Is Gravity Quantum?

[Guest]

FYI: 'Is Gravity Quantum?
The ongoing search for the graviton—the proposed fundamental particle carrying gravitational force—is a crucial step in physicists’ long journey toward a theory of everything.'

https://www.scientificamerican.com/article/is-gravity-quantum/.

[Guest]

FYI: 'Quantum spacetime':

"In mathematical physics, the concept of quantum spacetime is a generalization of the usual concept of spacetime in which some variables that ordinarily commute are assumed not to commute and form a different Lie algebra. The choice of that algebra still varies from theory to theory. As a result of this change some variables that are usually continuous may become discrete. Often only such discrete variables are called "quantized"; usage varies..."

Source Link: https://en.wikipedia.org/wiki/Quantum_spacetime.

[Guest]

"It (mathematics) seems that it fails to describe quantum gravity." -- Prof. N. S. Duxbury.

"If quantum gravity exists, then we, mathematicians, will eventually model/understand it mathematically." -- Dave.

Go Blue!

[Guest]

"We must know. We will know!" -- David Hilbert.

[Guest]

FYI: 'Quantum Gravity',

http://www.issp.ac.ru/ebooks/books/open/Quantum_Gravity.pdf.

[Guest]

Good Reference Book: 'GEOMETRY, TOPOLOGY, AND PHYSICS, 2ed.' by Prof. MIKIO NAKAHARA.

[Guest]

FYI: 'Quantum Gravity and Quantum Cosmology', by Prof. J. Hartle,

https://www.youtube.com/watch?v=xcJ7diTtURc.

Enjoy!

[Guest]

"It (mathematics) seems that it fails to describe quantum gravity." -- Prof. N. S. Duxbury.

"If quantum gravity exists, then we, mathematicians, will eventually model/understand it mathematically." -- Dave.

Go Blue!

FYI: 'How To Test Quantum Gravity', by Prof. S. Hossenfelder,

"Einstein's theory of gravity, General Relativity, is awesome. But strictly speaking, it is wrong. We know that because it cannot handle the quantum behavior that particles have. To make quantum theory compatible with General Relativity, we need a theory of quantum gravity. We still don't have one. In this video, I explain what possibilities we have to experimentally test quantum gravity..."

Source Link: https://www.youtube.com/watch?v=HKtFU2Pxnm0;

Relevant Paper: 'A micromechanical proof-of-principle experiment for measuring the gravitational force of milligram masses', by Prof. J. Schmöle et al.,

https://iopscience.iop.org/article/10.1088/0264-9381/33/12/125031/pdf.

Enjoy!

[Guest]

Old Remark: Often Nature works to achieve its evolutionary goals in an optimal way. So, scientists must prove or show quantum gravity makes sense.

And the detection of quantum gravity is paramount.

General Questions: How do things work in Nature? Why?

[Guest]

A Relevant Idea: 'A brief history of minimal surfaces and the ants that love them',

https://phys.org/news/2021-11-history-minimal-surfaces-ants.html.

[Guest]

Old Remark: Often Nature works to achieve its evolutionary goals in an optimal way. So, scientists must prove or show quantum gravity makes sense.

And the detection of quantum gravity is paramount.

General Questions: How do things work in Nature? Why?

The more mathematics one can absorb (understand) the better. And it is best to have a problem/project at hand when studying mathematical theory since theory and practice (application) are mutually beneficial. Amen!

The quest to discover the existence of quantum gravity and to model it mathematically is a grand impetus to study and apply some advanced mathematical knowledge/theories. Good Luck!

[Guest]

Keywords: Dynamic Manifolds, Networks, and Conservation Laws

Question: How are energy, physical field theories, entropy, quantum physics, and gravity related?

[Guest]

FYI: 'Exploring quantum gravity and entanglement using pendulums',

https://phys.org/news/2021-09-exploring-quantum-gravity-entanglement-pendulums.html.

[Guest]

FYI: 'Field (physics)', https://en.wikipedia.org/wiki/Field_(physics);

'This Is Why Quantum Field Theory Is More Fundamental Than Quantum Mechanics',

https://www.forbes.com/sites/startswithabang/2019/04/25/this-is-why-quantum-field-theory-is-more-fundamental-than-quantum-mechanics/?sh=60edbfac2083.

[Guest]

FYI: 'Unifying Gravity and Electromagnetism: 2021 Meeting of the Division of Particles and Fields of the American Physical Society (DPF21)'

https://indico.cern.ch/event/1034469/contributions/4426793/.

[Guest]

WOW! (Words Of Wisdom!):

"The idea is that when you can teach something in the simplest way possible, you will master it.". -- Richard Feynman.

Source Link:

https://www.businessinsider.com/nobel-prize-winning-technique-to-learn-anything-quickly-and-effectively-2021-12?utm_source=copy-link&utm_medium=referral&utm_content=topbar

[Guest]

FYI (Link to Relevant Question & Answer):

It's energy and not the so-called spacetime that matters most on how gravity and the universe works, right?

