Is There a 'Fifth Force' that Alters Gravity at Cosmic Scales?
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May 11, 2012

Is There a 'Fifth Force' that Alters Gravity at Cosmic Scales?



Radical new research is attempting to characterize the properties of a fifth force that disrupts the predictions general relativity makes outside our own galaxy, on cosmic-length scales. University of Pennsylvania astrophysicist Bhuvnesh Jain, says the nature of gravity is the question of a lifetime. As scientists have been able to see farther and deeper into the universe, the laws of gravity have been revealed to be under the influence of an unexplained force.

By innovatively analyzing a well-studied class of stars in nearby galaxies, Jain and his colleagues — Vinu Vikram, Anna Cabre and Joseph Clampitt at Penn and Jeremy Sakstein at the University of Cambridge — have produced new findings that narrow down the possibilities of what this force could be. Their findings, published on the Arxiv (see below), are a vindication of Einstein’s theory of gravity.

Having survived a century of tests in the solar system, it has passed this new test in galaxies beyond our own as well.In 1998, astrophysicists made an observation that turned gravity on its ear: the universe’s rate of expansion is speeding up. If gravity acts the same everywhere, stars and galaxies propelled outward by the Big Bang should continuously slow down, like objects thrown from an explosion do here on Earth.

This observation used distant supernovae to show that the expansion of the universe was speeding up rather than slowing down. This indicated that something was missing from physicists’ understanding of how the universe responds to gravity, which is described by Einstein’s theory of general relativity.

Two branches of theories have sprung up, each trying to fill its gaps in a different way. One branch — dark energy — suggests that the vacuum of space has an energy associated with it and that energy causes the observed acceleration. The other falls under the umbrella of “scalar-tensor” gravity theories, which effectively posits a fifth force (beyond gravity, electromagnetism and the strong and weak nuclear forces) that alters gravity on cosmologically large scales.

“These two possibilities are both radical in their own way,” Jain said. “One is saying that general relativity is correct, but we have this strange new form of energy. The other is saying we don't have a new form of energy, but gravity is not described by general relativity everywhere.”

Jain’s research is focused on the latter possibility; he is attempting to characterize the properties of this fifth force that disrupts the predictions general relativity makes outside our own galaxy, on cosmic length scales.

Jain’s recent breakthrough came about when he and his colleagues realized they could use the troves of data on a special property of a common type of star as an exquisite test of gravity.

Astrophysicists have been pursuing tests of gravity in the cosmos for many years, but conventional tests require data on millions of galaxies. Future observations are expected to provide such enormous datasets in the coming data. But Jain and his colleagues were able to bypass the conventional approach.

“We’ve been able to perform a powerful test using just 25 nearby galaxies that is more than a hundred times more stringent than standard cosmological tests,” Jain said.The nearby galaxies are important because they contain stars called cepheids that are bright enough to be seen individually. Moreover, cepheids have been used for decades as a kind of interstellar yardstick because their brightness oscillates in a precise and predictable way.

“You can measure the brightness of a light bulb at some distance and know that, if you move it twice as far, it will be four times as faint. So you can tell just by the difference in its observed brightness how much further you moved it,” Jain said. “But you need to know how intrinsically bright the bulb is first to determine its actual distance from us.”

Cepheids have a unique trait that allows astrophysicists to get this critical information: their luminosity oscillates over the course of days and weeks. The known relationship between a cepheid’s rate of oscillation and intrinsic brightness serves as that baseline for calculating its distance from Earth, which in turn serves as a baseline for calculating the distance of other celestial objects.

The accelerating universe observation, for example, relied upon cepheid data for scale.“Now that we understand a little bit more about what makes the cepheids pulsate — a balance of gravity and pressure — we can use them to learn about gravity, not just distance,” Jain said. “If the fifth force enhances gravity even a little bit, it will make them pulsate faster.”

Because of their usefulness, there was already more than a decade of data on cepheids based on the Hubble Space Telescope and other large telescopes in Chile and Hawaii. Using that data, Jain and his colleagues compared nearly a thousand stars in 25 galaxies. This allowed them to make comparisons between galaxies that are theoretically “screened” or protected from the effects of the hypothetical fifth force and those that are not. Larger galaxies and ones that belong to galaxy clusters are screened, while smaller, isolated galaxies are not.

