Measuring the universe

Roy Wilson — Tue, 09 Jun 2009 01:54:13 GMT

If the calculations of the effect of "dark energy" on the expansion rate of the universe is found to be different over time, then estimates of the age of the universe could be highly speculative. Perhaps some more thought about the nature of "dark energy" is in order. Until "dark matter' and "dark energy" are better understood, our understanding of the universe itself may be highly speculative.

Measuring the universe

Rich in G'burg — Tue, 09 Jun 2009 02:36:13 GMT

"Right now, the [Hubble Constant] is known to an accuracy of about 10 percent."

Accuracy to only 10%? Or is it really plus-minus 10%?

[ALAN ADDS: Hmm, I see what you're saying. It's plus or minus 5 percent, based on my reading of the figures. I'll change the reference in the story to make it clearer. Many thanks...]

Measuring the universe

Raymond Belanger, las vegas Nevada — Tue, 09 Jun 2009 02:52:55 GMT

Our perception of time is our way of seeeing, or hearing, motion. to stop time you would have to "STOP MOTION" [impossible] MOTION on the other hand, is energy, which is what everything is MADE OF. So why would you want to stop time?

Measuring the universe

Mark Anderson, Detroit, Mich. — Tue, 09 Jun 2009 03:16:30 GMT

considering relative perspective reducing the margin of possible

error seems to be a noble effort as we measure the infantisimal

vibrations of subatomic particles our measurments can affect

those very vibrations therefor when measuring the vast distances

approaching the limits of visible light will those distances have an

affect on our measurments or visa versa

Measuring the universe

Matt, Toronto, Ontario — Tue, 09 Jun 2009 03:32:51 GMT

I'm pretty sure your numbers are off on the visible distance of Cepheid type stars, you mention that the low luminosity ones are only visible from 100 light-years, but the nearest star to us is about 40 light-years and we're obviously talking about distances much farther than that.

[ALAN ADDS: Actually, the nearest stars beyond the sun are in the Alpha Centauri system, about 4 light-years away.]

Measuring the universe

Mark, Amesbury — Tue, 09 Jun 2009 04:45:02 GMT

Stupid scientists - every time they can't explain something with their current model, they 'invent' a mechanism to shoehorn the unexplained phenomenon into the model. Gee - would it be a reasonable idea to question the model.

The standard candle approach to explaining expansion is flawed. If it was true, all galaxies would be all flying away from one another, yet there are numerous know cases where galaxies are flying towards each other - even crashing into each other. Ya can't have it both ways. Also, the pattern of redshift doesn't make sense. It would only make sense if the Earth were in the exact center of universe, which we know is not the case.

Yep, it is much more likely that we are wrong in our understanding. Same as ether years ago.

Measuring the universe

Byron Raum, Beverly Hills, CA — Tue, 09 Jun 2009 05:48:00 GMT

I think there's a "million" missing in the distance, so it's about 325 million light years that ULPs are visible for.

[ALAN ADDS: ULP, you're right. I've made the correction, so sorry about the error... And sorry that I was so dense about recognizing it.]

Measuring the universe

Jason — Tue, 09 Jun 2009 09:17:36 GMT

on the shoe horn comment.. I suggest you read this article:
http://mattjwest.newsvine.com/_news/2009/06/07/2905831-creation-this-agnostics-point-of-view-eternal-informational-universe

Measuring the universe

bryan park, canada — Tue, 09 Jun 2009 12:29:15 GMT

i dont get it

Measuring the universe

Ryan, Raleigh, NC — Tue, 09 Jun 2009 12:46:43 GMT

@Mark from Amesbury,

At large distances of at least several megaparsecs, even galaxies that would be traveling in our directions would still end up traveling away from us, because the space in between is expanding at a rate higher than the velocity of the galaxy. So the "standard candle approach" works just fine over long distances (obviously, within a certain degree of error).

As for the Earth needing to be in the exact center of the universe, we are, in fact, in the exact center of our observable universe and, from our perspective, everything (that is far away enough) is moving away from us. This is because the expansion of space occurs everywhere, not just from some orgin point with the initial "explosion" happened. There was no explosion, the Big Bang was, and still is, a rapid expansion of space from all points in the universe simultaneously. No matter where you are in the universe, it looks like everything is traveling away from you. That is why redshift works.