[Guest]

What makes matter seek the lowest energy levels? Does that suggest that gravity must be quantized at micro scales?

“You're asking a very insightful question that gets to the heart of a major unsolved problem in physics. Let's break it down:

**What makes matter seek lowest energy levels?**

As explained before, this is due to a combination of:

* **Thermodynamics:** The tendency towards higher entropy, which often correlates with lower energy states.

* **Quantum Mechanics:** The probabilistic nature of particles, favoring lower energy states due to the Boltzmann distribution and the stability of ground states.

* **Fundamental Forces:** The forces that govern interactions between particles, driving them towards configurations that minimize potential energy.

**Does that suggest that gravity must be quantized at micro scales?**

Here's where it gets interesting:

* **The Connection:** The fact that *all* other fundamental forces (electromagnetic, strong, and weak) are quantized at the micro scale strongly suggests that gravity should be too. The consistent behavior of matter seeking lowest energy levels across all interactions hints at a unified underlying principle.

* **The Problem:** However, gravity, as described by General Relativity, is fundamentally different. It's a theory of spacetime curvature, not a quantum field theory like the others.

* **The Need for Unification:** To reconcile this, we need a theory of quantum gravity that can explain how gravity behaves at the quantum level.

* **The Implications:** If gravity is indeed quantized, it would mean that:

* Spacetime itself might be quantized, meaning it's made up of discrete units.

* Gravity would be mediated by particles (gravitons).

* The laws of gravity would need to be modified at very small scales.

**Why the "lowest energy" idea strengthens the case for quantum gravity:**

* The "lowest energy" principle is a universal observation. If other forces follow quantum rules to achieve this, it's highly improbable that gravity would be an exception.

* The current classical description of gravity doesn't readily explain how it would fit into this universal pattern of energy minimization at the quantum level.

* The fact that quantum fields are responsible for the other forces, and that all of those forces interact with matter that seeks the lowest energy state, implies that gravity must also be a quantum field.

**In essence:**

While the tendency of matter to seek lowest energy levels doesn't *prove* that gravity is quantized, it provides strong circumstantial evidence. It reinforces the idea that there's a fundamental unity to the laws of physics and that gravity should be part of the quantum world. The search for a theory of quantum gravity is driven by this very intuition.” —Gemini (AI chatbot)

Google’s AI Overview:

“Matter seeks the lowest energy levels because a system with lower energy is inherently more stable, meaning it is less likely to change or undergo further reactions; this is a fundamental principle in physics, where stability is associated with a minimum energy state. While this principle does not directly prove gravity needs to be quantized at micro scales, the idea of quantizing gravity is often explored in the pursuit of a unified theory that seamlessly integrates quantum mechanics with gravity, where the very nature of space-time at the smallest scales could be quantized.

Key points to consider:

Stability and energy: Systems naturally tend towards the lowest energy configuration because it represents the most stable state, similar to how a ball naturally rolls downhill to reach the lowest point on a slope.
Quantum mechanics and energy levels: In quantum mechanics, energy levels are quantized, meaning particles can only occupy certain discrete energy states. Atoms, for example, will naturally transition to their lowest energy level, called the ground state, where their electrons are in the most stable arrangement.
Gravity and quantization: While the idea of quantizing gravity is not directly proven by the tendency of matter to seek low energy levels, it is a topic of active research in the field of quantum gravity, as it could provide a more complete understanding of gravity at very small scales.“

Relevant Reference Link:

Scientists closer to finding quantum gravity theory after measuring gravity on microscopic level

David Cole

[Guest]

"Moreover, you're touching upon some deep and fascinating questions at the heart of physics! Let's break down the tendency of matter to seek lower energy states, and its implications for gravity and Hawking radiation:

**Why Matter Seeks Lowest Energy Levels:**

* **Thermodynamics and Entropy:**
* Systems naturally tend towards states of higher entropy (disorder).
* Lower energy states are often more stable and disordered, requiring less energy to maintain.
* This is related to the second law of thermodynamics.
* **Quantum Mechanics:**
* In quantum mechanics, particles occupy quantized energy levels.
* Transitions between these levels release or absorb energy.
* Particles naturally "decay" or transition to lower energy levels, releasing energy in the process (e.g., photons).
* **Minimization of Potential Energy:**
* Systems tend to minimize their potential energy.
* For example, a ball rolls downhill to reach a lower gravitational potential energy state.
* At the atomic level, electrons arrange themselves to minimize the electromagnetic potential energy.

