Method to Test String Theory Proposed

Article written: 29 Jan , 2008
Updated: 26 Dec , 2015

What is the universe made of? While general relativity does a good job providing insights into the Big Bang and the evolution of stars, galaxies and black holes, the theory doesn’t help much when it gets down to the small stuff. There are several theories about the basic, fundamental building blocks of all that exists. Some quantum physicists propose string theory as a theory of “everything,” that at the elemental heart of all matter lie tiny one-dimensional filaments called strings. Unfortunately, however, according to the theory, strings should be about a millionth of a billionth of a billionth of a billionth of a centimeter in length. Strings are way too small to see with current particle physics technology, so string theorists will have to come up with more clever methods to test the theory than just looking for the strings.

Well, one cosmologist has an idea. And it’s a really big idea.

Benjamin Wandelt, a professor of physics and astronomy at the University of Illinois says that ancient light from the beginnings of our universe was absorbed by neutral hydrogen atoms. By studying these atoms, certain predictions of string theory could be tested. Making the measurements, however, would require a gigantic array of radio telescopes to be built on Earth, in space or on the moon. And it would be really gigantic: Wandelt proposes 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.

So for now, both string theory and this method of testing are purely hypothetical.

According to Wandelt, what this huge array would be looking for are absorption features in the 21-centimeter spectrum of neutral hydrogen atoms.

“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 Wandelt. “If we embed brane inflation into string theory, a network of cosmic strings is predicted to form. 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.”

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. Wandelt compared their composition 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. String theory predicts that a network of strings were produced in the early universe, but this has not been detected so far. Cosmic strings produce fluctuations in the gas density through which they move, a signature of which Wandelt says will be imprinted on 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.

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.”

But questions remain about the validity of this experiment. Also, could the array somehow be “shrunk” to search only a small area of the 21-centimeter radiation? Or possibily, could an instrument similar to WMAP (Wilkinson Microwave Anisotropy Probe) be constructed to look at the entire sky for this radiation?

Wandelt and graduate student Rishi Khatri describe their proposed test in a paper accepted for publication in the journal Physical Review Letters, and the paper is not yet available for public review.

Original News Source: University of Illinois Press Release


31 Responses

  1. The telescope could be built by positioning a satellite at geostationary orbit above a crater of sufficient size on the equator Mars. Craters there are of all different sizes and focal lengths, and one of them is bound to focus energy to a height of a geostationary satellites. Mars has the orbital period and the gravity that this would work. They should send a satellite to that place or a constellation of satellites.

  2. With all the ice in the Martian dirt, it would be optimal for reflecting the hydrogen wavelength.

  3. Detonating a nuclear bomb at the right debth below the surface of the ice covered asteroid Ceres might also be a good way to build a satellite dish of the right size. With no moons or other bodies to perturb the orbit of the antenna satellite, there is less chance that the system would not be stable, even if geostationary satellite orbit is very distant from the asteroid. Of course, it’s low gravity would make geostationary orbit close anyway.

  4. String theory certainly likes to live large. Even the proposed test is so hard to achieve that it might not be practical for many years.

  5. Ron Evans says

    Could a very long base-line interferometer (Earth to Moon or some other similarly long base-line) do the same job without the 1000 square km area?

  6. Jason Leary says

    Thought that subatomic strings and cosmic screens are separate entities ? So what bearing would cosmic strings have on the topic of sub-atomic strings ? Sounds like some equivocation is going on .

  7. shinnok says

    I think he meant that subatomic strings are thought to make up the very fabric pf space time, as opposed to the cosmic stings that have been stretched to infinite lengths by cosmic expansion…..

  8. Johnny Blues says

    Hmm, the most amazing and utterly confusing prediction in String Theory hasn’t been mentioned at all, multiple universes coexisting. The article mentions “brane” which is also how some describe the separation between these theoretical universes.

    Maybe we should look for types of energy that just disappear, defying our laws of physics, unless it passes thru a brane to an alternate universe. What is NOT there gives as much information as what IS there.

    But man o man, String Theory is so hard to wrap your head around. I wonder if we will ever understand it fully.

