Scientists propose test of string theory based on neutral hydrogen absorption

January 28, 2008

Ancient light absorbed by neutral hydrogen atoms could be used to test certain predictions of string theory, say cosmologists at the University of Illinois. Making the measurements, however, would require a gigantic array of radio telescopes to be built on Earth, in space or on the moon.

Ancient light absorbed by neutral hydrogen atoms could be used to test certain predictions of string theory, say cosmologists at the University of Illinois. Making the measurements, however, would require a gigantic array of radio telescopes to be built on Earth, in space or on the moon.

String theory – a theory whose fundamental building blocks are tiny one-dimensional filaments called strings – is the leading contender for a “theory of everything.” Such a theory would unify all four fundamental forces of nature (the strong and weak nuclear forces, electromagnetism, and gravity). But finding ways to test string theory has been difficult.

Now, cosmologists at the U. of I. say absorption features in the 21-centimeter spectrum of neutral hydrogen atoms could be used for such a test.

“High-redshift, 21-centimeter observations provide a rare observational window in which to test string theory, constrain its parameters and show whether or not it makes sense to embed a type of inflation – called brane inflation – into string theory,” said Benjamin Wandelt, a professor of physics and of astronomy at the U. of I.

“If we embed brane inflation into string theory, a network of cosmic strings is predicted to form,” Wandelt said. “We can test this prediction by looking for the impact this cosmic string network would have on the density of neutral hydrogen in the universe.”

Wandelt and graduate student Rishi Khatri describe their proposed test in a paper accepted for publication in the journal Physical Review Letters.

About 400,000 years after the Big Bang, the universe consisted of a thick shell of neutral hydrogen atoms (each composed of a single proton orbited by a single electron) illuminated by what became known as the cosmic microwave background.

Because neutral hydrogen atoms readily absorb electromagnetic radiation with a wavelength of 21 centimeters, the cosmic microwave background carries a signature of density perturbations in the hydrogen shell, which should be observable today, Wandelt said.

Cosmic strings are filaments of infinite length. Their composition can be loosely compared to the boundaries of ice crystals in frozen water.

When water in a bowl begins to freeze, ice crystals will grow at different points in the bowl, with random orientations. When the ice crystals meet, they usually will not be aligned to one another. The boundary between two such misaligned crystals is called a discontinuity or a defect.

Cosmic strings are defects in space. A network of strings is predicted by string theory (and also by other supersymmetric theories known as Grand Unified Theories, which aspire to unify all known forces of nature except gravity) to have been produced in the early universe, but has not been detected so far. Cosmic strings produce characteristic fluctuations in the gas density through which they move, a signature of which will be imprinted on the 21-centimeter radiation.

The cosmic string network predicted to occur with brane inflation could be tested by looking for the corresponding fluctuations in the 21-centimeter radiation.

Like the cosmic microwave background, the cosmological 21-centimeter radiation has been stretched as the universe has expanded. Today, this relic radiation has a wavelength closer to 21 meters, putting it in the long-wavelength radio portion of the electromagnetic spectrum.

To precisely measure perturbations in the spectra would require an array of radio telescopes with a collective area of more than 1,000 square kilometers. Such an array could be built using current technology, Wandelt said, but would be prohibitively expensive.

If such an enormous array were eventually constructed, measurements of perturbations in the density of neutral hydrogen atoms could also reveal the value of string tension, a fundamental parameter in string theory, Wandelt said. “And that would tell us about the energy scale at which quantum gravity begins to become important.”

Source: University of Illinois at Urbana-Champaign

Explore further: Best of Last Week – Testing for extra dimensions, solving the riddle of life on Earth and fatty acids that slow cancer

Related Stories

Scientists find a practical test for string theory

January 6, 2014

(Phys.org) —Scientists at Towson University in Towson, Maryland, have identified a practical, yet overlooked, test of string theory based on the motions of planets, moons and asteroids, reminiscent of Galileo's famed test ...

Searching for defects in space

December 19, 2012

Topological defects in space may have developed fractions of a second after the Big Bang. Simulations of these wormlike entities and a comparison of the simulations with cosmic background radiation measurements by the Planck ...

Listening to the stars

December 1, 2011

It is almost night on the island of Puerto Rico. Astronomer Joanna Rankin raises her head toward the sky. A few of the brightest stars shine through blue cracks in a ragged dome of gray clouds. To her back, a jungle throbs ...

Recommended for you

Short wavelength plasmons observed in nanotubes

July 28, 2015

The term "plasmons" might sound like something from the soon-to-be-released new Star Wars movie, but the effects of plasmons have been known about for centuries. Plasmons are collective oscillations of conduction electrons ...

'Expansion entropy': A new litmus test for chaos?

July 28, 2015

Can the flap of a butterfly's wings in Brazil set off a tornado in Texas? This intriguing hypothetical scenario, commonly called "the butterfly effect," has come to embody the popular conception of a chaotic system, in which ...

Lobster-Eye imager detects soft X-ray emissions

July 28, 2015

Solar winds are known for powering dangerous space weather events near Earth, which, in turn, endangers space assets. So a large interdisciplinary group of researchers, led by the U.S. National Aeronautics and Space Administration ...

3 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

earls
not rated yet Jan 28, 2008
Great idea, minus the "prohibitively expensive" part. :(
Ashibayai
not rated yet Jan 28, 2008
Yeah, this is definitely something that will be a ways off if we don't find a better way to collect data in the mean time.

Maybe we'll hit a roadblock in our learning after projects like LHC give out all the information they can provide us, and we'll consider building something like this.
NanoStuff
not rated yet Feb 03, 2008
Judging by the cost of SKA, this would be at least a Trillion dollar project.

I'll donate 20 dollars if you two donate 20 dollars.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.