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FQXi BLOGS
May 20, 2019

CATEGORY: Blog [back]
TOPIC: Experimental Tests for String Theory? Guest post by Anil Ananthaswamy [refresh]
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FQXi Administrator Zeeya Merali wrote on May. 10, 2010 @ 12:53 GMT
From Anil Ananthaswamy:

One of the joys of writing a book on modern physics, especially cosmology, is that you get to tackle some mind-expanding concepts, such as string theory and the multiverse. But when the book is about extreme experiments and how theory and experiment need to get back in lockstep if physics is to move forward, then string theory presents a peculiar challenge. On one hand, it remains far removed from experimental verification. On the other, it constitutes a significant chunk of physics theory these days, making it hard to ignore.

This was the challenge I faced while writing The Edge of Physics. How could I write about experiments and yet address string theory? I chose to focus on two ideas that are experimentally relevant, and have some connection to string theory.

The first is the possible discovery of supersymmetry at the Large Hadron Collider. Supersymmetry (SUSY) is an extension to the standard model of particle physics, and it posits that every particle we know of has a partner particle. The symmetry is between fermions and bosons, so that every known fermion has a supersymmetric bosonic partner, and every known boson has a supersymmetric fermionic partner. These supersymmetric particles would have existed in the early universe, and would have decayed soon after the symmetry was broken. Since we haven’t seen any in particle colliders yet, such particles, if they exist, must be very heavy. The LHC is hoping to create supersymmetric particles, if supersymmetry exists at the teraelectronvolt (TeV) energy scale.

What’s this got to do with string theory? Well, most string theory models require the universe to be supersymmetric. So, if the LHC finds SUSY, it would be a boost for string theory. But the universe can be supersymmetric without being stringy – so finding supersymmetry is not a proof of string theory.

Also, if the LHC does not find SUSY, it does not mean the universe is not supersymmetric – it could exist at energy scales beyond the LHC’s reach. So, not discovering supersymmetry at the LHC does not disprove string theory.

The other experiment that is of some relevance to string theory is the precise measurement of the curvature of the universe. For all practical purposes, spacetime seems to be flat, the curvature equal to zero. But the error bars on existing measurements are enough to allow for either a slightly positive or negative curvature. And experiments like the European Space Agency’s PLANCK satellite and the proposed Square Kilometre Array (the world’s largest radio telescope) will measure the curvature of spacetime with great precision. (The photo at the top of this post shows a prototype dish for the Karoo Array Telescope near Johannesburg; the SKA might have 3000 such dishes...)

Again, what’s this got to do with string theory? There’s a controversial prediction from string theory that the curvature of spacetime should be ever-so-slightly negative (an open universe). This comes from the idea of the landscape of string theory, a collection of 10500 or more vacua of spacetime. Our universe would have emerged through a series of tunneling events, as one vacuum morphed into another, eventually ending up with ours. (Check out this week’s classic article, “The Universe’s Odyssey?” for more about that.) This process predicts a slightly negative curvature. A measurement of a positive curvature, however small, would cause considerable consternation for this model of how our universe emerged.

Given the preoccupation with string theory (among groups both for and against it), it’s no wonder that almost each and every time I have talked about The Edge of Physics, someone in the audience has invariably asked: What can these experiments tell us about string theory? It’s clear that string theory is not just a significant chunk of physics research, it has also grabbed people’s imagination. Whether we’ll have any answers soon is open to debate.



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Lawrence B. Crowell wrote on May. 10, 2010 @ 22:54 GMT
I have one problem with this. For k = 0 in the FLRW metric space is flat, but spacetime may be curved. A cosmological constant is a Ricci curvature term which defines how spacetime is curved. It means that the flat space on the Hubble frame defines a foliation where points are being slid apart by the curvature of spacetime.

Cheers LC

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Eckard Blumschein wrote on May. 12, 2010 @ 04:06 GMT
Aren't Friedman-Robertson-Walker, and other stuff based on an a priori given spacetime to move within back and forth? Given Ritz was correct with his argument that future events cannot influence the past, shouldn't we be open for really foundational questions?

Eckard

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Lawrence B. Crowell wrote on May. 13, 2010 @ 02:04 GMT
No there is no backwards causality in FLRW spacetime. The equations of motion or the Einstein field equations are second order and so time reversal invariant, but that is different from saying there are closed timelike geodesics or backwards causality.