“If we compare galaxies that don't permit this extra force, like our own galaxy, with others that do, then we should see a difference in the way those galaxies’ cepheids behave,” Jain said. “Because this new force would increase the speed of their oscillations and because we can use the rate of their oscillations to their measure distance from us, the measurement we get from cepheids in unscreened galaxies should be smaller than distance measurements made with different techniques.”

Jain and his colleagues ultimately did not see variation between their control sample of screened galaxies and their test sample of unscreened ones. Their results line up exactly with the prediction of Einstein’s general relativity. This means that the potential range and strength of the fifth force is severely constrained.

“We find consistency with Einstein’s theory of gravity and we sharply narrow the space available to these other theories. Many of these theories are now ruled out by the data,” Jain said.With better data on nearby galaxies in the coming years, Jain expects that an entire class of gravity theories could essentially be eliminated. But there remains the exciting possibility that better data may reveal small deviations from Einstein’s gravity, one of the most famous scientific theories of all time.

The image at the top of the page shows the most distant X-ray cluster of galaxies yet found by astronomers using NASA's Chandra X-ray Observatory. Approximately 10 billion light years from Earth, the cluster 3C294 is 40 percent farther than the next most distant X-ray galaxy cluster previously known. The existence of such a distant galaxy cluster is important for understanding how the Universe evolved.

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Everything is Energy.
Gravity is just a way to represent that Energy with one of our senses.

I think whatever they try it will finally leads to Energy. :E

Findings show that there are 90% more infrared galaxies that are too faint to detect in all dark energy maps, that all used alpha lyman hydrogen. The phony dark energy scientists never admit they are only showing us about 10% of the total numbers of galaxies. I would obviously expect such a small 10% sample of galaxies to be moving apart from each other faster than the entire 100% does that they never see.

I thought that UPENN had better things to spend their time and money on than attempting to inventing a whole new force for a process that still isn't fully understood. When new evidence is coming to light all the time, bits of the "missing mass" being discovered i.e. the luminosity of distant galaxies can't be used as a measure of their overall mass, galaxies missed by incomplete surveys, and the definitive discovery that the "standard candle" type 1a super novae are actually formed by different processes. Doesn't seem very scientific to me. Eistein definitely wouldn't like this kind of physics!

> I thought that UPENN

The problem is that the 'monkeys' brain is not big nor fine enough, and his technology is severely limited to resolve some of these problems, right away. To answer some of this questions, they invented religion long time ago, and it works almost as well :-)

But the 'monkey' does not gracefully admit to that, and thinks that it can be all knowing.

To say something moronic, the universe is big, really big :-)

It looks there is some circular reasoning going on here. The period of the cepheid variable is used to find its absolute brightness, but the change in gravity is suppose to show itself by a change in period. Wouldn't this change how far away the star appears to be?

Also tests on our understanding of basic physics are not a waste of time. It was such tests around 1900 that lead to General and Special Relativity. Also problems with atomic spectrums lead to quantum mechanics and Albert Eistein's Nobel Prize for explaining the photoelectric effect.

The monkey's brain is NEITHER big NOR fine enough, and his grammar is severely limited...

Yes, there is another force besides gravity that influences the behaviour of the universe. It is called the electric force.

We live in an electric universe, in which most of the mass (>99%) in the universe is composed of plasma, the fourth state of matter. There is no need for "dark matter" or "dark energy" or some more mysterious "fifth force" to explain the behaviour observed.

Whenever the "fudge factor" of any theory becomes larger than theory itself (as the Big Bang theory has become), then you know there's something fundamentally wrong with the theory.

If the measurements don't match the theory, then the theory is wrong.

OK Cato, hold out your hand so Ruth can smack it with a ruler!

And again Ruth, its a shame this is what you contribute. Everyone understood what he meant and not all of us are as edjumacated as you seem to feel. Maybe next time you would add some comments about the story, maybe your opinions (about the story), right or wrong, and maybe give people something to make them go "Hmmmmm". And dont let your fear of looking dumb slow you down. (you should see some of the really WHACKY stuff I posted earlier in your name.) OK, kidding about that. Or am I???