Measuring the universe

Jim Geiger Greensboro N. C. — Tue, 09 Jun 2009 12:49:31 GMT

Astronomers want us to believe they have the answers regarding the size, composition, age and expansion of the universe, and if the TRUTH was known, they are guessing.

Measuring the universe

Nik D, Cincinnati, OH — Tue, 09 Jun 2009 13:15:40 GMT

It seems that distances are being measured, based on the fact (or assumption?) that light/electromagnetic radiation travels in a straight line.
Is it possible that a galaxy might actually appear to us as being in different places and thus at different distances?
eg:
Light from a galaxy "X" that does travel in a straight line, reaches us, thus helps us conclude "X" is so many light years away.
Is it possible that some of the light from the same galaxy "X" travelling in a different direction being "bent" by the gravitation lens effect of many other galaxies also reaches us, resulting in galaxy "X" appearing to be in a completely different place, and since that light has travelled a much longer path, makes us think "X" is much further away and a completely different galaxy?

Measuring the universe

Patrick, Columbus, IN — Tue, 09 Jun 2009 13:22:40 GMT

Could someone please explain to me, like I was 5, how if all things came from the big bang, then why are there some galaxies flying toward each other, like say Milky Way and Andromeda?

Measuring the universe

Paul Scher, New York, NY — Tue, 09 Jun 2009 13:24:05 GMT

So anyway, it's raining outside. When we consider the infinitesmal part of the world that we live in, and then consider that our solar system is just a mote in a vast galaxy, and then realize that the entire Milky Way is but a dot in the measureless universe, it's time to realize that there are some things that are beyond measurement, "A Mote in God's Eye".

Measuring the universe

Eddie McEvoy Scotland — Tue, 09 Jun 2009 13:41:07 GMT

Dark Energy, Dark Matter ? When I was at school, we put a balloon in a bell jar and evacuated all the air from around the balloon. The balloon expanded in all directions. Surely we should be also looking for a similar effect such as this to explain the expansion of the Universe, not looking for some exotic substance that should be detectable, given the vast amount of the staff that should be littering the Universe!

Measuring the universe

Darrell Messbarger — Tue, 09 Jun 2009 13:47:09 GMT

Mr. Belanger asks a very good question? I have an answer that may or may not be a possibility, but would dearly love to figure out a way to test it experimentally. If you could stop universal motion would time stop? If space and time are inseparable, how is gravity linked?

The enormous distances that are being added to the known universe with every tick of the clock must have more physical impact than just size.

Measuring the universe

Brian Butler — Tue, 09 Jun 2009 13:57:29 GMT

Ha. Yes, the ongoing theories of the greater, and also of the lesser with quantum theory are so reminiscent of the old theory of Atlas holding up the world. When the "up-to-date" and intelligent scientists realized that Atlas couldn't be just floating in the universe, they hypothesized that he was standing on something. What? The back of a giant turtle, of course. When science realized that the turtle had to be supported by something, they hypothesized a giant sea for him to be swimming in. We're just doing the same hypothesizing in this age about the large and small ends of creation, except with Hubbles, bubbles and strings instead of with turtles.
No offense Albert, I DO like your idea on wearing the same sweater over and over.

Eventually we'll learn that the physical universe (an absolutely mental creation) is continually recreating itself.

Measuring the universe

Scott, Dayton, Ohio — Tue, 09 Jun 2009 13:57:56 GMT

Alll you need is a tape measure with no beginning and no end to measure the universe as the title implies, these measurements described seem to be coming along well for relative disyance between objects. Remember by definition the universe is everything that ever was, is or will be has no edge since if you go one inch beyond the edge it is till thew universe:)

Measuring the universe

Doug, Pasadena, CA — Tue, 09 Jun 2009 14:01:29 GMT

A million light years here, a million there, soon you are talking real distance.

Measuring the universe

Jym Allyn — Tue, 09 Jun 2009 14:21:27 GMT

Is this the Genesis version of the Hubble Constant or the Deuteronomy version?

(I couldn't resist the sarcasm. Bless you for attempting to bring rationality to the world.)

Measuring the universe

Aegliss Shelbyville TN — Tue, 09 Jun 2009 14:33:45 GMT

This page is linked as the "Comic Log"
I thought you were going to give us jokes.