  9. There never was a Big Bang. There are no “Branes”. It is impossible to create a singularity.

  10. Johnny Blues says

    I’m not even going to address disbelief in Big Bang, dark matter, dark energy and singularities.

    But, we may be very close to having proof of them. Yes, not blackboard proof, actual and physical proof that can be recorded and studied. The Hadron Collider could create micro-black holes and prove the existence of other dimensions. More details at

  11. Tom says

    Wow…short and to the point, huh? No Big Bang? I admit, it is difficult to get your arms around some of the more extreme aspects of our current “theories of everything”, string theory being no different…but while we cannot get to the very beginning of time we have been able to get extremely close to it.

    At last count I understood that we were had solved back to just seconds or fractions of a second prior to the big bang, in a brief time period where the accepted laws of physics did not yet apply (prior to the point where the strong and weak nuclear forces and the electro-mag force split, and just after time had begun).

    There are theories, equations, observations, and universe-wide background radiation and heat left over from the event that, while not conclusively proving the theory, offers plenty of evidence to support it.

    What data do you have to back up your statements that these things never existed?

    Being men & women of science we are always ready to hear other’s supporting and dissenting theories, providing you can back it up…

  12. W. Scott says

    Mister Coles, saying there was no Big Bang is tantamount to saying that the moon is made of cheese. We already have ample science on this.

    When we talk about String theory, it’s important to remember that several different and independent String Theories were developed, all of them mathematically sound, which for theorists was a problem. An equation cannot have two or more contradictory right answers. M-Theory is the intersection of String Theory and Supergravity, and it is M-Theory which describes membranes as fundamental to multidimensional cosmology.

    The proposed experiment would probably shed light on the subject, and the array could also be used for other astronomy. But the economics of creating something so massive and so immaculately precise are ridiculously prohibitive, considering that it still couldn’t “prove” the theory, only provide supporting evidence… or it could disprove the theory by providing contradictory evidence. But until we have demonstrable and practical need to validate String Theory, such an experiment could not be adequately funded. Scientific discovery most often rides on the shoulders of practical applications. Perhaps it shouldn’t be that way, but that’s the way it is.
    So far, M-theory (which includes String Theory) is consistent with all the experimental data we have. It would be far more cost effective to fund more theoretical research in hopes of making predictions that would be more economical to experiment with.

  13. Alex says

    This would be a good reason to spray a crater on the far side of the moon with aluminum or something along those lines. Experiments like that dont cost money – they make money. : )

  14. Truey says

    First of all comparing the big bang thoery to the certainty that the moon is not made out of cheese is an interesting way of beginning to respond to someone who is not convinced the BB theory is correct.

    There is a reason for the word theory and a definition as well. I personally don’t think its true either only because it deals with the entire universe which is so incredibly vast and constantly being rediscovered.

    I think the current theories, which may be correct and somewhat accurate, rely on too many assumptions such as dark energy, dark matter, and the so called singularity.

    I’m not trying to discredit anyone or anything, just saying that science is certainly going in the only direction it can go based on what is possible for us to measure. However don’t make theories like the big bang or anything else for that matter become a scientific dogma. That in itself is not science.

  15. Dwight says

    Amazing. These psycho-bably scientists always come up with ways to “test” things that involve gigantic expenditures with no doubt plenty of well paying jobs for graduate students, various “PhDs”, Senior Investigators, Principle Investigators, Project Leads, and even just normal scientists. Sorry folks, we can’t afford your breakthroughs.

  16. Pope Priorius X says

    Pray for salvation, Dwight. If you don’t understand why you must kneel at the altar of string theory, it is because you are neither called, chosen nor intellectually capable of understanding.

    Science was once a realm where observation and experimentation was the path to understanding the universe around us. That’s a cute way of practicing science but the followers of string theory have evolved beyond such childlike exploration.

    Compared to the leading proponents of string theory, all “old DNA” scientists from Newton to Sagan were tragically retarded. Without the “new DNA”, you are what Watson & Crick might refer to as “one of the mud people.”