I wonder if 'dark energy' will be the 'ether' of our time. We'll have to wait for a 21st century Michelson-Morley experiment.

Gravity's affect is felt at the speed of light. It moves through subspace at the speed of light, therefore the speed of light is a constant in subspace. There are four levels of subspace. the first is a ratio of 111 km of subspace equals only 1 km of distance in our dimension. This ratio is given to us from mythology, Saturn being near the mark, it's name meaning Time, Chronos. Time the light reaches saturn from the sun and it's delt of gravity disturbances from the sun. The pyramids were the the hint of subspace, as above, so below. Why four sides? Four levels. The third ratio is found by using the distance to the star ra, that the orion belt in combination with plaedies points to. Why use the belt of orion and its three stars? It is the third level of subspace hidden in our mythology. The distance from our sun to ra or star hd 283271 is about 15.7 light years. For every km on earth, in subspace level three we travel the equivilent in 15.7 light years of kilometers. 15.7 added 15+7 is 22 or 11/11. eat that mf's.

it fascinates me to see there in an additional force that controls the gravity in the early evolution of the universe. i also thought that things just after Big bang creation of universe may take time to reach steady state. This stage confined to say, within first billion years, may be characterized by change in the magnitude of physical constants and even the strengths of the four force/fields. Gravity is the first field to emerge, in the sequence of strong nuclear, electromagnetic and nuclear weak. Its lack of amiability to unification with other three fields show its special nature of ' variability ' as per the demands of the logic of evolution of the universe following Big Bang anomaly. Nothing physical had given rise to everything in the form of the universe.

Wouldn't it be a lark to discover that the mysterious force influencing gravity at the Cosmic scale is consciousness??

Forces always come in pairs. If there is a 5th force, I am sure there is a 6th force.

Oh my goodness, you guys. These comments. Wow.

Virtual particles, attractive cancel back to photons, and gravity, repulsive take longer to recombine, and express a net repulsion.

SP: Don't let it get to you so much, I think I must be a bit OCD.

To JR, the world doesn't revolve around your wants and needs.

We don't absolutely understand gravity much less how [or how fast] it acts over cosmic distances. Positing a 5th force is a purely intellectual exercise at this stage. Surely it is impossible to verify the continuing existence of galaxies observed at even 'moderate' distances from our own unless it is through their exigent gravitational influences.

Tosca Z: it would be quite the lark indeed, and if you haven't already, you should look into reading "Last and First Men" and "Star Maker" by Olaf Stapledon. Without giving too big a spoiler, Stapledon made the same assumption as you and used it in his novels.

Gravity, Oh, gravity how to understand your true nature.
Just disappear from the world, we shall know what you are!
You keep some as stars and other as planets,
Then you allow galaxies of such communities.
How was it when you were alone,
Why you do not allow your following fields
A chance to become friendly with you!
Scientist say that you also have a quantum aspect,
While earlier days were simple when you just had classical nature!
But then you may say science has got both these aspects,
as one dominates macro and the other micro-world!
What about some world in between say, nanomaterials,
That are neither micro nor macro!
Yes, i eagerly look for some theory that is in between,
and may explain every phenomenon that takes place in cosmos!

Thanks Tosca Z for the Olaf Stapledon references. I will read them.

May I also say that we may never be in a position to prove or disprove a lot of things including the continuing existence of anything outside our immediate cosmic neighbourhood, whether or not the universe is infinite or expanding beyond the speed of light [maybe they're really the same thing in any meaningful sense anyway] or when, how [or how often] and if the universe had a beginning and will ever end.

Let me see if I got this all straight. The universe was created in an explosion in a space smaller than the diameter of an atom out of nothing. For a billionth of a second or so, all of this matter was suddenly speeded up by some unknown force to a speed greater than the speed of light (this explains homogeneity.)When the universe cooled down from the quark soup and formed atoms, the "Dark Force," (which nobody knows its cause) helped form galaxies. And, the expansion of the universe is speeding up, not slowing down, which means that there is some other undiscovered force that is counteracting gravity. The Dark Force and Dark Matter make up 96 percent of the matter in the universe and visual matter (Atoms and energy) make up less than 5 percent. Did I get this right?

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