**Gravity and Quantization:**

* **The Problem of Quantum Gravity:**
* Currently, gravity is described by Einstein's general relativity, a classical theory.
* Quantum mechanics describes the other fundamental forces (electromagnetic, strong, weak) at the quantum level.
* Reconciling these two frameworks into a theory of quantum gravity is a major challenge.
* **Implications of Matter Seeking Low Energy:**
* The tendency of matter to seek low energy states suggests that gravity, like other forces, might be quantized at micro scales.
* If gravity were not quantized, it would be difficult to explain how matter consistently reaches stable, low-energy configurations.
* **Hawking Radiation:**
* Hawking radiation arises from quantum effects near black hole event horizons.
* It suggests that black holes emit thermal radiation, implying a connection between gravity, quantum mechanics, and thermodynamics.
* Hawking's theory supports the idea that gravity has quantum aspects.
* **Quantum fluctuations:**
* Hawking radiation is caused by Quantum fluctuations near the event horizon of a black hole. These fluctuations cause particle/antiparticle pairs to pop into existance. Sometimes one of these pairs falls into the black hole, and the other escapes. This escaping particle is the Hawking radiation.
* **Theoretical Approaches:**
* String theory and loop quantum gravity are two leading candidates for a theory of quantum gravity.
* These theories attempt to quantize gravity by describing it in terms of fundamental particles or discrete spacetime structures.

**In summary:**

* The tendency of matter to seek low energy states is a fundamental principle in physics.
* This tendency, along with phenomena like Hawking radiation, suggests that gravity likely has quantum aspects.
* However, a complete theory of quantum gravity remains elusive.". -- Gemini AI chatbot

[Guest]

"The existence of gravitational waves **strongly suggests** the existence of the graviton, but it **doesn't definitively prove** its existence in the same way direct detection of a particle would. Here's why:

**Arguments for Gravitational Waves Strongly Suggesting Gravitons:**

* **Analogy to Electromagnetism:** Our most successful theory of gravity, General Relativity (GR), has a mathematical structure that shares similarities with electromagnetism (described by Quantum Electrodynamics, QED). In electromagnetism, accelerated charged particles produce electromagnetic waves (light), which are quantized as photons, the force carriers of the electromagnetic force. By analogy, accelerated masses (or more precisely, time-varying mass distributions) produce gravitational waves, suggesting a quantized carrier particle for the gravitational force: the graviton.
* **Field Theory Framework:** GR can be formulated as a classical field theory. Just as classical electromagnetic fields have a quantum counterpart (photons as excitations of the electromagnetic field), it's natural to expect that the classical gravitational field also has a quantum counterpart (gravitons as excitations of the gravitational field). Gravitational waves would then be macroscopic manifestations of these graviton excitations propagating through spacetime.
* **Energy Quantization:** Gravitational waves carry energy and momentum. If gravity is quantized, then this energy and momentum should ultimately be carried in discrete packets – the gravitons. While we measure the bulk energy and momentum of the waves, their quantized nature at the fundamental level implies the existence of these energy quanta.
* **Predictions of Quantum Gravity Theories:** Various theoretical approaches to quantum gravity (though not yet experimentally verified) predict the existence of the graviton as a massless, spin-2 particle that mediates the gravitational force. Gravitational waves fit naturally into these theoretical frameworks as classical limits of graviton interactions.

**Why Gravitational Waves Don't Constitute Definitive Proof of the Graviton:**

* **Classical Phenomenon Observed:** Gravitational waves, as detected by LIGO and Virgo, are currently observed as classical phenomena described by Einstein's field equations. While their existence is a profound confirmation of GR, the measurements so far haven't directly detected the quantization of the gravitational field or individual gravitons.
* **Scale of Detection:** Detecting individual gravitons is incredibly challenging due to the weakness of the gravitational force. The current generation of gravitational wave detectors is sensitive to the coherent, macroscopic effects of many gravitons (or the classical wave itself), not the individual quanta.
* **Alternative Explanations (Less Likely):** While highly improbable, it's theoretically conceivable (though no compelling alternative theories currently exist) that gravitational waves could arise from a quantized theory of gravity that doesn't involve a particle mediator in the same way as the other fundamental forces. However, such a theory would need to reproduce the successes of GR at classical scales and explain the wave phenomenon.
* **Quantum Gravity is Incomplete:** We don't yet have a complete and universally accepted theory of quantum gravity. While the graviton is a feature of many candidate theories, the details of its interactions and how it gives rise to classical gravity and gravitational waves are still under investigation.

**In Conclusion:**

The detection of gravitational waves provides extremely compelling indirect evidence for the existence of the graviton. They are the natural wave-like prediction of a field theory of gravity, analogous to light in electromagnetism. However, without direct detection of individual gravitons or definitive proof of the quantization of the gravitational field at the quantum level, the existence of gravitational waves alone doesn't constitute absolute, irrefutable proof of the graviton. It is, however, a very strong and important piece of the puzzle in our quest to understand the quantum nature of gravity."--Gemini AI chatbot