    Watson & Crick were the missing links between old and new DNA. They were simultaneously retarde (profoundly in many cases) yet showed flashes of the “new DNA” string theorists you ignorantly mock.

    Bow your head.

  17. triuneconcept says

    Big Bang makes no sense unless you invoke the theory of inflation to explain the dimensions of the known universe (horizon and flatness problem). But that assumption violates the law of physics regarding the maximum value for the speed of light even though it was for a brief time. As a unbiased scientist, I must then reject the Big Bang theory even though I may want to accept it. If the laws of physics are violated once, then they can be violated more than once. It is always good to question theory that doesn’t make complete sense. That is why, for example, Einstein questioned Newton. Thinking out of the box is always a good scientific approach. By the way, Smolin’s latest book, “The Trouble with Physics” questions the validity of string theory. I hope you then do not conclude that Smolin thinks the moon is made of blue cheese!

  18. Sci-Fu Black Belt says

    The cheese theory was proven false decades ago.

    The moon is a giant ball of aluminum foil.

    Everybody knows that.

  19. Dwight says

    Poor me, I’m just an amateur physicist/cosomologist and likely won’t add anything to the scientific discussion. Anyway, what with strings, superstrings, branes, and branes consisting of branes, and who knows what else you folks dream up but can’t empricially demonstrate, I’d like to see something like the “X Prize” for physics, say something like $10M for the first researcher to prove the existence of even one additional dimension. Remember, math on a blackboard doesn’t. count… need something tangible.

  20. R. Walsh says

    It certainly sounds like a good idea.
    A system of smaller antenna in phase array would work as well or perhaps as good as a large one.

    I was always under the impression had any advances were to made here, it would probably within gravitation.

    However, this sound interesting….

  21. mostef says

    The speed of light “speed limit” applies only to matter, radiation, and gravity. It does not apply to the fabric of space! Therefore there is nothing inconsistant or irrational about the theory of inflation.

  22. Brian says

    In reference to the suggestions of building a dish to look for strings, or nuking one of our own on a moon, why not use several smaller satellites in a network? Position several in a geostationary orbit around the sun (at a distance of, say, 1 AU). Wouldn’t this give us the equivalent of a 2 AU diameter dish?

    As for the Big Bang, saying that it didn’t happen isn’t correct. As mentioned by Tom, we have evidence that at the very least supports the theory. We can possibly get a few fractions closer, but I don’t see us actually seeing what happened at the exact moment the BB occurred (ie: dividing a positive number in two will never get you zero).

  23. triuneconcept says

    But Mostef, if the speed of light limit does not apply to the fabric of space, how did the matter, radiation, and gravity get to the same place dimensionally as the fabric of space did at the same time? Does the fabric of space have a speed limit? Can the fabric of space now decrease at any time at the same rate as it did in the beginning when it increased?

  24. Ashish says

    I tend to agree with Mr Coles that BB might not have happened. My personal view is
    that the Gravitational Blue and Red Shifts might have some other scientific explanations,which just might throw the BB out of the window.

  25. Jason Leary says

    Hello Mr.Shinok ,
    could be that he meant that in regard to cosmic strings .

  26. Jason Leary says

    To those who do not believe in the Big Bang :

    Truey , haved you read the dictionary definition of theory ? (Since you invoke the definition, thought to ask) .

    One person claimed that the faster than light expansion involved in reflection would violate physics by the fabric of space being said to go past the speed of light .

    Well several conisderations are in order .

    For one , physicists working with cesium gas got light itself to go a little bit past its normal speed of 186, 000 miles per second —according to one science article I read a number of years ago .

    Secondly if the fabric of normal space expanded it would have had to expand into some other *type* of space —with somewhat different toplogical qualities . I know that there are those who could say otherwise—that it didn’t have to have something to expand into (but that claim to the contrary would be mystification and incoherent) .

    Recursively you cannot have an inside without an outside –since the very concept inside exists in contradistinction to an outside .

    What does that last argument have to do with whether space could have expanded at beyond the usual speed of light at 186, 000 miles per second (you may ask) ?