Like,... It's been a rough day and gravity is really bringing me down.

or

A proton walks into a bar. The bartender says.. "What'll it be?"... The proton says, "Nothing. I'm fine. Thanks." ... The bartender says ... "But, Are you sure?"... The proton says, "I'm positive"

Mwahahahahaha

4 light years away to the closest star? What is the nearest star with a planetary system?

I usually don't reply to these, just read them,.. but since I'm replying .. steve smith... you da man

Measuring the universe

Frank Brownback,Butte,America — Tue, 09 Jun 2009 15:33:19 GMT

These new findings that improve accuracy are incomprehensible until you provided the anology of the quarter on the desk at a distance.Is the law of entropy so good that E(light energy)is entropied to E(dark energy) and 'stored' in DM(dark matter) to become the next 'point' of a new BIG BANG that may set a different laws of physics fo a new universe?Maybe that dark energy is a converter that stops space time and our other ten dimensions!

Measuring the universe

Ted, Palm Bay, FL — Tue, 09 Jun 2009 15:50:31 GMT

Why would anyone even care about the size of the universe, which is supposed to be infinite in nature? Besides, the only time you'ld be interested in the distance to something is when you're planning to go there. Since we haven't even been to the moon (250k miles) in over three decades the point is moot, and will remain that way for hundreds, if not thousands, of years.

Measuring the universe

Eric, Salinas, CA — Tue, 09 Jun 2009 15:55:08 GMT

An excellent informative article Alan! It's nice to see the scientists come up with better methods for determining the distance to galaxies. I do hope that they can eliminate the uncertainty in measuring the Hubble Constant. I find it interesting keeping up with how scientists are trying to discover the truth behind dark matter and dark energy. I enjoy the science shows that deal with these matters, saw Wendy Freedman on some of them.

Measuring the universe

JD, Austin, TX — Tue, 09 Jun 2009 15:59:27 GMT

Mark 'stupid scientsts' commenter. You need to take an astronomy course. The issues you are worried about are dealt with in Atronomy 101 and the answers are simple. Neither you or the scientists are stupid :-) You simply have not been taught the answers. Go forth and learn. It's a lot of fun.

Measuring the universe

B.K., Detroit, MI — Tue, 09 Jun 2009 16:01:23 GMT

"What's the matter?"-- Einstein

Measuring the universe

Diana Redfern — Tue, 09 Jun 2009 16:39:20 GMT

Hello fellow pet lovers. I have a 4 lb.Maltese named Ellie-Jo. She flies everywhere with us. I have found how you are treated on the plane depends the flight att. I have had people who think she is adorable to YOU BETTER NOT TAKE THAT DOG OUT!!! Maltese do not shead. They are very good for people with allergies. I don't mind paying for her to fly with us, but it gripes me that a child can sit on it's mother's lap for free! What about saftey? I passenger cannot unbuckle and a child is allowed to sit unprotected? On one flight to Ft. Lauderdale I had a child climbing all over me the whole trip. The flight att, ask the mother to hold her, Guess what shr couldn't speak English!!! And of couse there wasn't an empty seat that I could move to. Anyway happy traveling everyone.

Measuring the universe

Mark, Washington DC — Tue, 09 Jun 2009 16:53:04 GMT

I don't pretend to understand the math that shows why Dark Matter and Dark Energy need to exist, but I still get the sense that the theorists are ignoring a key rule - parsimony. Why introduce it as a necessary part of our theories about the Universe before it's actually been seen or observed directly? It almost seems like a plug in the equation to get the model to fit behavior observed in nature. Shouldn't we also consider rebuilding the model altogether to track what is happening? Maybe our understanding of gravity itself is flawed at extreme distances? Maybe our understanding of how much normal matter exists is wrong - we're not capturing it all in our observations. Maybe the nature of the Big Bang is not what we think it is. There are tons of reasons other than Dark Matter and Energy to explain why our models don't match reality. Someone in the community needs to stand up and call a time out.

Measuring the universe

brian norwood — Tue, 09 Jun 2009 16:57:50 GMT

Why is dark energy called a force which is "pushing"the universe outward? Could it be another force outside the bounds of the universe which is "pulling" it?

