be rated, it just adds one more to its "contributor trust" score and thanks you. Amateur from top to bottom.

[Chris Peterson]

But this is an excellent example of why nobody should trust any answer they get from any of the "ask anyone" sites on the web. In my experience, every answer I have seen on all of these sites (whether it's wiki answers or one of the others) is completely worthless. And you click on the "recommend contributor" link, and instead of letting you rate the answer poorly as it should be rated, it just adds one more to its "contributor trust" score and thanks you. Amateur from top to bottom.

Agreed, this site has some serious problems. I have occasionally gotten good information from sites like this, but you really need to be able to judge the quality before you go there. So for most people, it's worse then nothing at all.

There are some good "ask a scientist" sites out there, however. These utilize vetted experts, and questions are directed specifically to the right ones. I've been answering questions about astronomy, meteoritics, and Earth science at madsci.org for several years now. And I've looked at the answers given by others (not in my field), and they seem consistently very good. There are a few "ask an astronomer" sites at various universities as well, which do a good job. You'd not find a response about redshift like this one at any of those sites!

[apodman]

madsci.org

Thanks for the link. It sure beats fishing in a pond where there are no fish.

[harry]

G'dafrom the land of ozzzzz

This paper goes back to 2003

Still quite interesting.

Latest Sun Flare Put at X28, Strongest on Record
SPACE.com -- Latest Sun Flare Put at X28, Strongest on Record
http://www.space.com/scienceastronomy/x ... 31105.html

Quote:
The strongest flares on record, in 1989 and 2001, were rated at X20. This one is at least that powerful, scientists say. But because it saturated the X-ray detector aboard NOAA's GOES satellite that monitors the Sun, a full analysis has not been done.

The satellite was blinded for 11 minutes.

Craig DeForest, a solar physicist at the Southwest Research Institute, said others in his field are discussing the possibility that Tuesday's flare was an X40.

"I'd take a stand and say it appears to be about X40 based on extrapolation of the X-ray flux into the saturated period," DeForest told SPACE.com.

Mayb need to check recent flares.

Gallery of solar flares

http://www.space.com/php/multimedia/ima ... 62&gid=243
SPACE.com Image Gallery: HOT STUFF: Solar Flares

[harry]

G'day from the land of ozzzzzz


Re above link

Hubble did not agree with the expansion idea and thought that the redshift was an "hitherto unknown principle of nature". The redshift is due to the conservation of energy:E= - mGM/r + mcv giving in the Continuity Equation :


GM/r^2 = cDel.v = (cv/r)cos(p) giving cos(p) = v/c = z.

Hubble's Constant is H=Del.v = (v/r)cos(p) = fcos(p).

There is further confusion about the redshift, the centrifugal force cDel.v causes center-fleeing behavior not center-seeking behavior. The deflection is away from the gravity center not towards the gravity center. This redshift is the "source" of the "dark energy" , moving masses.

This link maybe of interest

http://arxiv.org/abs/0903.3121
Incorporating Photometric Redshift Probability Density Information into Real-Space Clustering Measurements

Authors: Adam D Myers (1), Martin White (2), Nicholas M. Ball (1) ((1) UIUC (2) Berkeley)
(Submitted on 18 Mar 2009)

Abstract: The use of photometric redshifts in cosmology is increasing. Often, however these photo-zs are treated like spectroscopic observations, in that the peak of the photometric redshift, rather than the full probability density function (PDF), is used. This overlooks useful information inherent in the full PDF. We introduce a new real-space estimator for one of the most used cosmological statistics, the 2-point correlation function, that weights by the PDF of individual photometric objects in a manner that is optimal when Poisson statistics dominate. As our estimator does not bin based on the PDF peak it substantially enhances the clustering signal by usefully incorporating information from all photometric objects that overlap the redshift bin of interest. As a real-world application, we measure QSO clustering in the Sloan Digital Sky Survey (SDSS) and find that our estimator improves the clustering signal by a factor equivalent to increasing the survey size by a factor of 2 to 3. Our technique uses spectroscopic data to anchor the distance scale and it will be particularly useful where spectroscopic data (e.g, from BOSS) overlaps deeper photometry (e.g., from Pan-STARRS, DES or the LSST). We additionally provide simple, informative expressions to determine when our estimator will be competitive with the autocorrelation of spectroscopic objects. Although we use QSOs as an example population, our estimator can and should be applied to any clustering estimate that uses photometric objects.

and

http://arxiv.org/abs/0902.0429
The Coyote Universe II: Cosmological Models and Precision Emulation of the Nonlinear Matter Power Spectrum

