Martin

No sneer intended. It was a reasonable question.

...

No, not a reasonable question. You should retract the question.

I did not assert or assume finiteness. You pretended that I did and asked me to justify something I had not claimed. You asked if I was presuming finiteness merely because it "sounded good".

I am offended by your misrepresentation and by the sarcastic suggestion that I would presume something without evidence because it sounded good (whatever that means).

You should retract the insulting question (which contains a misrepresentation) and apologize for having given offense.

Unless you are just trolling, you seem to suffer from a lack of information. If you want people to share facts with you, you have got to deal honestly and politely with them. If you do not, you will just be shooting yourself in the foot.

This may sound harsh but it is kindly meant.

This is what you need to start by retracting:

Ok. Thanks. So should I assume that isotropy does not imply 'finite' either? If so, then how have you, or anyone else arrived at the presumption that it IS finite? Where is your actual evidence? The math? The obsevations? Or do you presume it because it sounds good to you?

Ok. Thanks. So should I assume that isotropy does not imply 'finite' either? If so, then how have you, or anyone else arrived at the presumption that it IS finite? Where is your actual evidence? The math? The obsevations? Or do you presume it because it sounds good to you?

...

Another error: the Straw Man ploy.

I have not claimed that space is finite. I do not assume that it is. I've said we don't know finite or infinite.

You impute that "presumption" and challenge me to offer evidence.

Then you sneer. "Do you presume it because it sounds good to you."

But I have not presumed anything. **TILT**

Lots of errors, too many to address the whole batch. Here's a logic error.

homog. and iso. do not imply space is infinite

Logic says they imply one of 3 things. Infinity. Finite. Or Nothing. ...

Thank you. Feel free to reign me in when I get out of line ...

Consider yourself reigned in. Here we are talking simple logic. Not science. Not physics. Not astronomy.

I point out that A does not imply B.

You say "logic says" that therefore A must imply something else, like maybe not-B. That is an elementary non-sequitur.

Py I simply do not have time to correct all your mistakes. I will get back to this as time permits and point out a few more.

Py,

I'm shortening your name for friendlies. If you don't like Wakit you can be Py. No disrespect at all!

If you don't like Py, tell me. I think it's a nice familiar nickname but maybe it doesn't fit you.

Astro/Cosmo is for conventional scientific consensus Astro/Cosmo.

It is not for "against the standard model" or for Personal Theories.

Personal or Individual theories go in Speculation Forum

Part of our job is educational about standard science, so we sort things out from time to time to keep a modicum of order. If you want to explore a variant, show that you understand the standard model first.

'Wakit you have a lot of mistakes here. You sound so sure of yourself that no one is likely to want to try to correct you.

In cosmology we don't assume that the universe is exactly homogenous and isotropic. That is assumed to be true only as a largescale approximation.

Moreover it is not an assumption about empty space devoid of matter. It is an assumption about distribution of matter.

The distribution of matter is assumed to be co-extensive with space and to be approximately uniform (homog. and iso.) in the largescale average.

That's one mistake.

Another mistaken idea you have is that homog. and iso. imply infinite.

There are many cosmo models which satisfy the uniformity principle which have space be a finite volume, with a finite circumference. They have been studied for years and are well-known. That case has not been ruled out and NASA published an estimated lower bound on the size just this year.

As I recall it amounted to a circumference of about 600 billion light years.

That was a blue-ribbon NASA report from the WMAP mission.

So it is ridiculous to claim that uniform implies space infinite. It is not rational. Counterexamples abound!

If you don't already understand this, then you need to be asking questions at this forum, not making statements.

Sounds like DeGrasse-Tyson was trying to explain, but couldn't take the time to hammer it in. He probably had to oversimplify and leave out part of the message, but he gave you the important part. We don't know whether space has finite volume or infinite volume. We assume matter is coextensive with space, distributed approx uniformly (the structure looks cob-webby at smaller scale and clustery at even smaller, galactic, scale).