Measuring the universe

Tim Rommes, Washington, UT — Tue, 09 Jun 2009 17:06:25 GMT

Mark, Amesbury, I, also, am not fully satisfied with the redshift data. However, as presented it makes coherent sense. What you mistake for being applicable really only reflects an angular difference. Conduct a thought experiment, or a real one. Have a bunch of cars grouped together in the middle of a dry lake bed. Equip each with a gps recorder. At a specified time have them radiate out. Over time have them accelerate at the same pace. Assemble your data. You'll find that the nearer cars, while accelerating just as much as all other cars, were accelerating away from you less than the farther cars. The nearer cars are going almost the same direction so they only slowly drift away. The farther cars are moving away from the common point at a much greater angle. A lot more distance opens up between cars moving perpendicular than between cars moving 1 degree apart over the same time in those conditions. If you reconduct the experiment with three sets of cars, the farthest out being slightly faster and the closer in being slightly slower than the middle set, then with the same accelration rate the car in front of you will still slowly accelerate away, the car behind you will still seem to slowly accelerate away and we have the appearance of being in the center of everything. Reconduct the experiment with oodles of waves of cars and allow those cars to radiate out in 3D and you get what we see with galaxies. Red shift is about relative motion and relative to us we are in the middle, that's why you get that appearance.

Measuring the universe

Brian M. Aston, PA — Tue, 09 Jun 2009 17:33:15 GMT

" Also, the pattern of redshift doesn't make sense. It would only make sense if the Earth were in the exact center of universe, which we know is not the case."
====
sorry but that is a flawed view. Since Everything in the universe is included in the fabric of space-time(think spandex or even better a rubber ball being inflated) everything is in the grand sense of things moving away from each other.

Now as to what you point out as a flaw of galaxies crashing together, the universe can be expanding and streching the fabric but the galaxies still move around in the fabric. If you take a piece of spandex and start to strech it out flat then drop a couple of weighted balls on it they will still roll around and run into each other even as you strech the fabric making the surface larger.

Measuring the universe

Dan Snyder, Bellevue, WA — Tue, 09 Jun 2009 18:02:20 GMT

Mark: the observed expansion of the universe does not assume that Earth is at the center. The expansion would look the same from any point. Imagine a balloon with a bunch of dots drawn on it. If you blow the balloon up, all the dots move away from each other. It doesn't matter which dot is in the middle. From the perspective of any dot. all the others are moving away.

As for the fact that some galaxies are approaching each other, yes that's true. In the real universe, the dots on the balloon are themselves in motion. It's like rolling marbles around on a pizza dough while stretching the dough out. Some of the marbles will end up moving toward each other, but the dough is still expaning.

Measuring the universe

Sarah Miser — Tue, 09 Jun 2009 18:23:08 GMT

It seems like there is a lot of guess work going on here. Yea, when we figure the around 10% the numbers work, but we need to figure this out exactly to move forward.

Measuring the universe

Bud, Denver, Co — Tue, 09 Jun 2009 18:49:02 GMT

I have a question about "dark energy" if the expansion of the universe is increasing over time, how do we know it isn't TIME that is slowing instead? Is it possible that as the black hole at the center of the galaxy increases in size time slows within the galaxy? I never hear this mentioned and I wonder why.

Measuring the universe

JOSE CRUZ CRUZ 1606 HARBOUR OAKS RD, TUCKER G.A. 30084 — Tue, 09 Jun 2009 18:56:38 GMT

I LIKE THIS INFORMATION , IF POSSIBLE SEND MORE INFORMATION , ME GUSTA TODA ESTA INFORMACION REFERENTE A LAS COSAS DE EL ESPACIO,LAS GALAXIAS, LOS ASTROS, LOS PLANETAS Y TODO LO RE SE RELACIONA CON EL UNIVERSO DIOS LOS VENDIGA EN TODO EL TRABAJO QUE USTEDES DESENPENAN GRACIAS .... TANKS

Measuring the universe

Chad, Las Vegas NV — Tue, 09 Jun 2009 19:01:57 GMT

In response to Mark in Amesbury..

As I recall from my highschool years.. it was only a few hundred years ago that almost everyone believed that the earth was not only flat but the center of the universe.

Although I agree that our current understanding of the universe and all it's pieces and parts is not completely accurate, we do have a far greater understanding today than we did just 20 years ago. As long and curious minds continue to ask questions and new technologies becomes available, we will increase our knowledge of the "Last Frontier".