Cheers LC

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John Merryman wrote on May. 13, 2010 @ 09:53 GMT
When the future becomes more past, it adds additional lenses through which events further in the past are both distorted and clarified, much as gravity fields distort and magnify the light of more distant sources.

Anyone willing to bet that no matter how carefully it's measured, the universe will continue to be flat?

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Eckard Blumschein replied on May. 15, 2010 @ 20:50 GMT
Dear John Merryman, I appreciate the chance for hopefully forcing you and many others to rethink an understandable but inappropriate metaphor. You will certainly admit that your metaphor of lenses through which one can see a less blurred picture of the future refers to a brain, not to light. Having a second sight means being clairvoyant in the sense of making a correct guess. Does this have something to do with physics? No, not even if a prediction is made on the solid basis of physical laws. You know there is no Laplacian demon. The future is always more or less open. How much does not matter in principle. Conversely, there is absolutely no way in reality to influence what has got history. We all are trained to foresee something that does not yet exist. Be honest: Is there really an observable future?

I say no, and I conclude from that: Future spacetime is unphysical science fiction.

Increasing distance corresponds to increasing elapsed time. Both are not negative in reality. While the light cone of past can be meant to denote reality as well as fiction, the light cone of future definitely belongs only to fiction.

Regards,

Eckard

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John Merryman replied on May. 16, 2010 @ 00:17 GMT
Eckard,

I was not talking about the future, but the past.

My point is that the past is not physically real. No, we cannot go back and change what happened, but these events are constantly receding ever further into the past and since there is no god-like perspective in which all events exist in some pure form, than any subjective perspective of these events is constantly changing, due to the further passage of time. For me, from a strictly physical perspective, the past is not the narrative series of events leading up to the present moment, but all evidence of prior moments existing in the present moment and from that view, it is like entropy, constantly breaking down and falling away, to be replaced by new forms.

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Georgina Parry replied on May. 16, 2010 @ 22:37 GMT
Eckard,

You said ."I say no, and I conclude from that: Future spacetime is unphysical science fiction." I agree there is no observable future only prediction or imagination.

We do experience relativity though. So that which is one persons future may be another's past. Thinking of a thunder storm. The far observer hears the thunder in the near observer's future. The near observer heard it in the far observer's past. Therefore to model this experience there must be a span of time including both future and past. Distant objects are seen in the past but as they are approached the time difference between observer and observed object decreases until they are in the same now.

It takes time to move towards an object. So the distant village that I see (past image of it) may be half an hours walk away whereas the the wall of my room a few seconds away. Objects are experienced as temporally separated. The problem is when this experience is considered to represent existential material substance in space rather than just a mental construct. If objects actually exist spread throughout time there must be countless copies of each object, if each time space has its own version. Where does the energy and substance come from to allow for replication of multiple copies of every object distributed through time? As you have said, "space-time is unphysical science fiction." It is a model based on temporal experience not existential spatial reality.

In spatial reality there is no future and no past only now and a changing configuration of substance within it. The past and future are imaginary realms. The past is the record of change only. It can not be physically altered in any way that could effect now. The future likewise does not have physical existence and can not have any influence on the now.The results of sub atomic scale experiment should not be expected to fit with relativity, because these experiments are not concerned with human experience of reality but what is happening in objective unobservable space. In my opinion.

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Eckard Blumschein wrote on May. 13, 2010 @ 23:16 GMT
When predictions may become more real, they nonetheless remain uncertain and open to possibly unseen influences, in principle. Do not blur the distinction between the always open system of reality, which evades complete knowledge of all possible influences, and any model of it, being always limited to known influences. When this distinction seems to be problematic then the reason can be ascribed to imprecisely defined events.

One cannot measure and predict the same value of a quantity at a time. When Minkowski united past and future along a common time scale, he just followed the bible "from eternity (minus infinity) to eternity (plus infinity). God's point of view is unphysical in so far as God is not restricted to see what already happened but He anticipates anything while physics can only measure and store data from the past.

Accordingly, physics has to get aware of the necessity to distinguish between either an observing point of view that is restricted to what is the past relative to the moment of consideration or an abstract and therefore unbound arbitrarily chosen point of view. Spacetime assumes the latter.

In order to get rid of arbitrary choices and confusing imaginary time, one may consider squared distance instead of x^2+y^2+z^2 and equal it to squared ct. Negative distance is as unphysical as is negative elapsed time.