As new data comes in, it is analyze and the results are tabulated using both the finite and infinite models because we don't know yet.

But we are getting closer to knowing, so stay tuned.

Merged post follows:

I vote that we create a stickied thread about the space ending vs. not ending debate. The first post should be detailed giving a basic reading to a more advanced reading.

Space having a finite volume does not imply that space "ends" anywhere or that space has a boundary.

In cosmology we normally assume that space does not have a boundary.

It's simpler that way. Einstein's model(s) of the universe did not have a boundary, and all their descendent models worked out by other people so nor have boundaries.

And typically matter is approximately uniform and coextensive with space, so if space has finite volume there is a finite amount of matter.

And if space has infinite volume there must be an infinite amount of matter.

In either case (finite or infinite) there is no border of any sort, no "end", no boundary, to space-and-matter.

I'm not talking about singularities, where in some models if you go back far enough in time the model might terminate. That's a separate issue, although it terminates spacetime it's not a boundary to space in the sense we're talking about. Nor is in other cases if you go far enough into the future and get a crunch singularity.

Cosmologists are developing models that don't have those breakdown points---don't have singularities---so that kind of terminus is gotten rid of as well, but that's a different issue.

I don't know if your idea of sticky thread is good. It is not a debate for amateur philosophers though. It is a place where if you don't understand conventional standard cosmology you should start asking questions.

Whether or not a sticky is good, I don't know. What experience has shown, though, is that people who come into a discussion like this should start by asking questions until they understand the ordinary professional working astronomers' picture.

...Certainly, the space between galaxy clusters, called the voids, is nearly empty...

Surrounding and stretching between galaxies, there is a rarefied plasma[24][25] that is thought to possess a cosmic filamentary structure[26] and that is slightly denser than the [edit: voids]. This material is called the intergalactic medium (IGM) and is mostly ionized hydrogen, i.e. a plasma consisting of equal numbers of electrons and protons. The IGM is thought to exist at a density of 10 to 100 times the average density of the [edit: voids].

... As gas falls into the Intergalactic Medium from the voids, it heats up to temperatures of 10^5 K to 10^7 K,...

I don't think there is a discrepancy, more like an ambiguity in wording. I edited to make it clear that the IGM filamentary structure has a higher density than the voids.

Filamentary structure means the cobwebby structure that you may have seen pictures of. If you haven't, then google

"Smoot TED"

for a wonderful 15 minute talk about the filamentary structure and how it formed. There are computer animations that show it forming.

The cobwebs include clusters of galaxies and stretch between neighboring clusters. The structure can actually be observed.

Things started out more evenly distributed but whereever there was a slight overdensity that would cause surrounding matter to fall towards it.

So you get huge structures of overdensity stretching thru regions of underdensity (relative voids) and the stuff in the comparative voids is always falling like hail down into the comparative condensed cobwebby structures.

So it heats up by falling, gains speed, particles collide. Atoms ionize due to collisions.

The filaments are still quite un-dense by our standards:D. But they are significantly denser than the voids.

At scattered points in those filaments, especially where two filaments cross, you get more condensation. Clusters of galaxies begin to form at crossing points and at other scattered points.

We still aren't down to the level of individual galaxies like the Milky Way or like Andromeda. Individual galaxies tend to form in groups, various size clusters. So the key thing we are looking at are the clusters (which people map, and then they see the filamentary structure sort of outlined by the clusters of galaxies.)

TED is an organization that puts on lectures. George Smoot is a nobel cosmologist. If you google "Smoot TED" you will get this:

It's online video of a great talk. I think anybody interested in the structure of the universe should check it out.

