Dr Brian Keating | String Theory's Leading Contender Disproven? @DrBrianKeating | Uploaded September 2024 | Updated October 2024, 16 hours ago.
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Is loop quantum gravity wrong?
The leading contender to string theory, loop quantum gravity (LQG), may have just suffered a critical blow. This is very unfortunate because string theory has a near-monopoly in the field of theoretical high-energy physics, and as with anything else, a monopoly is never good. The evidence against the linear order model of LQG comes from a recent paper from the Large High Altitude Air Shower Observatory (LHAASO) experiment.
Find the paper here arxiv.org/abs/2402.06009
Or here: journals.aps.org/prl/abstract/10.1103/PhysRevLett.133.071501
The authors claim: "We use this unique observation to place stringent
constraints on an energy dependence of the speed of light in vacuum, a manifestation of Lorentz invariance violation (LIV) predicted by some quantum gravity (QG) theories. Our results show that the 95% confidence level lower limits on the QG energy scales are EQG,1 -10 times of the Planck energy EPl for the linear and the quadratic LIV effects, respectively. Our limits on the quadratic LIV case improve previous best bounds by factors of 5–7."
Lorentz invariance, the fundamental symmetry of Einstein’s relativity, has withstood strict tests over the past century . However, deviations from Lorentz invariance at energies approaching the Planck scale are predicted in many quantum gravity (QG) theories seeking to unify quantum theory and general relativity. Although any signals of Lorentz invariance violation (LIV) are expected to be very tiny at attainable energies EPl, they can increase with energy and accumulate to detectable levels over large propagation distances.
Previous constraints on LIV are found from the FERMI space telescope in 2009: journals.aps.org/prd/abstract/10.1103/PhysRevD.99.083009
symmetrymagazine.org/breaking/2009/10/28/gamma-ray-burst-restricts-ways-to-beat-einstein%25e2%2580%2599s-relativity?language_content_entity=und which concludes "Meanwhile, loop quantum gravity had a class of ideas that have now been ruled out."
In this deep dive, I unpack the significance of LQG, its implications for unifying quantum mechanics with general relativity, and the potential blow it recently suffered this is one such model considered. I also reflect on the broader implications for theoretical physicists like Carlo Rovelli, Eric Weinstein, Stephen Wolfram and others if string theory remains unchallenged. Lastly, obviously this is one such model considered, and other versions of LQG could still survive to fight another day.
See my other video about LQG: youtu.be/-6A6myur--c
Key Takeaways:
00:00 Intro
02:11 What is loop quantum gravity (LQG)?
06:26 New evidence from the Lasso team challenges LQG predictions
09:15 String theory vs. loop quantum gravity
10:54 Outro
Additional resources:
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Into the Impossible with Brian Keating is a podcast dedicated to all those who want to explore the universe within and beyond the known.
Make sure to subscribe so you never miss an episode!
#intotheimpossible #briankeating #loopquantumgravity
Join my mailing list briankeating.com/list to win a real 4 billion year old meteorite! All .edu emails in the USA 🇺🇸 will WIN!
Get early access to new videos (+ other perks): youtube.com/channel/UCmXH_moPhfkqCk6S3b9RWuw/join
Is loop quantum gravity wrong?
The leading contender to string theory, loop quantum gravity (LQG), may have just suffered a critical blow. This is very unfortunate because string theory has a near-monopoly in the field of theoretical high-energy physics, and as with anything else, a monopoly is never good. The evidence against the linear order model of LQG comes from a recent paper from the Large High Altitude Air Shower Observatory (LHAASO) experiment.
Find the paper here arxiv.org/abs/2402.06009
Or here: journals.aps.org/prl/abstract/10.1103/PhysRevLett.133.071501
The authors claim: "We use this unique observation to place stringent
constraints on an energy dependence of the speed of light in vacuum, a manifestation of Lorentz invariance violation (LIV) predicted by some quantum gravity (QG) theories. Our results show that the 95% confidence level lower limits on the QG energy scales are EQG,1 -10 times of the Planck energy EPl for the linear and the quadratic LIV effects, respectively. Our limits on the quadratic LIV case improve previous best bounds by factors of 5–7."
Lorentz invariance, the fundamental symmetry of Einstein’s relativity, has withstood strict tests over the past century . However, deviations from Lorentz invariance at energies approaching the Planck scale are predicted in many quantum gravity (QG) theories seeking to unify quantum theory and general relativity. Although any signals of Lorentz invariance violation (LIV) are expected to be very tiny at attainable energies EPl, they can increase with energy and accumulate to detectable levels over large propagation distances.
Previous constraints on LIV are found from the FERMI space telescope in 2009: journals.aps.org/prd/abstract/10.1103/PhysRevD.99.083009
symmetrymagazine.org/breaking/2009/10/28/gamma-ray-burst-restricts-ways-to-beat-einstein%25e2%2580%2599s-relativity?language_content_entity=und which concludes "Meanwhile, loop quantum gravity had a class of ideas that have now been ruled out."
In this deep dive, I unpack the significance of LQG, its implications for unifying quantum mechanics with general relativity, and the potential blow it recently suffered this is one such model considered. I also reflect on the broader implications for theoretical physicists like Carlo Rovelli, Eric Weinstein, Stephen Wolfram and others if string theory remains unchallenged. Lastly, obviously this is one such model considered, and other versions of LQG could still survive to fight another day.
See my other video about LQG: youtu.be/-6A6myur--c
Key Takeaways:
00:00 Intro
02:11 What is loop quantum gravity (LQG)?
06:26 New evidence from the Lasso team challenges LQG predictions
09:15 String theory vs. loop quantum gravity
10:54 Outro
Additional resources:
➡️ Follow me on your fav platforms:
✖️ Twitter: https://x.com/DrBrianKeating
🔔 YouTube: youtube.com/DrBrianKeating?sub_confirmation=1
📝 Join my mailing list: briankeating.com/list
✍️ Check out my blog: briankeating.com/cosmic-musings
🎙️ Follow my podcast: briankeating.com/podcast
✨ Member's only playlist: youtube.com/playlist?list=UUMOmXH_moPhfkqCk6S3b9RWuw
Into the Impossible with Brian Keating is a podcast dedicated to all those who want to explore the universe within and beyond the known.
Make sure to subscribe so you never miss an episode!
#intotheimpossible #briankeating #loopquantumgravity