This reasonable restriction does not imply that one also may take advantage from time to come. It is just a different consideration. Claiming to unite past and future, spacetime fails to correctly describe reality.

In daily life, we also need two values of time, an arbitrarily agreed reference and the very moment relative to it. For the number of birthdays I already celebrated, it does not matter when Christ was born. Those who prefer to judge on the basis of mathematics should be warned: Many details in mathematics have been adapted to our traditional understanding of time. That's why my seemingly simple arguments are overly foundational.

LC, I consider pure oscillations mere approximations and strictly speaking as unphysical as the sin function from -oo to +oo. I guess, even the earth will not for ever rotate as it presently does. I agree that we must not conclude from time reversal invariant equations that the reality is anticipatory. To my understanding tho world is not made of equations even if the bible says in the beginning was the word. Incidentally, I do not see differential equations the primary ones.

Eckard

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Georgina Parry replied on May. 14, 2010 @ 05:28 GMT
Well, said Eckard. These are important ideas that need to be more widely appreciated.

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Jason Wolfe wrote on May. 14, 2010 @ 06:43 GMT
Eckard,

I also agree with you. Your comment that God is not limited by events that have already occured is very interesting. Some would mistake this to mean time travel; but that would be an incorrect interpretation. God does span time in a way that cannot be logicaly explained. To say that God anticipates is more reasonable. I think all you'll find here is a mind-bender.

Anyway, your ideas are good.

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Eckard Blumschein replied on May. 14, 2010 @ 16:33 GMT
Zeh quoted from Dukas and Hoffman an utterance by Einstein: "For us believing physicists, the division into past, present and future has merely the meaning of an albeit obstinate illusion".

I agree with Zeh in that this is a 'divine world picture'. However, I do not see it based on relativistic spacetime but the other way round spacetime is based on nothing but the divine world picture of a block universe. Those who believe in the latter will perhaps be unable to purify the fertile principle of relativity from futile attempts to incorporate what I consider Minkowski's mistake. Maybe, M. died because he felt being not entirely correct.

Eckard

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Eckard Blumschein wrote on May. 14, 2010 @ 22:40 GMT
Because I am just a bit familiar with the antennas, I was impressed by an exhibition that demonstrated how much is known with high precision at least about our solar system. If there are still important huge "white areas" to be discovered then perhaps in the very foundations of science. Less hype but readiness to critically and carefully reconsider even Nobel price awarded attitudes would perhaps be more appropriate.

Why does e.g. Schulman see an alternative between symmetry in QM but asymmetry in the large? Isn't there a necessity to categorically distinguish between either reality's one-sided restriction or divine freedom to arbitrarily manipulate the abstracted timescale at will? I see IR+ not necessarily a part of IR. IR * can be mapped on IR and vice versa.

Admittedly, one must not blame the physicists for ignoring the fact that reality is something quite different from canonical theory, no matter how well the latter seems to fit. Every intelligent human tends to benefit from tolerating speculative mingling of reality with possibility. Share holding is funny.

Given we realize that the notion timespace originates from an untestable and perhaps misleading belief. What if any harmful consequences will this correction imply to the principle of relativity?

Eckard

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Georgina Parry replied on May. 15, 2010 @ 06:25 GMT
Eckard,

I don't think there will be a harmful consequence for relativity.It will still work, as it does now. It will still give good predictions of what will be observed at the macroscopic scale. It will just regarded differently. (Hopefully as a model of experience rather than underlying physics.)

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John Merryman wrote on May. 17, 2010 @ 02:39 GMT
Eckard,

There are implicit and explicit aspects of relativity that would need to be reconsidered. Rather than being a "persistent illusion," the present would be the totality of reality. Rather than spacetime being a geometric presence which tells matter and energy how to move, this dimensional coordinate system would be one more reductionist map. While time would be removed to a second order effect of motion, similar to temperature, the vacuum of space would be the equilibrium state for this motion.

There would be a range of conceptual changes as well. Effects, rather than objects, would be more readily understood as fundamental.

Viewing time as an effect of motion, rather than a dimension to be traversed, will have a fundamental effect on humanity's relationship with nature. By and large, western thought is based on this linear motion of objects against context, whether literally or figuratively. "In the beginning was the Word and the Word was God." sets this whole linear construct in motion. Our religions are, in their most fundamental structure, if not the goals they seek to attain, fundamentally narrative constructs. Not only the stories they tell, but the beginning to end singular history that binds people into one unit. Even now, the Big Bang theory attempts the same unification of all stories into one. What Relativity tried to do, was one final effort to braid the broad tapestry of multiple, interlocking, but differing relationships into one construct,one large, but fraying rope. Though the forces pulling against it left it bent and twisted, such that even the present being physically real had to be rejected.