Measuring the universe

Angela Veltrano, Rincon Indian Reservation, CA — Tue, 09 Jun 2009 19:14:11 GMT

would the error be compouded by the distance? I mean if you are off 1/2 inch at the beginning of a bridge by the time you cross the bridge it is more like three feet.

Measuring the universe

Thomas Ashby — Tue, 09 Jun 2009 19:21:30 GMT

Byron Raum...yes considering M81 is some 2 million LY's away.

I think this is all based on absolute magnitude. The magnitude a star exibits at 10 parsecs or about 35 LY's.
The sun has an absolute Mag of +4 while it's visual magnitude is -25. A difference of 1 magnitude between 2 stars means one is 2.5 X's brighter or dimmer than the other and the increase or decrease is logaritmic.

I think distance is brought into this by somehow relating magnitude and the inverse square law for distance and brightness..1/d**

How this all relates to cepheids I really don't know.

Measuring the universe

George Cernigliaro,Newton, MA — Tue, 09 Jun 2009 19:21:34 GMT

To Mark of Amesbury,

It's OK to shoehorn stuff into the model until it doesn't work anymore. That's how science progresses; it's part of the process of eliminating experimental models as a viable theoretical approach. At some point, the model will not be rational.

It's much like the retrocycles used by the accolytes of Aristotle to explain the apparent retrograde motion of the planets, relative to our line of sight on earth. It was only when Copernicus came along with a more elegant heliocentric model did the Earth-centered universe go by the boards. Of course, only in hindsight, Aristotle's model looks like the dog it is.

In much the same way, when the final model of the universe is elucidated, as may happen someday, will all the other models look nieve and unsupportable.

Science is a deeply human practice, but it is a work in progress, and will be for a very long time.

Scientists, being the humans they are, will hang on to a concept for reasons technical and non-technical. I've heard it said that science progresses by a generation or two only when the major influential people in it die off, leaving a new generation to put forth their new ideas.

Maybe you'll be one of them, eh?

Enjoy the ride!

George Cernigliaro

Measuring the universe

JediMaster Qui Jin — Tue, 09 Jun 2009 19:52:22 GMT

I often think of the possibility that light speed may not be as constant as we believe. That it is possible that light may have traveled faster or slower in the early universe thus showing our lack of understanding on light speed and how it relates to how we measure these incredible distances.

Measuring the universe

Qui Jin, Philly — Tue, 09 Jun 2009 19:59:42 GMT

How can an atom be in two places at the same time. Is it possible that on the atomic level that things can actually travel from one space to another without neccesarily traveling through time.

Measuring the universe

Matt K, Los Angeles, CA — Tue, 09 Jun 2009 20:19:06 GMT

Dark energy is interesting because it's such a large unknown. I always wonder, since evidence for its existence is based on the standard candles, how do we know there's not something wrong instead with our understanding of the intrinsic brightness of the candles?

Measuring the universe

DrB, Daly City, CA — Tue, 09 Jun 2009 20:35:23 GMT

Mark -- the metric expansion of space is a large-scale phenomenon, i.e., galactic superclusters are receding from each other. On a galaxy scale the effects of gravity predominate yielding collisions.

You don't provide any details as to problems inherent in red shift so can't clarify anything there.

Measuring the universe

Scott — Tue, 09 Jun 2009 21:14:23 GMT

I am fascinated by the assortment of wisdom contained in all of these contributions. It better than watching the Discovery Channel!!
Thank to all.

Measuring the universe

Alex Dickerson — Tue, 09 Jun 2009 21:22:28 GMT

bud in denver colorado, your time question is actually the "runner up" if you will in theories concerning expansion, and a very good theory that doesn't rely on unseen forces of dark matter or dark energy. It was origionally conceived to replace the disproved "tired light" theory. And i agree with those of you who question the existance of dark energy and dark matter. I'm not saying its not there (something like ten million tons of matter, i believe, careen into our atmosphere every day, matter that doesn't emit light, that is until it burns up as a meteor), but it is as likely or more likely that these phenomonon we witness are unidentified properties of forces we already recognize, like gravity.

Measuring the universe

Tim Rommes, Washington, UT — Wed, 10 Jun 2009 00:31:12 GMT

Bryan Park, Amesbury, you’re not alone.

Nik D, CinCinnati, OH (6/9, 0915)
Even if the light got curled around like a crazy straw before it got to us it would still red shift. And yes, it would look like whatever direction it’s inbound to us is the direction it’s from.

