Do We Live In A "Stop And Go" Universe?

spaceref.com ^ | 27 May 03 | staff

[RightWhale]

Do We Live In A "Stop And Go" Universe?

Anyone who drives is familiar with the frustration of being caught in "stop and go" traffic, a phenomenon found in urban areas all over the world. Astronomers have found that stop-and-go traffic is even more widespread than that, affecting galaxies throughout the universe. Today at the 202nd meeting of the American Astronomical Society, Robert Kirshner (Harvard-Smithsonian Center for Astrophysics), on behalf of the international High-z Supernova Search Team led by Brian Schmidt (Mount Stromlo Observatory), presented evidence that the expanding universe slowed for billions of years before galaxies began accelerating, like cars that get past a bottleneck.

"Right now, the universe is speeding up, with galaxies zooming away from each other like Indy 500 racers hitting the gas when the green flag drops and the pace car gets out of their way. But we suspect that it wasn't always this way," said Kirshner.

John Tonry (University of Hawaii), principal investigator of the team for the new and collected previous observations reported on today, agreed. "We've been hoping to see this effect of slowing in the distant past. We saw evidence 5 years ago that the expansion of the universe currently is accelerating, but we didn't know for sure what it was doing 7 billion years ago. We are now seeing hints that, way back then, the universe was slowing down."

Astronomers discovered seven decades ago that the universe is expanding, with galaxies rushing away from each other in all directions. Physics suggested that the expansion, which began with the Big Bang, should slow down over time due to the combined gravitational pull from all matter in the cosmos.

Two groups-the High-z Supernova Search Team and the Supernova Cosmology Project-sought to study the universe's expansion by observing distant exploding stars called Type Ia supernovae. At their peak, these explosions are brighter than a billion stars like the Sun, enabling astronomers to see and study them across billions of light-years of space.

Five years ago, both teams announced that their studies of Type Ia supernovae showed the expansion of the universe is speeding up. The accelerating expansion pointed to the existence of an unexplained "dark energy" that permeates all of space.

Those initial findings were based on a few dozen supernovae. Now, the High-z Supernova Search Team has expanded that work to 79 distant and 140 nearby supernovae, some newly observed and some previously studied by observers worldwide. The additional data show with higher precision that the discovery of five years ago was correct and the universe currently is accelerating.

More importantly, Kirshner reported that Tonry and the High-z Supernova Search Team snagged four supernovae so distant that their light may well have left at a time when the universe was still slowing down, before dark energy began to dominate the gravitational pull of matter.

Future plans include doubling the number of well-observed Type Ia supernovae through an ambitious program at the National Science Foundation's Cerro-Tololo Inter-American Observatory. The ESSENCE project (standing for "Equation of State: SupErNovae trace Cosmic Expansion") seeks to make an accurate measurement of the cosmic parameter w, which provides clues about the nature of the dark energy. The parameter w is defined as p/rho, the ratio of the dark energy's pressure to its energy density.

"A better measurement of w will help answer the question: Is the dark energy Einstein's cosmological constant, or is it something else such as the so-called 'quintessence'?" said Chris Stubbs (University of Washington), one of the leaders of the ESSENCE project. "This is an important question considering that about 70 percent of the energy in the universe is dark energy, while only 30 percent is due to matter. Whatever dark energy is, it's the dominant stuff of the cosmos. We can't lose: No matter what we find, this will be interesting."

Currently, the value of w is known only to within a factor of 2. The ESSENCE project will do 10 times better, reducing the level of uncertainty to plus or minus 10 percent.

Adam Riess (Space Telescope Science Institute), as principal investigator for the Higher-z Supernova Search Team, is cooperating with the Great Observatories Origins Deep Survey (GOODS) to look for higher-redshift supernovae using the Hubble Space Telescope's Advanced Camera for Surveys (ACS). That program uses the ACS to find Type Ia supernovae at very large redshifts (and hence large distances), in order to look back even farther in time. The Higher-z project will have the best chance to determine whether the universe really was slowing down before cosmic acceleration kicked in.

[The Shootist]

Yes you're right. I should have said that the faster the cosmological object is receding the higher its red-shift.

SOME objects, M-31 for example are approaching us, and are shifted towards blue, in consequence.

The simplist explanation for differing red-shifts is that the objects you are speaking of have a relative motion towards us, while continuing to recede with the rest of the universe, hence moving away, but at a slower pace. The fast objects have a relative motion AWAY from us combined with the Universal Expansion, ipso facto, they have a higher red-shift.

Heck, we can detect differences in the red-shift of stars in a spiral galaxy seen edge-on. The edge that is moving away is more red-shifted than the edge that is moving closer, while the center of the galaxy has a third measurment. The entire galaxy is moving away but one edge is moving away at a faster rate (higher red-shift) than the other, or the galaxy as a whole.

Also I must ask. Since we can use either Ia Supernovae or Red-shift or a combination of both to determine distance, beyond the 100 ly that parallax allows, how can you be sure that the higher red-shifted objects you mentioned are not, in fact, further away?

Answer. You cannot be certain.

[Swordmaker]

Since we can use either Ia Supernovae or Red-shift or a combination of both to determine distance, beyond the 100 ly that parallax allows, how can you be sure that the higher red-shifted objects you mentioned are not, in fact, further away?