Authors: Katrin Heitmann, David Higdon, Martin White, Salman Habib, Brian J. Williams, Christian Wagner
(Submitted on 3 Feb 2009)

Abstract: The power spectrum of density fluctuations is a foundational source of cosmological information. Precision cosmological probes targeted primarily at investigations of dark energy require accurate theoretical determinations of the power spectrum in the nonlinear regime. To exploit the observational power of future cosmological surveys, accuracy demands on the theory are at the one percent level or better. Numerical simulations are currently the only way to produce sufficiently error-controlled predictions for the power spectrum. The very high computational cost of (precision) N-body simulations is a major obstacle to obtaining predictions in the nonlinear regime, while scanning over cosmological parameters. Near-future observations, however, are likely to provide a meaningful constraint only on constant dark energy equation of state 'wCDM' cosmologies. In this paper we demonstrate that a limited set of only 37 cosmological models -- the "Coyote Universe" suite -- can be used to predict the nonlinear matter power spectrum at the required accuracy over a prior parameter range set by cosmic microwave background observations. This paper is the second in a series of three, with the final aim to provide a high-accuracy prediction scheme for the nonlinear matter power spectrum for wCDM cosmologies.

[aristarchusinexile]

My parents told me that when I was two years old I thought Scotch tape could repair anything. Kinda similar sophistication in thought, only I grew up a little since then.

Obviously your culture is not as sophisticated as ours in Canada, Apeman, or at two years of age you would have known Duct Tape fixes anything, not Scotch Tape. Your culture can be forgiven, though, as Red Green is, after all, a Canadian.

P.S. I sure wish I knew what the heck Harry is talking about in the posts above. Is it leaning towards Redshift perhaps not being caused by expansion?

[aristarchusinexile]

G'dafrom the land of ozzzzz

This paper goes back to 2003

Still quite interesting.

Latest Sun Flare Put at X28, Strongest on Record

If Dark Matter exists, could these large flares affect its temperature?

[harry]

G'day Chris

Dark matter and dark energy, you need to know what type and where.

Dark matter and dark energy as refered to by the BBT in my opinion is an ad hoc idea to make the theory work.

Dark matter and dark energy that is found as an unknown in compact objects is another issue that can be treated by the laws of physics and our undertsanding of quantum mechanics.

So on one hand you have dark matter/energy as per the BBT doing their thing and on the other hand dark matter/energy creating the moment.

This maybe of interest to you, its not a selective link,,,,,,,smile

Dark Matter astrophysics 2009

http://arxiv.org/find/all/1/all:+AND+20 ... /0/all/0/1

just a random link

http://arxiv.org/abs/0711.0470
Free streaming in mixed dark matter

Authors: Daniel Boyanovsky
(Submitted on 3 Nov 2007 (v1), last revised 14 Dec 2007 (this version, v2))

Abstract: Free streaming in a \emph{mixture} of collisionless non-relativistic dark matter (DM) particles is studied by implementing methods from the theory of multicomponent plasmas. The mixture includes Fermionic, condensed and non condensed Bosonic particles decoupling in equilibrium while relativistic, heavy non-relativistic thermal relics (WIMPs), and sterile neutrinos that decouple \emph{out of equilibrium} when they are relativistic. The free-streaming length $\lambda_{fs}$ is obtained from the marginal zero of the gravitational polarization function, which separates short wavelength Landau-damped from long wavelength Jeans-unstable \emph{collective} modes. At redshift $z$ we find $ \frac{1}{\lambda^2_{fs}(z)}= \frac{1}{(1+z)} \big[\frac{0.071}{\textrm{kpc}} \big]^2 \sum_{a}\nu_a g^{2/3}_{d,a}({m_a}/{\mathrm{keV}})^2 I_a $,where $0\leq \nu_a \leq 1$ are the \emph{fractions} of the respective DM components of mass $m_a$ that decouple when the effective number of ultrarelativistic degrees of freedom is $g_{d,a}$, and $I_a$ only depend on the distribution functions at decoupling, given explicitly in all cases. If sterile neutrinos produced either resonantly or non-resonantly that decouple near the QCD scale are the \emph{only} DM component,we find $\lambda_{fs}(0) \simeq 7 \mathrm{kpc} (\mathrm{keV}/m)$ (non-resonant), $\lambda_{fs}(0) \simeq 1.73 \mathrm{kpc} (\mathrm{keV}/m)$ (resonant).If WIMPs with $m_{wimp} \gtrsim 100 \mathrm{GeV}$ decoupling at $T_d \gtrsim 10 \mathrm{MeV}$ are present in the mixture with $\nu_{wimp} \gg 10^{-12}$,$\lambda_{fs}(0) \lesssim 6.5 \times 10^{-3} \mathrm{pc}$ is \emph{dominated} by CDM. If a Bose Einstein condensate is a DM component its free streaming length is consistent with CDM because of the infrared enhancement of the distribution function.

