What do you find in higher dimensions

Time travel through higher dimensions

"No Strings Attached" can sometimes be read on funky T-shirts. That can mean different things: advertising for an a cappella band from Hamburg (which plays pop music without stringed instruments), reminiscence of a festival for extraordinary theater in Mainz - or simply the English idiom for “unconditional”, “without hooks and eyes "," Without further obligations ". Long-time readers of bild der Wissenschaft immediately think of string theory, despite the negative, of course - the hottest candidate for a "world formula" that combines quantum theory and relativity and describes the forces of nature in a uniform way. With the help of string theory, physicists have now shown how certain elementary particles could travel through time. That would not only have truly multidimensional consequences for our worldview. It would also explain strange measurements from neutrino experiments, perhaps solve a cosmological puzzle, and refute a conjecture made by Stephen Hawking.

In order to understand all of this, you have to go back a little - even into the fifth and sixth dimensions. Too difficult? Well, string theory even postulates the existence of six or seven additional dimensions of space. But these are all (or almost all) extremely small and therefore imperceptible. They are, as it were, rolled up - similar to how a garden hose may appear as a one-dimensional line from a great distance, although in reality it is thick. The additional string dimensions are, of course, only 10–32 centimeters in size. This is also the length of the vibrating strings ("strings"), from whose excited states, according to string theory, all elementary particles arise. The world would be, as it were, the concert of these submicroscopic tiny creatures.


In certain scenarios of string theory, there are not only strings but also “D-branes” that are two- or multi-dimensional. This was already being considered in the 1970s - including by Michael Green, who has been Stephen Hawking's successor at Cambridge since November 2009. The "D" honors the German mathematician Johann Peter Gustav Lejeune Dirichlet (1805 to 1859). The open strings are attached to these D-branes - similar to the two ends of a thread that have been glued to a piece of paper (see graphic “Strings and branes”). It is conceivable that D-branes form multidimensional forms of matter or black holes. Perhaps our entire universe is even a huge D-brane in a higher-dimensional space. Everything we know would then consist of vibrating strings attached to this brane.

Everything? Maybe not quite! Because closed strings that are ring-shaped and therefore have no ends would not be limited to the bran. You could escape into the additional space dimensions, the "bulk" (English for "main part"). This would be the case with gravitons, the carrier particles of gravity. At least that's what many string theorists think, who regard gravitons as closed strings.

If the extent of at least one of these extra dimensions were relatively large - a thousandth of a millimeter would be consistent with previous measurements of the gravitational constant - then this hypothesis would have a great advantage: It could explain why gravity is so much weaker - 1032 times weaker ! - as the second weakest force in nature, the weak interaction, which is responsible, among other things, for radioactive beta decay. In contrast to all other forces that are limited to the bran, gravity acts in all dimensions. Because the gravitons escape from the bran - in contrast to the carrier particles of the other forces - and this "dilutes" the force of gravity accordingly.

So if a dashing woman wears “No Strings Attached” on her T-shirt, she will have to be asked whether she is not a D-Bran - and whether at least gravitational interactions with her are allowed. So this article is not only about exotic topics in theoretical physics, but also gives useful tips for hooking up at the next party. But be careful: Perhaps the party girl is very familiar with strings, i.e. with string theory, and quick-wittedly counters that she does not allow sterile neutrinos on her laundry. In fact, these restrained siblings of normal neutrinos are often described as closed strings, just like gravitons. You would then not be limited to the D-Bran, but like the gravitons would be able to disappear into the extra-dimensional bulk - which presumably also the mentally high-dimensional woman does when she feels intellectually undersupplied at the party.


It is unclear whether there are sterile neutrinos. Some elementary particle models for uniting the forces of nature predict their existence. But an experimental proof is extremely difficult because sterile neutrinos are not even subject to the weak interaction like normal neutrinos - that is precisely why they are called “sterile”. They are only subject to gravity and perhaps exotic exchange processes with so-called heavy Higgs particles. But sterile neutrinos could very well play a heavy role in the universe: They are a good candidate for explaining the ominous dark matter. This makes itself felt through its gravity and rules the movement of galaxies and galaxy clusters. But it does not shine because it does not appear electromagnetically.

