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The media is currently reporting on a new idea in theoretical physics, developed by the group of professor Jonathan Oppenheim, to unify general relativity with quantum theory. The novel idea is not to quantize general relativity, which is assumed to be the most promising idea and as is central to string theory and loop theory, but instead to allow classic fluctuations in spacetime at a sufficiently small scale.

The following article gives an insight in how these fluctuations may lead to unification: https://www.sciencenews.org/article/gravity-quantum-mechanics-physics-theory

The famous two-slit experiment apparently plays an important role. Due to the spacetime fluctuations, a particle such as an electron behaves like a wave, which experiences interference in the two-slit experiment and thus causes the well-known interference pattern on the screen.

If this is correct, then the new theory seems to solve one of the great questions in physics: why does a particle with momentum $p$ acquire wave-like behaviour with a wavelength prescribed by De Broglie's formula $p = h/\lambda$ ?

Can it really be so simple? What do the experts think?

M. Wind
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Can it really be so simple ?

Almost certainly not. Otherwise everyone in the physics community would be convinced already; eye-watering amounts of funding would become available; and multiple teams would be hard at work building experiments to demonstrate the theory so that they could win a Nobel prize. Scientists are evidence-led, but that does not make them closed-minded.

What do the experts think ?

Carlo Rovelli hasn't paid out on his 5,000-to-1 bet yet. Oppenheim leads a team at UCL and has a credible track record in quantum physics, so his "postquantum theory" isn't entirely crackpot, but consensus seems to be that it is still a long shot.

gandalf61
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The novel idea is not to quantize general relativity

Not true, because all fundamental fluctuations are of quantum nature. Quantum Field Theory states that all fields undergo quantum fluctuations, and if gravity is a field, then sure it must fluctuate too. But to deeply understand these space-time fluctuations we must come up with a theory which best describes these micro changes of gravity.

Take for example, Uncertainty principle, $$ \sigma _{x}\sigma _{p}\geq {\frac {\hbar }{2}} \tag 1$$

which relates particle momentum and coordinate fluctuations, with a Planck constant. (By the way, notice $\hbar$ in (1) equation, this means that fluctuations are quantized, and so if space-time fluctuates at the fundamental level, then it also should be quantized.) But this equation is just a precursor to the full-scale QM theory based upon wavefunction, probability densities and Schrodinger equations.

Similarly, if we just state (and find-out) that space-time really fluctuates, but will not come-up with a Physics framework which would explain deeply the roots and boundaries of this type of fluctuations,- our understanding of gravity will never be complete.

So the claim "New theory for unifying general relativity and quantum mechanics" is just ridiculous,- authors just lay-out some pre-cursor work to a greater things in gravity research.

Agnius Vasiliauskas
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