To understand cosmology you need to read and most what you read maybe crap, thats the 80/20 principle.

[Qev]

G'day from the land of ozzzzzz

Apply the black box approach.

What ever happens within the Gyr box cannnot effect time outside.

You cannot alter time in one area and not effect time in another.

You cannot alter your measurement of the passage of time in your own frame of reference, period; the idea doesn't even make sense without a comparison to another frame. Relative motion will cause you to measure the time passing in other frames of reference differently, though.

[JimJast]

Hubble did not agree with the expansion idea and thought that the redshift was an "hitherto unknown principle of nature".

The "unknown principle" turned out in 1985 to be the old principle of conservation of energy. It turned out that Einstein's original general relativity requires, because of this principle, that there is a drop of proper time rate per unit of distance from the observer, equal to the curvature of space (which makes the "accelerating expansion of space" an illusion). But the cosmologists already updated general relativity with the assumption of real accelerating expansion of space which would have to be rejected if Einstein's original general relativity were to be reinstated. Einstein was already dead for 30 years and there were lots of living cosmologists trying to make careers in cosmology, so the editors of scientific journals decided to delay publishing the news about the predictive power of Einstein's general relativity. Even when it turned out in 1998 that the value of acceleration of this apparent expansion is exactly as Einstein's original general relativity predicted.

Isn't also your opinion that the careers of living people are more important to predictions of old theories. Especially in astronomy, which "unlike in civil engineering, one may be 100% wrong and nobody is hurt" (as my astronomy teacher from Harvard, Alan Lautman, kept saying).

[harry]

G'day Qev

Qev said

You cannot alter your measurement of the passage of time in your own frame of reference, period; the idea doesn't even make sense without a comparison to another frame. Relative motion will cause you to measure the time passing in other frames of reference differently, though.

Yep yep yep,,,,,,,,,I agree

[aristarchusinexile]

There is certainly no doubt that light travels slower than c in any medium.

In the past month I read of light being sped 300 times beyond c in (cessium gas?)

[aristarchusinexile]

Ah come on .. someone say something about this.

[aristarchusinexile]

"...careers of living people are more important to predictions of old theories. Especially in astronomy, which "unlike in civil engineering, one may be 100% wrong and nobody is hurt" (as my astronomy teacher from Harvard, Alan Lautman, kept saying).

I agree except, unfortunately, that Civil Engineers must be held accountable for their lack of discipline also, especially because it

does

cause deaths.

[JimJast]

In the past month I read of light being sped 300 times beyond c in (cessium gas?)

It is not the speed of light but only the phase speed of light. Some people keep dropping adjectives. Then non physicists who read this stuff get confused.

The phase speed can be anything since it is only the speed of the picture of the wave. It is like setting a line of people and tell each of them to raise his hand and certain predefined time. The observer may see a "wave of hands" moving along the line with certain speed. This speed may be greater than speed of light, since it can be anything. It has no physical connection to any physical speed. It is only an image of a "wave of hands" in the eye of observer. Similar effect with "speed of waves" on water. The waves "move" while water stays, just oscilates a little bit making an impression of fast or slow waves.

[aristarchusinexile]

In the past month I read of light being sped 300 times beyond c in (cessium gas?)

It is not the speed of light but only the phase speed of light. Some people keep dropping adjectives. Then non physicists who read this stuff get confused.

The phase speed can be anything since it is only the speed of the picture of the wave. It is like setting a line of people and tell each of them to raise his hand and certain predefined time. The observer may see a "wave of hands" moving along the line with certain speed. This speed may be greater than speed of light, since it can be anything. It has no physical connection to any physical speed. It is only an image of a "wave of hands" in the eye of observer. Similar effect with "speed of waves" on water. The waves "move" while water stays, just oscilates a little bit making an impression of fast or slow waves.

With light it is the wave that is the light .. with water the wave is in the water.

[Chris Peterson]

With light it is the wave that is the light .. with water the wave is in the water.

Actually, when evaluating speed of light claims, it is best to avoid the wave model completely, and simply consider the energy carriers, photons. The question becomes whether you can transmit a photon faster than c, or restated, whether you can transmit information faster than c.

Light is not a wave, at least not in a way analogous to water waves. A "light wave" isn't in anything, nor is the light itself a wave. Light consists of particles, and QM describes the way that all particles, not just light, can exhibit wave-like behavior.