Louis Crane is a math professor at Kansas State who has published a bunch of legitimate mathematical physics research in the usual peer-review journals. He also produces research papers that don't get published, for whatever reason:

http://www.slac.stanford.edu/spires/find/hep/www?rawcmd=a+Crane%2C+Louis&FORMAT=WWW&SEQUENCE=

Three years ago, Crane applied for and was awarded a $2 million grant from a foundation called FQXi which has the stated aim of supporting far-out research that would not normally be funded by the government.

His proposal was to study the feasibility of using black holes to power spaceships.

Crane did, indeed, deliver the goods. He duly performed the proposed study as he had promised FQXi he would. The result appeared in August 2009.

http://arXiv.org/abs/0908.1803

Are Black Hole Starships Possible?

Louis Crane, Shawn Westmoreland

20 pages

(Submitted on 12 Aug 2009)

"We investigate whether it is physically possible to build starships or power sources using the Hawking radiation of an artificial black hole as a power source. The proposal seems to be at the edge of possibility, but quantum gravity effects could change the picture."

Some people might be interested in checking this out. In order to be useful, the black holes need to be quite small---on the order of 1/10 of a nanometer--comparable in size to atoms--or smaller. He calls them "subatomic black holes" or SBH.

Such small black holes radiate intensely. (Hawking radiation temperature varies inversely with the size of the BH).

They need to be fed, because if they are allowed to evaporate and shrink down to much less than ideal size the radiation becomes too intense and they effectively explode. You want them small, but not too small. So as they radiate away mass you should keep feeding them.

The work is based on the same standard BH physics, the same formulas, that are used in doing normal astrophysical BH calculations. He just plugs in different size and mass numbers---instead of stellar masses, much smaller masses on the order of a few hundred thousand tons.

I considered putting this in Speculation, but it has considerable amount of kosher physics, and is by an established author, so decided it was borderline legit.

Crane also submitted a brief non-technical essay on this idea to a FQXi essay contest:

http://fqxi.org/community/forum/topic/525

He got his PhD from Chicago in 1985, postdoc'd at Princeton Institute for

Advanced Study, was Assistant Professor at Yale for a while, then took the tenured faculty position at Kansas State.

http://www.math.columbia.edu/~woit/wordpress/?p=2542

"A few minutes ago, one of the beams of the LHC was ramped up to an energy of 1180 GeV, besting the Tevatron’s top beam energy of 980 GeV.

Update: Actually the beam was lost at 1070 GeV, which is still a record high energy."

==========================

An update says that they now have gotten each beam up to 1180 GeV. It also gives a figure for the brightness (how many particles fly past per second).

So with two beams each at 1.2 TeV they could be looking at collisions with a total energy of 2.4 TeV. Already this is somewhat higher than what has been produced at the older Fermilab collider---the socalled "Tevatron".

A fan of the LHC put together this excellent LHC portal, the announcement is in "news" forum. Its a volunteer effort--all this stuff is gathered and organized to make it accessible. I really like what he's done.

Two things. There is a timelapse montage of webcam footage showing the assembly of the ATLAS detector compressed into 5 minutes. Real people and events, but flashing past extremely quickly and the whole thing gradually coalesces.

But what is more educational is to first watch a couple of 6 or 7 minute computer animation tutorials, that peel off the ATLAS layers and say what each does. So how the various particles can be distinguished and tracked and their energies measured.

You may have already seen these tutorial animations---they are extremely good. Once you watch them, then when you look at the 5 minute timelapse of the actual realworld assembly of ATLAS you can recognize the various components and layers as they are fitted on.

This LHC "fan-site" has not so far been commercialized.

http://www.LHCPortal.com/

It does not have advertisements cluttering it up. It would be beautiful if it stays that way---a pure labor of love by whoever the guy is.

I would say enjoy it now before it gets popular and runs the risk of getting advertisements. Or shut down by the CERN management because as a volunteer effort it is not an official part of their public relations.

If you go to LHCPortal.com you get links to all the goodies, but here's a sample on Youtube of the kind of thing Portal links you to.

