Against Spacetime by Giovanni Amelino-Camelia

Giovanni

Again want to go back to the issue of the divorce of space and time and again to ask you to read my essay.

Hi Giovanni

Good to note that space-time is questioned by forward thinking professionals who realise something has to give such that QM and gravity can find a common underlying structure.

You write: " v=sqrt[(E-U)/m]. 聽Since in quantum tunneling E − U < 0 this recipe for the speed (and therefore the corresponding derivation of the travel time) becomes meaningless."聽

Why meaningless, trust the mathematics; accept imaginary velocities. This you can do by adopting a hyper-space where each axis is complex.

Exactly such a complex hyper-space I propose in my essay, your comment to this idea would be interesting.

Regards

Anton @ ( 聽../topic/1458 聽)

I read your arXiv:1206.3805 paper a couple of time. I don't have time to write at length right now. However, this structure seems to be very similar to twisters. In fact I have today been thinking quite a bit about how one could construct T-theory with q-deformations. I will try to write more about the connection with T-theory after I have tried to bend metal on the idea.

I gave your paper a high score. It deserves it and I think it should be ranked higher on the list than it has been.

Cheers LC

Giovanni,

You would change Einstein's 1905 false light postulate only for the sake of your career, right?

http://www.nature.com/nature/journal/v418/n6893/full/418034a.html

Giovanni Amelino-Camelia: "Galileo-Newton theory was superseded by Einstein's theory of special relativity, but, after a century of success, that too is now being questioned. (...) Special relativity has only one absolute scale: the speed of light is the same for all observers, in all frames of reference; for particles with mass, the speed of light is the maximum attainable velocity. Last year, I proposed that the introduction of a second absolute scale, CHANGING THE POSTULATES OF SPECIAL RELATIVITY, would fit the needs of some quantum-gravity approaches and would affect the analysis of cosmic rays."

Pentcho Valev pvalev@yahoo.com

The connection to twistor theory is I think not hard to see. The boost operator P_μ that acts on [x_i, x_0] = ilx_i such that

P_μ > [x_i, x_0] = il P_μ > x_i

The coordinates (x_j, x_0) we write in spinor form

x_j = σ_j^{aa'}ω_{aa'}

x_0 = σ_0^{aa'}ω_{aa'},

where ω_{aa'} = ξ_a ω_{a'} ξ_{a'}ω_a. This commutator has the form

[x_i, x_0] = σ_j^{aa'}σ_0^{bb'}[ω_{aa'}, ω_{bb'}]

= iC^{cc'}_{aa'bb'} σ_j^{aa'} σ_0^{bb'} ω_{aa'}

= i|C| σ_j^{aa'}ω_{aa'}

where the magnitude of the structure matrix is |C| = l. In general this may be written for

x_j = σ_j^{aa'}ω_{aa'}

x_0 = σ_0^{aa'}ω_{aa'} iq_{aa'}π^{aa'},

where the commutator [ω_{aa'}, π^{bb'}] = iδ_a^bδ_{a'}^{b'} and the general form of the commutator is then

[x_i, x_0] = i|C| σ_j^{aa'}ω_{aa'} iσ_j^{aa'}q_{bb'}[ω_{aa'}, π^{bb''}

[x_i, x_0] = ilσ_j^{aa'}ω_{aa'} - σ_j^{aa'}q_{aa'}.

The boost operation B = 1 a^l_jP^j on the commutator [x_i, x_0] is then equivalent to the commutation between spinors [ω_a, ω'_b] for ω'_b = ω_b iq_{bb'}π^{b'},

[ω_a, ω'_b] = [ω_a, ω_b] iq_{bb'}[ω_a , π^{b'}]

= C^c_{ab} ω_c iq_{ab}.

This could be explored more deeply. Ed Witten demonstrated the "twistor revolution" in string theory. If twistors are connected to κ-Minkowski spacetime there might then be a link between string theory and LQG and other "edgelink" type of quantum gravity theories. This would be potentially interesting, for this might serve to correct the difficulties with each of these.

Cheers LC

Greetings Giovanni,

I would like to suggest the problem with Spacetime is that physical events are considered to be 'instantaneous' at time t. This fundamental assumption is in conflict with the Second Law of Thermodynamics which can be shown to state "every physical event needs some positive duration of time to occur" (see my Chapter, "The Thermodynamics in Planck's Law" ). Thus, the Second Law establishes 'physical time' to be 'duration' Δt and not 'instantiation' t . Each moment of a particle moving along a smooth worldline is a 'physical event' requiring a positive duration of time to occur. Spacetime violates this requirement of the Second Law. This, in my opinion, explains why Cosmology is in conflict with Thermodynamics.

Constantinos

"The Metaphysics of Physics"

Dear Giovanni,

I read your essay with great interest. A few remarks/questions.

1. I agree wholeheartedly that modeling classical spacetime as a manifold over the continuum is at the very best redundant. Some would argue that it "does no harm" and that it "makes no difference" what the structure is at arbitrarily small scales, but something that bothers me about this view, in addition to the issues you raise (tunneling, etc.), is the fundamental role the representation theory of the Poincare symmetry group of Minkowski space plays in constraining the properties of particles in quantum field theory. I do not think it is at all obvious that altering this symmetry at small scales would have no practical effects.

2. What is your favorite interpretation of quantum theory? I ask this because it seems to me that the conceptual role of spacetime depends on this to a large degree. For instance, if you prefer a sum-over-histories view, you can separate the properties of classical spacetime from quantum effects arising through superposition of universes. If you prefer to think about a single universe and view classical physics as a limit via the correspondence principle, then it seems clear that such a universe is very unmanifold-like.

