As some background, I really don't know all that much about physics except what I study in school. So, this question might make me sound like a noob, but I hope I can be beared with.

Anyway, I watched a video explaining string theory(Brian Greene's at TED), more in layman's terms, and the speaker said that the supercollider at CERN (which was still under construction when the talk was given), could help prove string theory. He also said that the way that that would be proven was that when high speed particles collided, it would be observed that some of the debris get injected into previously undiscovered dimensions.

And we would know that this happened if the energy of the system measured after the collision is slightly less than the energy before the collision, because some of the mass and energy are in other unknown dimensions.

But I also read later, that the collider hasn't yielded any such results even after almost a decade of research.

So, my question is, what if the devices we have for measuring these energy changes, unknown to us, are affected by or take into consideration even these higher dimensions? Then, maybe string theory is correct and the debris from these collisions are being injected into higher dimensions, but our readings don't show it because our readings, unlike us, are counting these higher dimensions too.

But I'm not really sure about this because I'm no physics expert and I've only heard of string theory being explained in layman's terms. So. there's maybe more to the picture than what I'm currently seeing. But at the risk of sounding like a total noob, the above is my question.

  • 3
    $\begingroup$ The problem with this kind of question is that there is no way of answering it. It is always possible something weird multidimensional happens... but we have no way of analysing it except through currently known theories. One can of course give an answer about how detectors work in extra dimension theories and why your scenario is unlikely, but it is likely to be pretty incomprehensible to you, which kinds of defeats the point of asking the question. $\endgroup$ Jun 7, 2021 at 13:25
  • $\begingroup$ Welcome to physics stack exchange! It's probably true that this question lacks a unique answer, but it may be answerable within specific frameworks (such as every model -- string-theoretic or otherwise -- that uses the same description of extra dimensions). Still, it's a good question for anyone trying to better understand this particular model of extra dimensions. The most advanced students would be able to figure it out on their own, but anyone else might come here for answers ;) $\endgroup$
    – Natavi
    Jun 7, 2021 at 14:36
  • $\begingroup$ This may be a misunderstanding, but I think it is a question slightly more about particle detectors than string theory, so I gave it a shot. $\endgroup$
    – Koschi
    Jun 7, 2021 at 14:39
  • $\begingroup$ String theory predicts the escaped energy wouldn't be detected. That's not to say results so far refute string theory, just that we haven't reached an energy scale at which a notable about of energy escapes as you described. (String theorists aren't sure at what scale it ought to happen, but they hope it's low enough we can detect this with contemporary or near-future technology.) $\endgroup$
    – J.G.
    Jun 7, 2021 at 16:03

2 Answers 2


I am more educated on the theory side of particle physics, and neither an expert in string theory, nor experimental particle physics, but nevertheless I hope my answer helps to question some of your understanding of detectors, and further develop your question. It just focuses on your idea that a machine as big as a particle detector could, without our knowledge, detect energy of particles in extra dimensions.

The extra dimensions string theorists talk about are assumed to be very tiny. This means that they are NOT spatially extended as our three usual spatial dimensions we live in, but are tiny (usually as small or smaller as what we, at the moment, call fundamental particles) and most probably finite in the sense as, for example, a circle would be... you could move along a circle, but if the circle is very tiny you get back to where you started very soon. Only things that are as small as these dimension could penetrate them, so we cannot excess them with any microscropic and especially no macroscopic device to date. I am not sure if there are concepts of additional large dimensions, a string theorist would need to correct me here, but if you hear about a ten-dimensional superstring theory, this usually means that six spatial dimensions are very tiny, finite, and can only be accessed by things existing on that small scale. Note that this implies that a particle "vanishing" into an extra dimension does not "fly off" in an unknown dimension in the usual sense, since the extra dimension is not spatially extendend. How it would conceptual works for a particle to vanish in such a extra dimension at all is beyond my knowledge. But let's suppose it can somehow vanish into one of these for now.

Now, the detectors in particle accelerators are no black boxes that just spit out the total energy that came out a particle collision, but they are huge machines (look at CMS and ATLAS) that combine different structures to measure paths and energy deposits of the particles that penetrate them. Meaning: A particle detector measures the total energy of the resulting particles not directly, but this is calculated by the readout of the trackers (that can track the path of a particle, and therefore gives a notion on their charge, since the path bends in a magnetic field, while they do not measure energy directly) and by the calorimeters (that detect collisions of the resulting particles on their way "out of" the detector and measure the energy transferred by the collision at various points in the detector). Note that this is a very (!) crude explanation.

So in my opinion I would not know how, without our knowledge, these detectors actual measure energy of particles that vanished in unknown dimensions, since the detector relies on particles actual moving through it. Also note that there ARE particles, the neutrinos, that cannot be detected by the detectors used in particle accelerators and that lead to some missing energy. We do not expect neutrinos to vanish in extra dimensions, but just to leave the detector without interacting with anything.


It is a good question. So you basically have two options to explain the data:

a) no extra dimensions and your current established theory holds and explains all data

b) an additional feature for the particle theory (extra dimension) and a very delicate cancellation with probably another theory needed for the particle detector functonality.

While nobody came up with a theory needed for b) it might be possible. And it will be impossible to distinguish a and b (expect if b makes some other predictions), but for now a and b cannot be distinguished.

Here Occams razor comes as a fundamental guiding principle into play. It basically says: if you have two theories which have the same output, you choose the one which is simples/requires less assumptions.

This happens all the time in physics. You could surmise that little angels push round object while little devils pull them so that the effect on newtonian motion cancels. But then you say: do I actually need these assumptions? Do they help explain experiment or can I get away with them?

  • $\begingroup$ Downvoters can you explain? I mean what I am saying is nothing new, stuff like this is usually stated in theoretical physics 101 $\endgroup$
    – lalala
    Jun 9, 2021 at 7:07
  • $\begingroup$ About angels pushing (no devils pulling) cf feynmanlectures.caltech.edu/I_07.html $\endgroup$
    – lalala
    Jun 9, 2021 at 14:03

Not the answer you're looking for? Browse other questions tagged or ask your own question.