Nevertheless, sterile neutrinos would have to make themselves felt in other ways: Since ordinary neutrinos - there are three types of them - transform into one another, as has only been known for a few years, they could also sporadically transform into sterile neutrinos. These would also become normal neutrinos again, which then appear to appear out of nowhere. In fact, irritating things were measured in two experiments for the detection of neutrino conversions. One experiment, LSND (Liquid Scintillator Neutrino Detector), was already running at Los Alamos National Laboratory in the 1990s. The other, MiniBooNE (BooNE stands for Booster Neutrino Experiment), followed in 2002 at the Fermilab near Chicago. In both cases, over 1200 sensitive photomultiplier detectors in large mineral oil tanks were on the lookout for weak, sporadic flashes of light that actually existed. They were generated by neutrinos that penetrated the tanks from the outside. The results of both experiments are still controversial. They are contradictory and require even more and more precise data. This is because they do not match the predictions of the standard model of elementary particles, but could, under certain circumstances, be explained using sterile neutrinos.

Heinrich Päs contributed a special aspect. The studied physicist and passionate party-goer works after stays in Spain, Italy, the USA and Hawaii as a physics professor at the Technical University of Dortmund. Together with three colleagues, he showed how sterile neutrinos could outsmart the speed of light. The D-branes of string theory come into play again: if the bulk has at least one additional small spatial dimension and is curved or compressed, the sterile neutrinos would move faster than light in it - relative to the conditions on the bran. (Another thought for the discussion with the party girl: Perhaps the normal neutrinos are so light because their main mass is in the bulk - or to put it more precisely with Heinrich Päs: "The mass is suppressed as a transition from left- to right-handed particles, because the overlap of the bulk and the bran wave functions is small. "All right?)

Extra-dimensional neutrinos are an exciting hypothesis, because according to the special theory of relativity, movements faster than light can also be movements back into the past. That would be the case with tachyons, if they exist (Bild der Wissenschaft 2/2003, “Tachyons - faster than light”). In the case of sterile neutrinos that are faster than light, this would not automatically be the case. This requires a second compressed "large" extra dimension for the return journey. Otherwise the particles get into the relative past, but not back to their starting point.

Time zigzag after the big bang

If messages from earlier times were possible with sterile neutrinos, then there would be “time machines” everywhere in the universe - more precisely: everywhere in its higher-dimensional neighborhood. Some cosmologists are even thinking about whether time-traveling neutrinos could be an alternative to the cosmic inflation scenario. This is how many researchers explain the uniform temperature of the cosmic background radiation. This residual glow from the fireball stage is homogeneous with deviations of only 1 in 100,000 (see article “The Dark River” in this issue). If neutrinos zigzagged through time in the early universe, they could have caused this homogenization. The assumption of an inflationary expansion of the very early universe, which is met with skepticism by some cosmologists, would then be unnecessary.

"These ideas are wonderful and exciting," says Bill Louis of Los Alamos National Laboratory in New Mexico, spokesman for the MiniBooNE research group. “The only question is whether they are also true.” That cannot be decided at a desk, because no one can prove with calculations alone that there are sterile neutrinos and stable bulk rooms. The hypothesis can, however, be checked. If, for example, an asymmetrical behavior of neutrinos and their anti-matter partners, the antineutrinos, were measured, then that would speak against the bulk hypothesis, since sterile neutrinos make no difference. More precise measurements are therefore essential. The MiniBooNE successor is therefore already being designed at the Fermilab. The $ 15 million MicroBooNE project is said to have a tank with over 100 tons of liquid argon in which neutrinos can trigger ionizations.