These are animations which have been available for a couple of years. They are not the actual webcam montage, which only became available a month or so ago. I don't have the link for that handy. The title is something like "Atlas built in 5 minutes".

If you find any stuff on Portal you think might be interesting please post a link to it.

Ah! I found a Youtube link that has that "Atlas built in 5 minutes" thing on its menu:

http://www.youtube.com/TheATLASExperiment

I just checked out the new site.

Has some fascinating "fly on the wall" stuff. You can spend a lot of time poking around. Webcams at various locations. Screens from actual monitors, reporting up-to-the-minute status of this or that system.

It also has a collection of goodies that the CERN public outreach people have prepared----like animation/photography showing the construction/planned operation of ATLAS compressed into a few minutes.

http://www.LHCPortal.com/

It is an independent volunteer effort, I would reckon.

The guy might conceivably eventually get some income from advertising if the site gets very popular. But it looks like no one is paying him. All the stuff is freely available, but he is doing the work of gathering it all together and organizing it so you can easily navigate around.

Looking good. I wish him success, whoever the guy is.

I would guess it is an under-thirty techno-freak

This is, in my respectful opinion, beautifully presented. The language is evocative. Nice use of familiar images and everyday language.

What you have here is a fantasy that borders on poetry.

I think this should be encouraged and appreciated, if it is well presented, but should also be distinguished from science.

Science is empirical. Every idea should be testable by experiment or by observation. This was proposed by Francis Bacon. He was a contemporary of Shakespeare. We've had this tradition of Empiricism for 400 years now, sometimes referred to as the Baconian tradition. It's under attack. Some people want to give up on testability and go back to an earlier type of pre-Baconian "science" that was more along the lines of explanatory fantasy---a kind of philosophical myth-making without an experimental way to show if it's wrong.

About all we can do here is maintain a clear distinction.

So I moved this out of Physics and into Speculations forum.

=================

There is at least one "tree of universes" concept which purports to be testable. You can read about it in the book by Lee Smolin called "The Life of the Cosmos".

What I mean by "tree of universes" is the kind of model where black holes sprout off to make new universes and those universes make more black holes, which in turn sprout further generations of universes. It is a kind of branching picture or "family tree" of existence. His version of the idea allows for small variations at each branch-point----each offspring universe can have slightly different values of the basic constants (the ratio of electric force to gravitational force can be slightly different, or the ratio of masses of basic particles can be slightly different)---the offspring tract of spacetime can be slightly different from the parent tract.

In broad outline, Smolin's idea is similar to yours. But he included some mathematical content and thought of a way to test it observationally.

The book has been out for about 10 years now. They might have it at your local public library. The idea has been discussed in other books since then. A chapter devoted to it here and there. Also articles about it in the professional physics journals. It has been attacked, and the attacks have been rebutted. The usual stuff that happens in science. Empirical tests have so far not invalidated the idea---it survives.

The important distinction, if I can repeat, is that Smolin's version of the idea comes equipped with some quantitative mathematics and several ways to test it (such as measuring the masses of neutron stars, which can be and is being done.) Without that testability feature, the idea would just be a myth, appealing to the imagination.

http://www.boston.com/bigpicture/2009/11/martian_landscapes.html?amazing

All these Mars landscape shots are incredible and astonishingly beautiful. Some are taken from over the polar icecaps

Apologies if somebody already posted link to these.

I'm interested in robotics, AI, the human mind, etc. I want to do something meaningful to push the human race to its peak. There will definitely be some radical changes in our life-time, and I want to be on board. This is why I dropped out of chemical engineering, it didn't seem tailor[ed] to what I wanted to get involved with.

 

Any input would be appreciated. I've come to you guys because I'm not sure if any advis[o]rs would take me seriously.

That all makes sense, at least to me. To get any good out of a board like this it is important for you to talk. Talk about your motivation, your passion, and whatever is problematic in your situation---see where it leads you.

