Q: When will there be a reconciliation of quantum mechanics and general relativity. String theory with all its dimensions is not making a lot of progress. What do you consider as promising?
A: Nobody knows, and I would be suspicious of anyone giving a confident date. My guess is that we are still **decades rather than years** away from a generally accepted reconciliation of quantum mechanics and general relativity. The main obstacle is no longer simply inventing clever mathematics; it is finding **experimental evidence that discriminates between the competing ideas**. Recent work is encouraging because experiments with increasingly massive quantum systems may finally let us probe whether gravity itself behaves quantum mechanically. ([DOI][1])
If I had to bet, I would not put everything on one grand “theory of everything.” My preferred route would be a combination of **quantum information + emergent spacetime**, with **loop quantum gravity / causal approaches** as useful mathematical guides.
The reason is conceptual. General relativity tells us that spacetime is not a fixed stage: **spacetime itself is dynamical**. Quantum mechanics, by contrast, normally assumes that quantum systems evolve against some background notion of space and time. So perhaps the mistake is trying to “quantize spacetime” in exactly the same way we quantize an electromagnetic field.
I find the opposite possibility more attractive:
**Quantum information may be fundamental, while spacetime and gravity are emergent.**
Schematically:
**quantum relations / entanglement
↓
causal structure
↓
spacetime geometry
↓
Einstein’s gravity at large scales**
In this picture, spacetime would be something like **temperature**. Temperature is perfectly real, but there is no individual “temperature particle.” It emerges statistically from the behaviour of huge numbers of molecules. Likewise, curvature and perhaps even space and time themselves could emerge from an underlying quantum network.
That would also explain something otherwise rather mysterious: why Einstein’s equations look so much like thermodynamics. There are already deep connections among gravity, entropy, black holes, horizons and quantum information.
### Why I like this more than string theory
Your objection about dimensions is understandable, although technically string theory doesn’t arbitrarily add dimensions just to make the theory work: mathematical consistency leads to 10 dimensions for superstring theory and 11 for M-theory, with the additional dimensions assumed to be compactified. The much bigger issue for me is that it has produced an enormous landscape of possible low-energy universes and still lacks decisive experimental confirmation.
Loop quantum gravity takes Einstein more literally. It says, roughly, **don’t put quantum fields into spacetime — quantize geometry itself.** Areas and volumes then acquire discrete quantum structure. That is conceptually beautiful and requires four-dimensional spacetime rather than introducing extra macroscopic dimensions. But it remains unclear whether it reproduces all of known particle physics and classical spacetime naturally enough.
Other serious approaches include **causal sets, causal dynamical triangulations and asymptotic safety**. The fact that the 2025 Quantum Gravity conference still featured all of these alongside string theory and loop quantum gravity illustrates that the field has not converged on a winner. ([ISLQG][2])
### The experiment I would watch most closely
A fascinating change is happening now. Until recently people often said quantum gravity was experimentally hopeless because the Planck scale is around \(10^{-35}\) metres.
But researchers are now asking a simpler question:
> **Can gravity itself carry quantum information?**
For example, put two small masses into quantum superpositions and let **gravity alone** interact between them. If they become entangled, that might tell us something profound about whether the gravitational field has quantum degrees of freedom. The interpretation is subtler than originally hoped—work in 2025 showed that some classical-gravity models can imitate aspects of such entanglement—but these experiments are bringing quantum gravity into the laboratory rather than leaving it purely theoretical. ([Nature][3])
And that is why my rough prediction would be:
**5–15 years:** experiments begin seriously constraining what gravity can and cannot be at the quantum level.
**10–30 years:** we may discover a key principle—perhaps involving information, causality or emergence—that tells us which direction is right.
**30–100+ years:** potentially a mature theory comparable in status to GR or quantum mechanics.
But there is also a perfectly plausible possibility that the crucial conceptual breakthrough happens next year. Physics has done that before.
There’s one possibility I find particularly intriguing given our earlier discussion about AI, consciousness and separateness: **perhaps quantum mechanics and relativity appear incompatible because both space and time are emergent rather than fundamental.** If you remove spacetime from the bottom layer of reality, the conflict starts looking quite different. I can explain what such a “reality without fundamental space or time” might actually look like without much mathematics.
[1]: https://doi.org/10.1103%2FRevModPhys.97.015006?utm_source=chatgpt.com “Quantum-information methods for quantum gravity laboratory-based tests | Rev. Mod. Phys.”
[2]: https://www.islqg.com/2025-in-review/quantum-gravity-2025?utm_source=chatgpt.com “Quantum Gravity 2025 | ISLQG”
[3]: https://www.nature.com/articles/d41586-025-02509-7?utm_source=chatgpt.com “Is gravity quantum? Experiments could finally probe one of physics’ biggest questions | Nature”