Answer. You cannot be certain.

Bingo. That is why it is healthy to occasionally re-examine the assumptions that were accepted when theories were first created.

[Consort]

I don't like the "stop-and-go" or the "big bang" theories. I'll be glad when they come up with a new pet theory for a change.

[RightOnTheLeftCoast]

Hm. The computer that seemed right snappy five years ago is intolerable to use now. Maybe someday it'll be snappy again?

[RightWhale]

The paper itself is 50 pages long, but interesting if you like to read chem lab reports. Nothing but chemistry, no physics. Maybe that's what cosmology is become, statistical analysis from an HPLC.

[RightWhale]

There was a thread last week about some new physics lab device that can shift a light spectrum just about any amount by a series of internal reflections and an energy input at the right time. Might be related.

[Constitution Day]

BUMP for later.

[RightWhale]

I'll be glad when they come up with a new pet theory for a change

Watch French cosmologists. They are highly imaginative, and natural rebels.

[Virginia-American]

...appear to be quantized...

Isn't this explained by the fact that galaxies are arranged in sheets with voids in between?

[gcruse]

I don't think so. The thing is that changes in the red shift occur at quantum intervals, like the change in energy when electrons change shells. The article at the link could explain better than I could.

[Gary Boldwater]

The Sagnac effect is explained here:

http://www.mathpages.com/rr/s2-07/2-07.htm

Pay particular attention to:

"Special relativity for a Sagnac device are correct and entail no logical inconsistency, the dedicated opponents of special relativity sometimes resort to claims that there is nevertheless an inconsistency in the relativistic interpretation of what's really happening locally around the device in certain extreme circumstances. The fundamental fallacy underlying such claims is the idea that the beams of light are travelling the same, or at least congruent, inertial paths through space and time as they proceed from the source to the detector. If this were true, their inertial speeds would indeed need to differ in order for their arrival times at the detector to differ. However, the two pulses do not traverse congruent paths from emission to detector (assuming the device is absolutely rotating). The co-rotating beam is travelling slightly farther than the counter-rotating beam in the inertial sense, because the detector is moving away from the former and toward the latter while they are in transit. Naturally the ratio of optical path lengths is the same with respect to any fixed system of inertial coordinates."

This shows that the times of flight of east-west vs west-east are unequal.


Now look at my flatcar experiment. The path lengths of the light are unequal, as it is moving. Let's say it's moving with an astronomical radius in a circular path to make it "non-inertial", but for the time of flight it's virtually inertial. According to the Sagnac Effect, the light arrives at two different times because the length of each light path is different. Since the observers see unequal arrival times, but they sense only inertial movement because of the large radius, they can only conclude the speed of light is different in the same "inertial" reference frame.

So how do you resolve this?

FYI:

http://www.physics.umd.edu/rgroups/quantum.html

"The East-West vs. West-East light propagation time experiments are being reactivated with the use of circular scan streak tubes as timing devices. It is hoped that resolution of ~ 10 ps can be achieved. The direct comparison of the one-way propagation times on the rotating Earth has never been done at this precision and in this way. Our knowledge is not secure as to whether the speed of light should be ± c or v ± c, where v is the tangential speed of the Earth's surface. "


US Naval Observatory:

http://tycho.usno.navy.mil/ptti/index9.html

Differential Comparison of the One-Way Speed of Light in
the East-West and West-East Directions on the Rotating
Earth; C. O. Alley, R. A. Nelson, Y. H. Shil, J. T.
Broomfield, J. A. Fogelman, M. A. Perry, J. D. Raynor,
C. A. Steggerda, B. C. Wang, M. J. Chandler, and L. J.
Rueger

[Eastbound]

"ah...Ah...AH...AHHHHH-CHOOOO!!"

[Bloody Sam Roberts]

"ah...Ah...AH...AHHHHH-CHOOOO!!"

According to the "Hitchhiker's Guide to the Galaxy" there is a race of beings called Jatravartids :

Jatravartids

The Jatravartid People of Viltvodle Six firmly believe that the entire universe was sneezed out of the nose of a being called The Great Green Arkleseizure. They live in perpetual fear of the time they call The Coming Of The Great White Handkerchief.

The Jatravartids are small blue creatures with more than fifty arms each, who are therefore unique in being the only race in history to have invented the aerosol deodorant before the wheel.

[Eastbound]

"The Jatravartid People of Viltvodle Six firmly believe that the entire universe was sneezed out of the nose of a being called The Great Green Arkleseizure."

Whoa! Art imitating life? Okay, how did they know? ;)

[6ppc]

Wow! Variable entropy! Looking like we can't depend on anything to stay constant!

[6ppc]

We will find out what is causing this expansion and stop it. We will also find out what makes the stars burn out so quickly. We will make the universe last a million times longer than it would if left to nature, and then we will extend that a million times more.

Soooo...this would be called a "sustainable universe"? I can see algore now...

[JoeSchem]

We will find out what is causing this expansion and stop it. We will also find out what makes the stars burn out so quickly. We will make the universe last a million times longer than it would if left to nature, and then we will extend that a million times more.

-J D Bernal

When we’ve been there ten thousand years,

Bright shining as the sun,

We’ve no less days to sing God’s praise

Than when we’d first begun.

-- "Amazing Grace," by John (no relation to Isaac) Newton.