Our advice, at least mine (to speak for myself) cannot be all that specific or reliable because we can't assess you and your situation directly.

Is ECE the right major? I was thinking about cognitive science, computer science, or even biology, but I believe that ECE seems to works the best in this case.

In the evolutionary landscape there are many peaks---not just one. It is good to want to help push the human race up whatever slope. Don't get hypnotized by the ideology (or rhetorical style) of one particular vision of THE peak.

ALL the majors you mentioned can lead to careers that make a significant contribution to getting up some slope. For example maintaining a breathable atmosphere and extracting minerals in an off-earth environment are largely Chem Eng problems. Biofuel and microbial protein production are likely to be critical Chem Eng technologies on earth as well as off.

And of course you listed some other smart picks on your menu---like robotics, like cognitive, like computer science.

The people that get into exciting careers and make a contribution to pushing the human race up some of the many slopes we are climbing will probably be ones who focused on whatever undergrad major and did well in whatever major, and then went on and got a masters in something else.

There is no one strategic optimal major---there are half a dozen majors you could pick. The important thing is to pick one that you can do well in, and get intensely interested in---here and now.

Ideally a major should be something where you can get intense satisfaction out of mastering the current state of the art (and being better than the other students) right here and now. It is by being good at the undergrad level that you get the best options for your masters. Or for hires where you can learn stuff on the job.

I'm currently a freshman in college and I'm trying to pick a major to stay with. I decided to come to the university with a major in chemical engineering, but I'm not interested in the current material (mainly chemistry), nor what is to come (thermo, fluid, etc etc..).

 

At this point I'm thinking of switching to electrical/computer engineering. My problem is that I don't have a lot of knowledge in the area.

Your saying ECE sounds like you visualize working in robotics. And your comment about chem, thermo, fluid suggests to me that you like to visualize definite objects rather than continuous media like liquids and gasses.

Did you also think about mechanical engineering? Oh wait, probably you did not do a lot of shop, building actual stuff. You sound more like a desk thinker and less like a nuts-bolts machine-shop guy.

ECE actually sounds like a good major, assuming you really get into it and can excel in one or more of the specialties that comprise it.

Why wouldn't some young idealistic faculty in the ECE department be good for you to talk to? You don't need to sign up for an official advisor. You can go over to the building---walk down the hall, read who does what, see who is having office hours, and drop in on somebody who is having open office hours. I would talk to some young faculty, not some old fart. And someone who is involved with a branch of ECE that you think is potentially inspiring---that you can talk to them about.

Not all advisors are equal. I would say make some informal contacts and find someone to talk to whose passions and motivation have some connection with your own---do that first and as soon as you can, before signing up for an official advisor.

Why shouldn't some ECE faculty take you seriously?

WHOAH!!!! I JUST SAW YOUR POST #3! This makes my response here seem to be the wrong one!

My problem is that I don't have a passion, or something I truly love. I have general interests, but that's about it.

At least you have some abstract intellectual passions like Jack Kurzweil---you like to imagine the future and talk about it. You like to read futurology books. Can you write? Maybe you have a passion for communication. Have you ever given a talk in front of a group, or led discussion? Would you like to have a successful blog about something? Have you considered having a blog? Or tried it. What have you wanted to do enough so that you have failed at it once already?

Come on. Don't say you completely lack passion. BTW do you know the Greek derivation of the word Arkturus? An arkt-ouros is a professional of a certain type. It is a respectable, although slightly dangerous, job category. Arktouroi train bears to dance and do tricks. Like getting bears to wear hats and walk on their hind-legs. Maybe this is an omen---perhaps your destiny is to become a highschool science teacher!

(There is no profession I know of that helps more to push humanity up the slopes than the teacher profession, whether college or highschool---or which fails more at its job.)

So talk, Arktouros. Only by writing posts will you get any good out of this board. The only advice that is good is what comes from the inside.

...The value 2.8615 was derived using the solar mass but, if the sun were to collapse into a Black Hole it would of course, include the mass of the planets. ...