Patrick, Columbus, IN (6/9, 0922) Early plasma would have grouped together into swirling masses. Pieces that separated would fly off in non-radial directions. Those blobs would effect the trajectory of everything around them over time. So in the interior, particularly, you wind up with a lot of complex gravity shifts that sling matter all over. Also, and lesser, the effects two blobs have on each other as the move out nearly parallel but at slightly different speeds. Their gravities will cause them to cross, again introducing non-radial movement. Much like the effects planets have on each other.

Regarding the question posed by Mr. Belanger: If you stop motion time moves at its fastest.

Measuring the universe

Jan in Birmingham — Wed, 10 Jun 2009 00:39:53 GMT

Did I miss something, or ....I see in my mind a rocket sitting on a pad, then ignition, and the rocket slowly lifts off the pad, and as it gains height it gains speed, pulling away from the pull of gravity and gaining speed. If all matter at one time was compacted into a single mass, then started to fly apart (the big bang), I think it may well have happened like the rocket lifting off the pad, slowly, until it overcame the gravitational pull, then accelerating as it achieved more distance from the other fragments.

Measuring the universe

Jan in Birmingham — Wed, 10 Jun 2009 01:03:48 GMT

To clarify, the velocity of the matter flying off in different directions following the big bang may not have begun at its highest rate of speed. Rather, they billions of pieces may have separated themselves from their single united mass much more slowly (i.e., the rocket) than we visualize an exploding bomb.

I can well imagine the extreme gravitational pull that would have been necessary to hold all matter together, until it reached critical mass and then disintigrated (BB).

Measuring the universe

Thomas Ashby — Wed, 10 Jun 2009 02:56:04 GMT

Ok, here is tje basics of distance and cepheids

d = 10 (m - M + 5)/5 ; m= apparent magnitude, M = absolute magnitude

http://outreach.atnf.csiro.au/education/senior/astrophysics/variable_cepheids.html

Measuring the universe

Fred Smith, Ventura, ca — Wed, 10 Jun 2009 03:12:48 GMT

Patrick: Re Milky Way and Andromeda collision. While the distance between the two galaxies is about 3 million light years it is small compared to the universe and the gravitational attraction between the two decreases the distance faster then the expansion of the universe increases it.

Measuring the universe

esskay — Wed, 10 Jun 2009 03:53:49 GMT

@brian norwood: thanks for asking that, I've been wondering about that too...

Measuring the universe

Frank Brownback,Butte,MT — Wed, 10 Jun 2009 04:47:53 GMT

The new Hubble may help awnser some of these questions or give more helpful data?Hope so!

Measuring the universe

terrall w chilcoat - gardnerville nevada — Wed, 10 Jun 2009 06:35:03 GMT

the big bang did not happen in one spot. it happened throughout the universe all at the very same moment. how could this be? because it happened at the very moment that all matter from the previous universe converted back to a neutral nothingness (and time stopped). with all matter gone into nothingness there was no distances. without travel from point A to point B then you have no time. so with no time then you have endless time for something to happen. to the mystic observer the universe would End and a new universe would immediately spring out of the nothingness. maybe a hole or bubble (string theory) would appear in the nothingness (sounds like Genesis doesn't it). the inside of the hole (bubble) being positive and outside (the nothingness) being negative. when out universe collapses into nothingness then time will stop again and the phoenix like process will start again. this is NOT parallel universe thinking. when matter is completely gone then time no longer exists. there can be no connection between these universes (plural intentional). meaning these startings and stoppings are eternal.

I can be reached at t@raa.cc

Measuring the universe

George Jones, Saint John, New Brunswick — Wed, 10 Jun 2009 13:00:36 GMT

Some stuff about dark energy and dark matter.

Dark Energy. It was long thought that the pull of gravity inexorably slows the rate of expansion of the universe, but, since 1998, observations have shown the opposite; for the last several billion years the rate of expansion of the universe has been increasing. Many physicists say that a source of dark (unseen) energy is needed to drive this counter-intuitive acceleration.

This dark energy could be:
the energy of the vacuum predicted by quantum theory;
a hitherto unknown energy field;
a previously unobserved property of gravity;
or a combination of the previous three possibilities.

