Is Einstein's blunder right? (Astronomy Magazine)

[Up2Late]

(Now if anyone can explain to me how they came to this determination, "...They discovered that supernovae at a given distance seem to be fainter than they would be if the universe's expansion were slowing down...," if anyone can explain to me how they came to that determination, in two paragraphs or less, I'd greatly appreciate it.)

Is Einstein's blunder right?

Cosmologists find the great physicist's famous error may not be so far off after all.

Francis Reddy
November 23, 2005
(Astronomy Magazine)

In 1917, Albert Einstein added a fudge-factor to his theory of general relativity in order to balance the attractive force of gravity. After Edwin Hubble showed the universe is actually expanding, Einstein retracted his cosmological constant, which he called his greatest blunder. Now, a survey of distant supernovae reveals that dark energy — the mysterious force accelerating cosmic expansion — behaves like Einstein's constant to a precision of 10 percent.

"Our particular observation is at odds with a number of theoretical ideas about the nature of dark energy. They generally predict that it should change its form as the universe expands," says University of Toronto's Ray Carlberg. "(A)s far as we can see, it doesn't."

Carlberg is a member of the Supernova Legacy Survey (SNLS), a collaborative international effort that uses the 3.6-meter Canada-France-Hawaii Telescope atop Mauna Kea, Hawaii, and its giant MegaCam imager. Researchers first identify distant supernovae in MegaCam images then acquire the exploding stars' spectra using some of the largest telescopes on Earth, including the Gemini North and Keck telescopes on Mauna Kea.

Since 1998, astronomers have used distant supernovae to study how cosmic expansion accelerates. They discovered that supernovae at a given distance seem to be fainter than they would be if the universe's expansion were slowing down. This result, which has been observed consistently for the last 8 years, strongly implies that the cosmos is expanding at an ever-faster rate. Astronomers refer to the force driving this apparent increase as dark energy.

<http://www.astronomy.com/asy/default.aspx?c=a&id=3721>
(more at link above)

[Geoff R. Casavant]

1. My best guess

1. Astronomers can accurately measure a given star's distance by measuring the red shift in its spectral lines, since red shift is a function of speed of recession, which is a function of distance. I think they make an assumption that stars are pretty similar across the universe, so that far stars of a particular composition are similar to near stars of similar composition.

2. Since we can determine the absolute brightness of nearby stars, we can assume that far stars have the same absolute brightness. Based on the knowledge of absolute brightness and distance, the expected perceived brightness may be calculated. Then we can note that the actual perceived brightness is less than the calculated perceived brightness.

[Ian David]

4. Someone is building Dyson Spheres around the stars.

And using the power thus harvested billions of lightyears away to make crop circles right here on Earth.

[Straight Shooter]

6. Excellent summary in two paragraphs. I am impressed.

One thing which could change the perceived versus calculated brightness is a yet unknown factor at play in the universe. It seems we are constantly surprised by how much we do not know in the realms which lurk beyond our ability to investigate and verify.

Thank you for that explanation. Science is most interesting when it is explained most simply.

:thumbsup:

[Up2Late]

7. That sounds like a damn good guess, thanks.

Here's another fact for those of you who don't give much thought to Astronomy might want to ponder:

Our Sun is thought to be a very "average" star. Now, if I remember correctly, the estimated lifespan of our Sun is about 12 Billion years.

So, if we are able to see stars that are more than 6 to 12 Billion light years away now, most of those stars at that distance that we see have, most likely, already exploded, or turned into Red Giants, or White Dwarfs, or even Black Holes. BUT, by the time the light showing that explosion arrives at Earth, most likely our star and planets will be long gone too (due to the death of our Sun).

[acmavm]

2. This stuff is just amazing and fascinating. And although I can only grasp

some of this stuff in its crudest most simplistic explanations, I'm still fascinated. Guys like Ed Whitten and his 'theory of everything' freak me out. How does their mind work? What do they think about for entertainment and fun? How do they come up with this stuff. 126 different dimensions and the universe like a loaf of sliced bread? Amazing.