Why would it necessarily include the mass of the planets?

I have another question as well, elas. What value are you using for the mass of the sun? Is it in kilograms? How many kilograms? Different books can differ in the numbers they give (it will depend on the value of Newton's constant which the author of the book is using.)

i didn't read the pdf, but from the abstract "Our universe might be understood in terms of vast computer simulations and could even have been created and transcended by one "

isn't he just ripping off the hitchhikers guide to the galaxy?

What you quote is far from being the main point of the article. I guess I'm feeling especially grouchy about this. Read the full article, or not, as you please.

Merged post follows:

i didn't read the pdf, but from the abstract "Our universe might be understood in terms of vast computer simulations and could even have been created and transcended by one "

isn't he just ripping off the hitchhikers guide to the galaxy?

Moth, thanks for taking the article seriously enough to read it (as by now I'm sure you have). I think this article by R. Vaas is just one of several signs that are pointing to a trend----one that I find disturbing, but that is just my private reaction and of no particular consequence.

I should just shut up about my own chagrin at this paper and try to discuss it objectively.

You are quite right about the connection with Douglas Adams' satire. Adams is wonderfully funny. The trouble with Vaas is he is encouraging readers to consider as sober possibility what has been around for some time in the form of science humor and fantasy.

What stands out for me (which he does not label as such) I would call "secular creationism."

BTW your mentioning Douglas Adams reminds me that another fiction writer, Kurt Vonnegut, had some fun with secular creationist fantasies. The title that comes to mind is "The Sirens of Titan", but this goes 40 years back and my memory of it is quite vague. Dark humor. Comic paranoia.

Maybe the best way to deal with Vaas is to laugh at him!

In my humble estimation Rudy Vaas has gone off the deep end in a very serious way:

http://arxiv.org/abs/0910.5579

And I think he is a force to be reckoned with because he is an editor of a German equivalent of Scientific American called "Bild der Wissenschaft". He has academic credentials as well (university faculty, Philosophy of Science, at Giessen)

and he writes and edits books, that get published.

So I think international public attention will be paid to his ideas, which have become very speculative---and gone way beyond what can honestly be said to be empirical testable science.

Unless I'm mistaken, he is no longer doing professional Philosophy of Science but is peddling a kind of "mind candy" which appeals to the imagination.

My feeling is that this is out of the bag. It is out, whether I post about it or not. So we might as well get used to it. Other people who don't have quite as much in the way of credentials or communication skills may have already broached this. Maybe there will be an "immune response".

I'm disappointed in Rudy because in the past he has written articles which I thought were intelligent and helpful---both academic papers and illustrated magazine popularizations.

He's talking about some kind of secular intelligent design.

Abstract of a paper delivered this month

http://gsa.confex.com/gsa/2009AM/finalprogram/abstract_160197.htm

Much larger event than Chicxulub, where the bolide is thought to have been only 8-10 km in diameter.

Physorg.com has this commentary:

http://www.physorg.com/news174827113.html

Apparently 3 things happened about the same time as the dino extinction some 65 million years ago:

1. Chicxulub---an estim 8-10 km bolide hits Earth off the coast of Yucatan in Gulf of Mexico.

2. Shiva---an estim 40 km bolide hits west of India off coast of Mumbai. Actually breaks off a chip of the tectonic plate, making a separate little Seychelle plate that drifts over towards Africa.

3. Series of massive volcanic eruptions forming the socalled Deccan Traps in India.

Maybe someone would like to give more detail on this? I don't know in what order these events occurred, or what the dates attributed to them signify. I've heard other theories about dino extinction.

You mean Gravitational time dilation. What does GPS have to do with gravitational redshift?

Everything. The GPS satellites are up higher than we are. They carry atomic clocks. These atomic clocks run faster than clocks on the surface of the planet, which are deeper down in the gravitational potential well.