How could cosmic acceleration be caused by gravity? When we examine the world on levels far removed from everyday experience, we often find that our expectations are wrong, and we could be wrong about the universal attraction of gravity. At "close" range gravity is attractive, but, over cosmological distances and times, gravity might be repulsive. This is compatible with Einstein's theory of gravity. In this scenario, nothing is needed to counteract gravity, as it is gravity itself that is causing the acceleration of the expansion.

Current observations are consistent with all these possibilities. Without a workable theory of quantum gravity, we can only speculate about the energy of the cosmological vacuum, so I think that a workable quantum theory of gravity is needed to distinguish between the various possibilities.

Dark matter is needed to explain the motions of stars within galaxies, and the motions of galaxies within clusters.

Stars revolve around the centres of galaxies, with our Sun taking about 230 million years to complete one orbit about the centre of our galaxy. Because a star's orbital speed about a galactic centre depends on the gravitational force that holds the star in orbit, and because gravitational force depends on the amount of matter in a galaxy, measurements of stars' orbital speeds "weigh" galaxies.

These measurements indicate that most of the masses of galaxies are dark, that is, not visible as hot, glowing matter. Motions of galaxies in clusters of galaxies also indicate this. This doesn't seem to be unexpected, as galaxies could contain a lot of material that is too cold to glow. Theoretical studies of the production of chemical elements after the Big Bang, together with observations of cosmic abundances of chemical elements today, however, show most of the dark matter is not made of the same type of matter, protons and neutrons, that make up ordinary stuff like people, planets, and stars. This also rules out black holes that formed from the collapse of stars that were originally made of protons and neutrons.

Physicists think that dark matter requires particles that have yet to be observed directly.

Measuring the universe

Alan Cordeiro, Edmond, OK — Wed, 10 Jun 2009 14:14:05 GMT

If we assume that just before the Big Bang, the sum total of the universe was zero, then it is a reasonable possibility that the Big Bang resulted in the creation of equal amounts of positive and negative energy, as well as matter and antimatter. It may be that there are more dimensions to the universe than we can see, and dark matter and dark energy are predominantly found in those other dimensions. This would explain why there is so little antimatter found in the visible universe--it's all in the non-visible portion. I also suspect that the current expansion is part of a repeating cycle, like a sine wave, and the universe will eventually collapse back on itself, then repeat the Big Bang.

Measuring the universe

Bud, Denver Co — Wed, 10 Jun 2009 14:28:30 GMT

Alex Dickerson,

Wow, Where can I read more about this runner up idea?

Measuring the universe

Fred Leserowitz — Wed, 10 Jun 2009 18:19:12 GMT

Measuring the universe? What For? Does it help you know more about what is doing here to know that the stars are another 2 or 4 milllion light years away?

Expansion of the universe? I have a simple question. If the universe is expanding, what is outside of the universe that the universe is expanding into? And if there is something that the universe is expanding into, it that something expanding or shrinking?, and where did it come from?

Measuring the universe

Frank Wilson, Seaside, CA — Wed, 10 Jun 2009 18:48:03 GMT

To add to Brian Butler's comments, that the universe is continually recreating itself, the constant recreation of the universe will cease on 10-11-2011 (it is said).

Measuring the universe

Kip Hansen Portland, Or — Wed, 10 Jun 2009 19:11:47 GMT

While on the subject of measuring the universe... I have a problem with the Big Bang Theroy. With the latest Deep Feild pictures fromHubble, they are saying that they are going back 12 Billion years or so. The galaxies that are pictured there, while close together, are rather mature and organized galaxies. With the light taking so long for it to get to our current location, and for the claims that they are "seeing" 500 million years after the Big Bang, our galaxy would have had to travel some 10 billion times faster than light to get that far ahead to observe it now.

In my opinion, the universe must be immeasurably vaster than what is currently thought of. There my have been a Big Bang for our current area, but then there may be multiple areas where mater coalesces and condenses until it produces another local Big Bang, scattering matter in all directions again like the ripples on a rainy pond.

Measuring the universe

Bhas, Kathmandu, Nepal — Wed, 10 Jun 2009 19:13:17 GMT

Hello,
I have seen UFO's 4 times, all different from missisauga toronto in summer of 2005 ( energy), have seen a dark image floating same time( it reminded me of ghost in The Grudge), Maybe that was related to dark energy, huh. I have also seen a shooting star very near to the earth that burst into beautiful blue with several fluroscent sticks into it. I have also felt hand out of nowhere, more like being inserted into me ( could be my karma- thinking one)
I believe so much can be learned from fire, and it is also impossible to catch fire- like time.
I hope whatever happens, it happens for good of mankind and living beings and that everyone can learn and understand.