[JimJast]

"Most of us live in urban worlds where we think everything's totally well known," Beehler said. "It's a little bit of a reminder, just a wake up call, that we really need to know our world better so we can manage it better."

But talking about knowing our world better and about astronomy, it might be remided that those sophisticated cosmologists have ruled out "Einstein's universe" since they enhanced general relativity, against Einstein's better judgement, with the axiom of expanding space. This axiom is supported only with another axiom saying that cosmological redshift is surely Doppler shift and not somethng that follows from Einstein's gravitation (which it is and it could be easily demonstrated if it were legal in this forum).

[JimJast]

Light is not a wave [...]

And yet phase velocity (the one greater than c) refers to the phase of wave. Only the phase can move with speed greater than c since it is not a physical speed and it is only the "speed of an image in human brain" and this one can "move" at any speed. It is also the "apparent speed" of wave front. While this is true that light is not a wave, most people keep talking about "water waves", "radio waves", etc. since they can imagine them this way. Like they can imagine that the universe is expanding, despite it is not possible physically (because Einstein's general relativity necessarily complies with the principle of conservation of energy and Hubble redshift solely due to expansion would violate this principle).

[aristarchusinexile]

With light it is the wave that is the light .. with water the wave is in the water.

Actually, when evaluating speed of light claims, it is best to avoid the wave model completely, and simply consider the energy carriers, photons. The question becomes whether you can transmit a photon faster than c, or restated, whether you can transmit information faster than c.

Light is not a wave, at least not in a way analogous to water waves. A "light wave" isn't in anything, nor is the light itself a wave. Light consists of particles, and QM describes the way that all particles, not just light, can exhibit wave-like behavior.

My point exactly.

[harry]

G'day from te land of ozzzzzz

Very Long Baseline Array Reveals Formation Region of Giant Cosmic Jet Near a Black Hole
http://hubblesite.org/newscenter/archiv ... s/1999/43/

1. What causes the beams?


Material at the center of M87 is drawn inward by the black hole's strong gravitational grip. This material forms a rapidly spinning flat disk, called an accretion disk. Astronomers believe that some material escapes along the poles of this disk, forming a wide jet. Magnetic fields in the disk may pinch the jet into narrow beams. Black holes are compact, dense powerhouses at the core of galaxies.

2. What does this finding mean?


Astronomers always had speculated that the jet had to be made by some mechanism relatively near the black hole, but as they looked closer to the center, they kept seeing an already-formed beam. Now astronomers have shown that M87's jet is formed within a few tenths of a light-year of the galaxy's core, presumed to be a black hole three billion times more massive than the Sun. This new information will help scientists decipher how these powerful "engines" work.

[Qev]

G'day Qev

Qev said

You cannot alter your measurement of the passage of time in your own frame of reference, period; the idea doesn't even make sense without a comparison to another frame. Relative motion will cause you to measure the time passing in other frames of reference differently, though.

Yep yep yep,,,,,,,,,I agree

So, to be clear, you're agreeing that every observer experiences their own unique flow of time, and that there is no such thing as 'Actual Time'?

[harry]

G'day Qev

OK I agree.

Now what are you gettting at?

Time cannot be changed.

[harry]

G'day from the land of ozzzzz

I posted this in another folder.

I should have posted here.

Mark swain said

How compacted does matter/energy have to be, before gravity reverses to the point where the total mass can no longer with stand the internal reverse? And if this was the reason for the bb would this not explain why some matter is still in a reverse gravity state and still pushing outwards?

I do not think Its a matter of how much density matter is, its the magnetic reconnection ratio with the central core mass and the infalling matter. To create a vortex that can escape a so called black hole whether it starts from the core or around the core it requires a magnetic field that can keep it stable. The stronger the magnetic field the greater is the stability and some of these jets can go for millions of light years and some like the ones on the surface of the sun will fizz off very quickly.

Sun Jet movies
http://science.nasa.gov/headlines/y2007 ... ayjets.htm

Galaxy jets
http://chandra.harvard.edu/press/00_rel ... 00pic.html

http://chandra.harvard.edu/press/08_rel ... 11008.html


http://chandra.harvard.edu/photo/2006/3c273/

'Death Star' Galaxy Black Hole Fires at Neighboring Galaxy
http://chandra.harvard.edu/press/07_rel ... 21707.html

"We've seen many jets produced by black holes, but this is the first time we've seen one punch into another galaxy like we're seeing here," said Dan Evans, a scientist at the Harvard-Smithsonian Center for Astrophysics and leader of the study. "This jet could be causing all sorts of problems for the smaller galaxy it is pummeling."

and so on.

Magnetic reconnection is the Key Process.