Being deeper in gravitational potential slows clocks and also the vibrations of lightwaves by the same factor. That is called gravitational redshift.

Does it happen to Jupiter? and has anyone measured it?

I think Swansont already told you yes and yes. There was a measurement involving Jupiter gravity and (indirectly) time. I'm not at all clear about the details.

Maybe you could take the name Swansont gave you, and look up his papers, and see if there was something. Try to find something on your own before asking again.

Just go to arxiv.org, select "search" and type in the author's name.

http://arxiv.org/

*selects search and gets* http://arxiv.org/multi?group=grp_physics&%2Ffind=Search

*types Kopeikin and gets* http://arxiv.org/find/grp_physics/1/au:+Kopeikin/0/1/0/all/0/1

Ooops, I got curious myself and did a search for Kopeikin and found this 2003 paper

http://arxiv.org/pdf/gr-qc/0310059

Plus there are a lot of followup papers from 2003 thru 2005.

But basically, Peron, you should know how to follow up on your own, if somebody gives you a lead. You are obviously plenty smart and capable to do this. And if you try and need additional help be absolutely welcome to ask, but try first.

If a 13.7 billion year old observer, located in a region of space that we see as the cosmic background microwave radiation, sees the Milkyway region as cosmic background microwave radiation, how do they see the microwave background radiation that we are currently seeing when we look in the opposite direction?

They will have to wait, won't they? The photons that are just now today reaching us from the east, most of them will pass on by us and will continue---many years later arriving at the telescopes of the people in the west.

Unless, there are always these awkward extra complications, unless...unless the expansion of distances is so rapid that it thwarts the photons and doesn't allow them to reach the people in the west.

It's 11 PM here and I'm getting sleepy earlier than usual. You are asking good questions all right. Just maybe faster than I can handle. If it gets more than I can cope with, someone else will help or I will tell you.

http://www.astro.ucla.edu/~wright/cosmo_02.htm#DT

 

The fourth diagram on the linked page, shows space plotted using known observations and fact.

My favorite of those particular diagrams is the third, with the PEAR-SHAPE light cone. Horizontal distance in that picture corresponds to the actual distance at that time, if you could freeze expansion, and measure it by radar.

But I think we both realize that cosmological distances are inferred, using a model. One measures redshifts and infers distance. Have you used one of the calculators to convert redshift to distance? Ned Wright has a good one. Google "Wright calculator".

...Take a region in space which we are now seeing as microwave background radiation. It cannot be both a region of space 300,000 years old, a flux of hot hydrogen atoms, AND a region of space, 13.73 billion years old, which looks like a galaxy. Its image is what we see and what is real to us, its gravity and photons are reaching us now. All regions of space should be able to be considered, from the same perspective. Our perspective.

That sounds like a philosophical point of view. The universe is the photons etc that are arriving to us today. One could argue for it philosophically. But as a practical matter, cosmologists don't think that way. They construct a model of the way the universe IS today and the way it was at each moment in the past. They typically use the "frozen expansion" distance or socalled proper distance, to locate things in the model.

It is a collegial way of thinking. Imagine that there are observers scattered all over. Observers in every galaxy. Construct the common reality that we are all looking at, and could most likely agree on. Admittedly our friends the other observers are imagined. They may not exist and even if they did we might never be able to communicate with them. But the construct is as if it were to be shared by all observers. It is not just about the photons arriving here today at Earth observatories.

Do you know about universe time? Cosmologists have a criterion of rest, being at rest with respect to the ancient light, the expansion process itself.

And there is a corresponding notion of now. Of synchronicity. In pure relativity you don't get that, but in cosmology you do, because you have matter in the picture, not just pure geometry. So all the observers can have synchronized clocks and agree on a common figure for the age of expansion, 13.7 billion years or so.

Well, almost 12. Time for bed.