    Well if there was a topologically different type of space that the space of the original Big Bang inflation expanded into —expansion into it might have somewhat different physical constants that the extant sort of cosmic environs in which we reside now .

  27. Jason Leary says


    The idea of an expanded universe is the cosmology that one of the books of the Bible teaches. Isaiah 42: 5 describes God as ‘he that created the heavens and stretched them out …..’

  28. mostef says

    Triuneconcept, In 1905, Einstein postulated only the yardsticks of time measurement (ie. matter and radiation) cannot travel faster than the speed of light. Another way to look at it is to consider the current expansion of the universe. It appears that distant galaxies are receding near the speed of light when in fact they are moving no faster than our galexy moves relative to our nearby clusters of galexies. The distant galexies have a significant red shift not because they are moving faster than us but because the intervening space is expanding.

  29. triuneconcept says

    Mostef, why could not the red shift be due to the galaxies only changing direction but not velocity relative to our frame of reference? As we know, acceleration can be either a change in direction and/or a change in velocity.

  30. RUF says

    Don’t sell yerself short by saying you are “just an ametuer.” You hit the nail right on the head — always dreaming up ideas that can’t be empricially demonstrated is not science — it is philosophy.

  31. Steven Turner says

    I don’t know where to start, but I need to start somewhere, thus would you take the time to read this? My name is Steven Turner, and I am a physicist in my own right. I started writing about psychology when I was thirteen years old and continued until I was twenty-two. I had not had a teacher of this, so I did all my examinations alone. When I was about twenty-three, my mind began changing focus towards the way our universe works. Again having no teacher, I had to figure it out alone. I wanted to determine how our atom works. I began testing personal theories about simple mathematical codes that the universe could use. Instead of trying to actually see what was going on in an atom, I tried to establish the only possible code that an atom could operate with. This seemed easier for I had no access to a collider, which I had no idea even existed at the time. I spent roughly three years figuring out a code that worked easily, simply, and well. Once I got this done, I signed up for a few classes at a college in order to slightly test my theories. I took a simple algebra class and a psychology class. I tried to show the math teacher some of my work, but not only did he seem to look at me as lesser than him, but he also seemed completely uninterested with my years of work. I suppose I really cant expect more from a teacher that’s just wants to teach his class, and pass no judgment, but I attained multitudes of universal information during attendance of the class. During my psychology class, it was as if I were at home, seeing things I had never noticed before. Within a few classes I noticed that the makeup of the mind was tightly comparable to the composure of the atom. I began connecting the known knowledge of psychology, with my theories of what I now call atomics, or universal mathematics. Soon I had begun creating something I would like to introduce to the world of science, as ((Psychological Atomics)). I believe I can explain how our minds follow the exact nature of atomic signatures, signals, transfers, disturbances, equations, and much more. I may not be a professional in the eyes of acknowledged world scientists, but I do have a great deal of heart for this. I believe that the universe is so simple that it may be easy to decipher its mechanisms by comparing everything we see around us. Mathematics is universal and associates with every natural world existence. Instead of just breaking the atom down I went straight for what I like to call the ((Bottom)). After briefly reading into some reports, I found that many call the bottom, the ((God particle)). I am trying to crack the atom code in a mobile home, within a small town of Arizona. I CAN DO IT!! All I need is a little time with professionals that I don’t know how to get in touch with. I have put atomics into algebraic and geometric formats and although I don’t have this code complete, I think I am closer than I should be. I can easily explain why light travels faster than sound, and why we don’t age while traveling at the speed of light. Time measurement is easy to define and calculate with this theory. I can make it complex enough to evade many, or easy enough for a grade school student to understand. I have over five hundred pages of journalism and diagrams to share with the scientific world, and whether or not it can ever be taken seriously, I would like to share it with someone. I am also timid to share it, in possibility that it will be stolen, but we all deserve and share the same knowledge together do we not? It doesn’t matter who figures these things out, it only matters that we do. I believe that I have a good idea of what happened seven steps before the Big Bang. This is all I am comfortable sharing at this point.

    Thank you,
    Your fellow physicist
    [email protected]

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