And Einstein. To be so far out ahead of everyone else. Like Isaac Newton was. How does it feel to be so right and so misunderstood?

[cdeca2005]

3. Flying Spaghetti Monster is the only Truth. NT

Flying Spaghetti Monster is the only Truth.

[Ian David]

5. The most fascinating physics fact I've learned in years...

Gravity travels at the speed of light.

[icymist]

9. Where did you get that from?

I have found the quote "gravity is not a force but a curvature in space-time" ~A. Einstein, 1916 I would speculate that gravity travels, not only at the speed of light, but varies with the mass of the object causing the abnormality within the space-time.

[bemildred]

11. The Speed of Gravity - What the Experiments Say

Enjoy.

Abstract

Standard experimental techniques exist to determine the propagation speed of forces. When we apply these techniques to gravity, they all yield propagation speeds too great to measure, substantially faster than lightspeed. This is because gravity, in contrast to light, has no detectable aberration or propagation delay for its action, even for cases (such as binary pulsars) where sources of gravity accelerate significantly during the light time from source to target By contrast, the finite propagation speed of light causes radiation pressure forces to have a non-radial component causing orbits to decay (the "Poynting-Robertson effect"); but gravity has no counterpart force proportional to v/c to first order. General relativity (GR) explains these features by suggesting that gravitation (unlike electromagnetic forces) is a pure geometric effect of curved space-time, not a force of nature that propagates. Gravitational radiation, which surely does propagate at lightspeed but is a fifth order effect in v/c, is too small to play a role in explaining this difference in behavior between gravity and ordinary forces of nature. Problems with the causality principle also exist for GR in this connection, such as explaining how the external fields between binary black holes manage to continually update without benefit of communication with the masses hidden behind event horizons. These causality problems would be solved without any change to the mathematical formalism of GR, but only to its interpretation, if gravity is once again taken to be a propagating force of nature in flat spacetime with the propagation speed indicated by observational evidence and experiments: not less than 2 x 1010 c. Such a change of perspective requires no change in the assumed character of gravitational radiation or its lightspeed propagation. Although faster-than-light force propagation speeds do violate Einstein special relativity (SR), they are in accord with Lorentzian relativity, which has never been experimentally distinguished from SR-at least, not if favor of SR. Indeed, far from upsetting much of current physics, the main changes induced by this new perspective are beneficial to areas where physics has been struggling, such as explaining experimental evidence for non-locality in quantum physics, the dark matter issue in cosmology, and the possible unification of forces. Recognition of a faster-than-lightspeed propagation of gravity, as indicated by all existing experimental evidence, may be the key to taking conventional physics to the next plateau.

http://www.ldolphin.org/vanFlandern/gravityspeed.html

[Ian David]

12. A more recent and accepted theory contradicts that- Gravity travels at C

Gravity Moves at the Speed of Light

Summary - (Jan 9, 2003) Theorized by Einstein for almost a century, physicists have found evidence to support the theory that the force of gravity moves at the speed of light. The speed was measured by physicist Sergei Kopeikin by watching how light from a distant quasar was bent by Jupiter's gravity. Variations in how the image of the quasar was bent accounted for this speed of gravity.

Full Story -

Taking advantage of a rare cosmic alignment, scientists have made the first measurement of the speed at which the force of gravity propagates, giving a numerical value to one of the last unmeasured fundamental constants of physics.

"Newton thought that gravity's force was instantaneous. Einstein assumed that it moved at the speed of light, but until now, no one had measured it," said Sergei Kopeikin, a physicist at the University of Missouri-Columbia.

"We have determined that gravity's propagation speed is equal to the speed of light within an accuracy of 20 percent," said Ed Fomalont, an astronomer at the National Radio Astronomy Observatory (NRAO) in Charlottesville, VA. The scientists presented their findings to the American Astronomical Society's meeting in Seattle, WA.