Hi Tar,

this is an interesting thread. Shows careful unopinionated hardworking imagination on your part. I'm impressed by the thoughtful response by Spyman, Severian, Sisyphus, Bascule...and others.

For several weeks running, I've been preoccupied by real-life demands and trying to learn some unrelated stuff, so missed all this good discussion!

Just now noticed a post you wrote recently in an astro thread by Purin..(spelling?) where you indicated you thought you had gained some understanding of the conventional cosmology picture---confusion reduced, but still some confusion.

If you want, you could summarize for me briefly in simple language one or two points where you are still uncertain or puzzled. This would save me having to sift through the posts and guess what still might be bothering you.

Also I see you have what I'd judge to be philosophy of science type sophistication. You realize that science is just a community of mere humans, with an ethic of behavior, a selfselecting aristocracy, a tradition that serves as rough guide. And the models change over time. In cosmology folks only recently began getting lots of good data to adapt their model to, it is a very exciting time in cosmology because it only recently became a truly observational science.

As sophisticated observer and questioner, you realize that we cant say the current standard cosmo model is TRUE, heh heh. Folks just do the best they can and stumble on, improving as they go.

But frankly it is extremely interesting and worth understanding, the current fit to the data is impressive. There are subtleties that take some effort to understand.

It seems to me like you want to learn what the current picture is, while retaining mental reservations about believing it. That seems to me like the perfect way to approach it. I may be misjudging. I didn't have enough time to read your posts at all carefully.

http://scienceblogs.com/catdynamics/2009/09/water_water_everywhere.php

http://marsprogram.jpl.nasa.gov/mro/newsroom/pressreleases/20090924a.html

Photos of fresh meteorite craters show a reflective white material which goes away over the course of a few weeks or months. This is in the mid-latitudes. So it is not limited to near the poles.

The depth of the crater can be estimated at a few meters. These are small meteorite impacts. Spectrograph confirmed that it is H2O

The ice layer is apt to be fairly widespread.

Scr*w the moon. Mars is where the real water is.

It's controversial still, as far as I'm aware.

Ned Wright criticized Kashlinsky et al's paper.

At first I thought the crit would probably stick and Kashlinsky "dark flow" was effectively tossed out.

But then Kashlinsky answered the criticisms and made some corrections and admitted some of Ned Wright's points. But it seems to still stand.

They say they tested out to a distance of 1.3 billion or 1.4 billion lightyears.

I don't know how solid the statistics are and how much random variation.

The average speed of the drift, according to them, was around 600 km per second.

Have to keep in mind that it is controversial. Hasn't been confirmed by any other study that went out such a large distance.

It has been known for quite a while that there was an average motion in our immediate neighborhood (Virgo Cluster and surrounding smaller stuff) in that Hydra etc direction of about that size like 600 km/'s.

What Kashlinsky is saying is that this known motion extends 10 times farther out, includes a much larger flock of galaxies.

It is still not ALL galaxies. The catalog they used only goes out to like 1.4 billion LY, present distance. And we actually see galaxies out much farther.

Like redshift z = 7, corresponding to a present distance of about 29 billion LY.

I don't know how far out their method of estimating the speed of a galaxy through the CMB would be valid. At this point I'd be cautious about drawing any conclusion.

Maybe someone who has a more recent source will give us an update on this.

Here's a Kashlinsky et al source paper:

http://arxiv.org/abs/0809.3734

Published in Astrophysical Letters October 2008.

Anybody else hear the speech?

Strong, I thought.

...

http://en.wikipedia.org/wiki/Big_Rip

...

Often it's really helpful to quote Wikipedia---they have some excellent articles. But every now and then they have a bad one. Here they mix up w and omega. The italic w does look like the lowercase Greek letter. And they cite a single peer-reviewed source article and copy just one equation from it----and screw up. They don't copy it right, so they would get a negative time between now and big rip.

You might want to check the source they cite. It is from 2003 and one of the authors is Marc Kamionkowski. They give a link.