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Georgina Parry replied on May. 17, 2010 @ 09:04 GMT
John, Eckard,

John,

you said "There would be a range of conceptual changes as well. Effects, rather than objects, would be more readily understood as fundamental."

I think that is a very important point. It is relevant to how the Universe is perceived too. It is said in general parlance that -everything has a beginning and an end. This is generally considered to apply to the universe too. However within nature many processes occur that are cyclical and do not have such an apparent beginning and end. Nitrogen cycle, water cycle, Kreb's citric acid cycle, life cycle etc. Although the individual constituents within the cycle alter, the cycle itself is continuous. It would therefore perhaps be more appropriate to think of the objective Universe as cyclical process rather than an object.

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John Merryman replied on May. 17, 2010 @ 09:45 GMT
Georgina,

Probably more importantly, cycles within cycles and along side other cycles, all binding everything together, as opposed to some overarching cycle, because we keep trying to isolate one particular entity or process and ignore the mass effect. Much like in Barbour's essay, where he still tried to isolate out the most efficient motion as the basis of time, while it is all motion, creating an infinite variety of clocks, that creates the overall effect of time.

Another example of the western focus on the object as fundamental is in the assumptions behind particle colliders, LHC, etc, where they try discovering the context as some deeper field of particles, the Higgs, by crashing particles into each other. It's sort of like trying to understand automobiles by crashing them into each other.

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Georgina Parry replied on May. 17, 2010 @ 10:04 GMT
John,

OK I agree. Isolating one overarching process would not entirely explain the whole. Though all of the internal cycles, as you described, could still be viewed as forming or being formed from a holistic, cyclic, super process. Rather than an object.

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Ubermensche physicist wrote on Aug. 4, 2010 @ 23:08 GMT
A 4-dimensional space could be represented as the average of a 6 dimensional space and a 2-dimensional space.

6 dimensional space would be quantum mechanical and gravito-electromagnetic, insofar as it would involve a further division of the three dimensions BY HALF.

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Anonymous wrote on Aug. 4, 2010 @ 23:26 GMT
U.P. -- dimensions may be fundamentally/mathematically multiplicative as well. The space could be 3D as well (2x3=6)

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FAST FRED wrote on Aug. 5, 2010 @ 18:23 GMT
An averaging of space (in 6 dimensions/directions) constitutes and averaging/balancing of attraction and repulsion, and of energy and gravity.

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The Lightbringer wrote on Aug. 5, 2010 @ 18:32 GMT
FAST FRED, Anonymous, U.P. -- excellent. This accomplishes an averaging/balancing of distance in space (as well) as a function of balanced attraction and repulsion. It explains gravitational/electromagnetic expansion and contraction.

Constancy of energy, repulsion, inherent attraction, variability/mutability of forms -- it has it all.

We would be incapable of growth and becoming other than we are if we were unable to comprehensively represent and integrate the forces/understandings of physics.

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FAST FRED wrote on Aug. 5, 2010 @ 18:43 GMT
Lightbringer, correct. The gravitational middle level of feeling/energy grounds it and centers it.

The proportionate reduction of BOTH GRAVITATIONAL FEELING AND THOUGHT PUTS THIS FUNDAMENTAL FORCE OF LIFE/NATURE RIGHT AT THE CENTER OF THE BODY (Think growth of the baby!) AND IN KEEPING WITH THE NATURE OF DREAMS AS WELL.

DiMeglio leads physics. Sorry that he has knocked so many of you out of the game/ring.

String theory is exploring the nature of dreams insofar as it has/can have any legitimacy. Again, sorry folks. Don't shoot the messenger (DiMeglio).

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Anonymous wrote on Aug. 5, 2010 @ 19:10 GMT
Lightbringer, this is superb, and fundamentally important, you said: "We would be incapable of growth and becoming other than we are if we were unable to comprehensively represent and integrate the forces/understandings of physics."

Keep up the great work. Don't worry about the others who you are defeating and proving wrong and incompetent here.

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songjoong sdfsd df wrote on Dec. 27, 2017 @ 07:20 GMT
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