Measuring the universe

Bhas, Kathmandu, Nepal — Wed, 10 Jun 2009 19:17:46 GMT

Oh yeah when I saw the ufo's and the moving image like a shadow, I was living with Mexican family. I 've heard there are many ufo sightings in Mexico. Maybe the energy was around them.

Measuring the universe

(R.Earl Brown, Seaside,Oregon) — Thu, 11 Jun 2009 09:48:00 GMT

Telescopic voyage's into the space around our world, allow a look back at the previous state of a given star or galaxy. We see none of it in real time. We may witness an event looking up at the night-sky that happened two thousand-years in the past, if not six-billion-years ago, simply because the light from the event took that much time to reach Earth. Be it the ignition of fusion at the birth of a star, the detonation of a Super Nova, or the transit of a planet across the face of its parent star. All go unseen by us until the light from the given event, or reflected from it, reaches Earth.
Lately I read about observations of White-Dwarf Stars, which are a constant in that they characteristically require a known and exact-mass to go Supernova. Ergo the known mass of these Stars, along with a measure of their brightness, can be used as a reliable mark of their distance from the Earth.
Further, by measuring the”Red-shift”or Blue-shift of the light of White-Dwarfs during these detonations at various distances, indicate that the known universe is expanding as expected, but unexpectedly, the rate of that expansion is not decreasing as might be expected even , but is instead increasing. The question, as I understand it, is this:
Does matter from the Big-Bang continue to expand outward until the relentless attraction of their mutual gravities over time slow down the expansion, eventually stops the expansion, and finally draws all matter back toward the center for yet another crushing compression,”Big Crunch”(Singularity) and yet another “Big-Bang.” Or will matter from that first and only known great detonation we speak of as the“Big-Bang,” continue to expand forever? Depending on what you read, scientists' can find just seven to thirty percent of the mass in the universe required to explain this increased rate of expansion, Something we cannot see or don't yet understand is causing the expansion of the universe to increase at a faster rate. Thus the theory of dark matter and dark energy, which I have seen explained as a sort of opposite gravity
Suppose the universe, as we know it, is in fact far-larger than we see with Hubble, Shandra, etcetera. Is our Big-Bang only a local repetition of expansion and contraction happening alone, or is it a player among forces that are neither invisible, nor dark necessarily, but are simply too far away to detect. Stars, Solar systems, Galaxies and Clusters of Galaxies exerting their combined force of gravity on the outskirts of our knowledge of the universe by virtue of their incredible numbers, and despite their great distance's, yet too far away or too “recent” for us to yet detect by their light. Could matter in a universe that extends beyond our view, be lending its gravity to the increasing rate of the expansion of our universe, and by doing so, be “that” which suggests the existence of “Dark Matter and Dark energy”?
When was it accepted that the universe is the size we now see? Wouldn't ejecta from a wider and surrounding universe born of many “Big Bangs in a presently unknown and far away extension of “our” universe, create the conditions we now accredit to Dark Energy or Dark Matter ? Could the increased rate of universal expansion be explained by the gravity from far outside “our” known universe in the form of Galaxy-Clusters, dust, stars ext. that were once far outside “our” Universe presumably traveling toward us from other far away sectors where other big-bangs' have also happened. close enough now to be adding attraction to the matter from our Big-Bang which should be decelerating as physics dictates. We cannot see back even to our own Big-Bang now, but is it possible we we may begin to see new-light from new-galaxies coming toward us from Singularities presumably from all around us. Does a Big Crunch need necessarily be composed of the self-same material from which it sprung? Or could each “Big Bang” be a collection of new matter drawn in from as yet unimagined distances, as ours for the moment seem to favor being increasingly drawn out perhaps it is on its way to be a part of a “Big Crunch” at distances far beyond our present ability to detect. R. Earl Brown

Measuring the universe

tmak — Thu, 11 Jun 2009 14:46:21 GMT

It is difficult to measure
relative space time dimensions are not the same
may be sphere to cone in equivalence
so in multidiemsional gaussian or eculidean spaces
to many time dimensions, the measurement can varies so much vs actual