More:
http://www.universetoday.com/am/publish/speed_of_gravity.html?912003

[bemildred]

13. Yeah, that's what Brian Greene said in "The Elegant Universe" too, IIRC.

I remember reading about the quasar measurement you posted.

I ran into another piece somewhere recently (can't remember) that expatiated in some detail on the fact that the Michelson-Morley experiments did not in fact support SR, but showed a "descrepancy".

[Ian David]

14. Here's what I think is a good analogy...

Place a glass of wine at one end of a trampoline.

Dress-up like the planet Jupiter and run across the other end of the trampoline.

See how long it takes for the glass of wine at the other end to spill as you run across the trampoline.

Even if gravity is a deformation of a membrane, it still takes time for the shock-waves or "stretches" to reach it.

Apparently the same thing applies to a long rope.

If you have a rope that's one light-year long, and you pull on one end, it will still take at least one year for the person holding the other end of the rope to feel it. Even if that rope is made out of space-time.

[bemildred]

16. LOL.

Yeah, that's what Greene said too, more or less, ripples in space time.

Which makes sense to me too. The foundations of SR seem unimpeachable to me, the underlying reasoning that there are no special frames. I found Greene's explanation very accessible, too. I take it as evident that the universe is "consistent", but I enjoy some of these debates over how it works, and it's a lot of work to really sort things out for yourself.

Greene also says in one chapter that everything is always moving at the speed of light, and the apparent differences in velocity that we observe result from variations in the constant magnitude velocity vector's projection onto the 3 spatial and one time dimension. Hence the faster your relative velocity in space, the slower your observed passage through time.

[Up2Late]

17. Your "long rope" is a good analogy, but the theory that...

"...gravity is a deformation of a membrane..." is total BS, who ever came up with that one was breathing in too much chalk dust.

When I saw Brian Greene talking about that on his PBS version of "The Elegant Universe" I almost jumped out of my chair. I'd love to set him straight on that one. I'd also like to explain my "Dark Matter" theory to him too.

Plus, I think I might have thought up a way to demonstrate a "real world" example of String Theory too, not sure if I could come up with a scintific way to prove it though, that's the really difficult part.

Another analogy, similar to your "rope" example would be, If you were able to shoot a powerful laser, in the vacuum of space, at a target that is 1 light year away, for 1 year.

If you could instantly see what the target (which is 1 light year away) sees, it would take 2 years, between the moment you fired (turned on) the laser and the time you see the laser turn off again.

[Up2Late]

18. Ow! Reading that made my brain hurt!

I know that's how it was presented at it's website, but next time, try to break it up into smaller paragraphs. Big, single spaced paragraphs like that, are murder to read, especially off a computer screen.

[Vinnie From Indy]

8. I think your question might could be answered thusly

If the universe were indeed "closed" (expansion eventaully stops and reverses to a "big crunch") rather than "open" (universe expands forever) then the faintest stars should not be as far away as this new data suggests that they are.

[icymist]

10. From Scientific America web site:

Supernovae Back Einstein's "Blunder"

When Albert Einstein was working on his equations for the theory of general relativity, he threw in a cosmological constant to bring the universe into harmonious equilibrium. But subsequent observations by Edwin Hubble proved that the universe was not static. Rather, galaxies were flying apart at varying speeds. Einstein abandoned the concept, calling it the biggest blunder of his life's work.

Observations in the 1990s, however, proved that the universe was not only flying apart, it was doing so faster and faster. This seemed to point to a dark energy filling space that actually repelled ordinary matter with its gravity, in contrast to all other known stuff, including dark matter. A number of theories have been developed to explain what this dark energy might be, including Einstein's long discarded cosmological constant.

(More)
http://www.sciam.com/article.cfm?chanID=sa003&articleID=00023144-9B65-1383-9A5083414B7FFE87


I find it awesome that Einstein was off in his calucation by a mere -.15!

[Ian David]

15. Maybe "Dark Energy" can explain the discrepancies in the Ohio vote...

It was causing voter intent to separate itself at an accelerating rate from voting results.