In Heinrich Päs' scenario, several hypotheses build on one another, all of which have not yet been confirmed and are becoming increasingly exotic. There are:

Sterile neutrinos,

· At least one "large" extra dimension into which sterile neutrinos can escape (that would explain why normal neutrinos have such small masses),

· An asymmetrical compression or curvature of the extra dimension (this would enable the sterile neutrinos to take an effective faster-than-light "shortcut" and explain the LSND and perhaps also the MiniBooNE measurements),

· At least one second compressed “big” extra dimension (that would allow neutrino time travel to the past and perhaps also explain the uniformity of the cosmic background radiation).

Time order in danger

If the neutrino time loops were to be confirmed, this would have far-reaching consequences for our understanding of nature. In 1992, the famous physicist Stephen Hawking formulated a “conjecture to protect the order of time”, according to which the laws of nature do not allow time loops: time machines cannot be built or come into being - and if they did, quantum gravity effects would destroy them again immediately. Since then, physicists have calculated a few examples that confirm the assumption, but proof that it is generally valid is still pending. And so, in the context of general relativity, numerous "time machines" are under discussion: above all wormholes, but also cosmic strings, naked singularities, ring lasers and rotating mass concentrations (Bild der Wissenschaft 1/2006, "Time travel - when yesterday is tomorrow" ). Of course, they require exotic spacetime or boundary conditions such as negative energies and do not seem particularly suitable for everyday use.

It would be different with extra-dimensional neutrino time loops: They would put Hawking's conjecture to the test and would in principle be accessible at any location. “While we don't know where to look for a wormhole, the extra dimensions would be anywhere,” says Heinrich Päs. "Also, negative energies would only be necessary in a very mild form and only in bulk." If he is right, one does not need to worry about wormholes or extreme configurations of matter, but could study time warps here on earth.

He has already devised an experiment that would make such research possible: Send normal neutrinos through the earth, for example from the south pole into a detector at the equator. If they sporadically transform into sterile neutrinos and back again, then most likely with density differences such as between the earth's interior and the air. If ordinary neutrinos were to be measured at the equator before they were even sent off - the earth's rotation would help determine the time - that would be an indication that they have taken a six-dimensional shortcut as a sterile intermediate form, which worked as a time loop. Such an experiment could be feasible in a few decades. Until then, systems like MicroBooNE will do pioneering work.


Who knows - maybe the results of these experiments are already known thanks to capricious neutrino messages from the future - and “No strings attached” is the secret recognition motto of those who know. That would also explain why Heinrich Päs ‘research already appears in science fiction novels: in" The Accidental Time Machine "by Joe Haldeman and in" Die Würfel Gottes "by Mark Alpert. And why there is a quote from the American writer Jack Kerouac at the top of Päs' homepage: “We had finally found the magic land at the end of the road.” Is this the place where our Bran world ends, where strings no longer cling and where the bondage of time comes to an end? ■

by Rüdiger Vaas

Time leaps beyond extra dimensions

The familiar spacetime, according to string theory, could be a four-dimensional brane embedded in a higher-dimensional space. Sterile neutrinos (if they exist) could escape into this bulk. If the bulk is internally compressed and six-dimensional, i.e. equipped with two spatial dimensions more than the space-time we are familiar with, then the sterile neutrinos in it could even move faster than light - relative to the Bran. If normal neutrinos are now transformed into sterile ones and then back again later, the consequences would be unbelievable: they could be detected before they even started. They would have jumped into their own past.

Strings and branes

Bold hypothesis: Open “strings” should stick with their ends to “branes” (here a two-dimensional bran). Closed strings (such as sterile neutrinos and gravitons), on the other hand, can loosen and escape into the higher-dimensional “bulk” in the area.


· If there are additional dimensions of space and sterile neutrinos, these particles can fly backwards through time.

· That would explain strange anomalies in neutrino measurements and even the uniformity of the cosmic background radiation.



bdw editor Rüdiger Vaas describes the science and fiction of time travel, faster than light speed and other dimensions in detail in his current book:

TUNNEL THROUGH SPACE AND TIME Kosmos-Verlag, new edition 2010, € 19.95


Homepage of Heinrich Päs: www.physik.uni-dortmund.de/~paes/

June 15, 2010

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