3. On a related note, one possible way of thinking about nonlocality is to provisionally banish the spacetime metric and simply regard direct influence between events as defining locality. The idea is that spacetime is a way of talking about relations among events, that it closely resembles a Lorentzian 4-manifold at large scales, but that "nonlocal interactions" with respect to the metric of this "nonphysical manifold idealization" are simply indications that the manifold is really fictional. Personally, I tend to think that the most prominent nonlocal phenomena such as entanglement have more to do with superposition than nonmanifold structure, but I do think that the large-scale properties of spacetime arise from more primitive microstructure, or, more conservatively, that models based on primitive microstructure will eventually outperform manifold models experimentally. See my essay here for more on this: On the Foundational Assumptions of Modern Physics.

3. I will have to have a look at your papers about observer-dependent association of processes to points in noncommutative spacetime. That is an idea I have not heard of before.

Thanks for the enjoyable read. Take care,

Ben Dribus

Giovanni,

If the absurd "energy-dependent but observer-independent" speed of light is a failure, why don't you try, for a change, "energy-independent but observer-dependent" speed of light? I am not sure about the energy independence but "observer-dependent speed of light" sounds quite reasonable. I have tried to show this in my essay:

http://fqxi.org/community/forum/topic/1398

Pentcho Valev

Dear Giovanni,

I appreciate the response! I think we agree on how quantum theory should be viewed in general. As you suggest, however, different interpretations might generalize in different ways. For example, in Feynman's original sum over histories formulation (the 1948 paper), he sums over "particle trajectories" on a fixed background. If you believe GR, though, you know that the "spacetime" itself should respond in different ways to different trajectories, so each trajectory has its own spacetime, and suddenly you are summing over universes, but the underlying concept of a sum over histories comes through unscathed. The alternative formulation of a probability density function on spacetime, which works fine for a fixed background, doesn't generalize as easily to the background-independent scenario. Take care,

Ben

Giovanni

Can you advise if light passes through the visor material of your helmet at the constant speed c/n irrespective of the speed at which you are driving?

If so, have you considered that, as your visor is equivalent to a lens medium, CSL may then be simply explained by light changing speed on arrival at your visor or lens. Wavelength and thus frequency also change (inversely) because c (as c/n) is conserved in both the rest and co-moving (bike) frame.

The boundary condition between frames is the equivalent to dynamic fluid coupling at the surface fine structure of all dielectric media, including the diffuse ISM.

You did indicate you'd try to read my essay, I hope you may soon get there and comment. It considers this 'discrete field' model and boundary mechanism in detail, also with a little theatre. I have been unable to falsify it, found the implications broader than they may at first appear.

Many thanks in advance. PS, I confirm I still think yours is worth a far higher placing and intend to help it achieve that.

Best wishes

Peter

For better clarification my approach

I sending to you Frank Wilczek's 3 keen articles

http://ctpweb.lns.mit.edu/physics_today/phystoday/Abs_limits388.pdf

http://ctpweb.lns.mit.edu/physics_today/phystoday/Abs_limits393.pdf

http://ctpweb.lns.mit.edu/physics_today/phystoday/Abs_limits400.pdf

All the best

Yuri Danoyan

Giovanni,

{link:http://fqxi.org/community/forum/topic/1304]The problem as I see it[/link], is that we perceive time as a sequence from past to future and physics re-enforces this by treating it as a measurement issue, ie. clocks, detectors, days, etc, but the physical reality is the changing configurations turn future into past. It is not the earth traveling a narrative dimension from yesterday to tomorrow, but tomorrow becoming yesterday because the earth rotates. In this way, time is an effect of action. Like temperature it emerges from that basic thermodynamic activity. Clock rates vary, as levels of activity vary. More activity, faster clock rate. If time were a dimension from past to future, one would think a faster clock rate would travel into the future more quickly, but the opposite is true. As it ages/burns quicker, it moves into the past faster. The twin in the faster frame is dead when her twin in the slower frame returns.

Duration is not some dimension that transcends the present, but is the state of the present between detections.

Since the lightcone of any event is incomplete prior to the event, the future is probabilistic, even if the laws determining its outcome are deterministic.

It is the collapse of probabilities which yields actualities, so the cat is not both dead and alive, because there is no external timeline moving the present from past to future, but the actual occurrence of events turning future into past.

Cause and effect is not sequence, but energy exchange. Yesterday didn't cause today, any more than one rung on a ladder causes the next. It is the sun radiating on this rotating planet that creates this sequencing called days. Time is an effect, not a cause.

Knowledge is created inductively, as future becomes past, but is used deductively, as the past is used to predict the future.

link

Giovanni,

You will get maximum rating from me. Something tells me you share Magueijo's and Smolin's conviction that "the root of all the evil is special relativity":

Joao Magueijo, Faster Than the Speed of Light, p. 250: "Lee [Smolin] and I discussed these paradoxes at great length for many months, starting in January 2001. We would meet in cafés in South Kensington or Holland Park to mull over the problem. THE ROOT OF ALL THE EVIL WAS CLEARLY SPECIAL RELATIVITY. All these paradoxes resulted from well known effects such as length contraction, time dilation, or E=mc^2, all basic predictions of special relativity. And all denied the possibility of establishing a well-defined border, common to all observers, capable of containing new quantum gravitational effects."

Pentcho Valev