Why do we need a quantum theory of gravity? What would it do?

Click For Summary

Discussion Overview

The discussion centers on the necessity of a quantum theory of gravity and its potential implications for unifying quantum mechanics and general relativity. Participants explore the compatibility issues between these two foundational theories, particularly in extreme conditions such as black holes.

Discussion Character

  • Debate/contested
  • Exploratory
  • Conceptual clarification

Main Points Raised

  • Some participants propose that the goal of a quantum theory of gravity is to achieve a "theory of everything" that unifies quantum mechanics and general relativity.
  • Others argue that the incompatibility of quantum mechanics and general relativity is evident in scenarios where both must apply simultaneously, such as inside black holes.
  • A participant emphasizes that for a complete understanding of the universe, both theories must be applicable everywhere and at all times, suggesting that their current incompatibility indicates a fundamental incompleteness in our understanding.
  • Some express skepticism about whether a complete understanding of the universe is achievable, while others maintain optimism that it is possible, albeit with significant challenges.
  • Participants discuss the mathematical incompatibility of the two theories, particularly in the context of black holes, where the extreme conditions challenge the applicability of both theories.
  • String theory is mentioned as one of the proposed approaches to unify the different forces described by quantum mechanics and relativity.

Areas of Agreement / Disagreement

Participants express a range of views on the compatibility of quantum mechanics and general relativity, with some believing that a unifying theory is achievable and others expressing doubt about the possibility of fully understanding the universe. There is no consensus on the resolution of these issues.

Contextual Notes

Participants highlight the limitations of current theories in extreme conditions and the unresolved nature of the mathematical frameworks involved. The discussion reflects ongoing uncertainties and assumptions regarding the future of theoretical physics.

chaoseverlasting
Messages
1,050
Reaction score
3
Why do we need a quantum theory of gravity? What would it do?
 
Physics news on Phys.org
Where both quantum theory and general relativity must apply at the same time, they can't. Example - what goes on inside a black hole?
 
mathman said:
Where both quantum theory and general relativity must apply at the same time, they can't. Example - what goes on inside a black hole?
Well, "where [they] must apply at the same time" is understating the problem. To claim we understand our universe, they must be applicable at the same time EVERYWHERE and EVERYWHEN. Otherwise, our understanding is fundamentally incomplete.

Two of the greatest scientific theories in the history of civilsation - turn out to be incompatible. They can't both be right. Yet, they are each one of the best-confirmed theories in history.
 
Last edited:
Wow. What makes them incompatible?
 
DaveC426913 said:
Well, "where [they] must apply at the same time" is understating the problem. To claim we understand our universe, they must be applicable at the same time EVERYWHERE and EVERYWHEN. Otherwise, our understanding is fundamentally incomplete.

I don't think we will ever really understand our universe.
 
I think we'll get it. It may take a while, but I definitely think we'll get it... if we don't destroy ourselves in the process...
 
Quantum mechanics describes the actions and interactions of the extremely small, the particle level. Relativity describes massives amounts of matter, planets, stars, and such. They both are highly accurate as was mentioned, but when they are both applied to the same body/particle, they seem to fall apart. Why exactly?

I'm not 100% but it's the mathematics of them that does not lend itself to be compatible. As was mentioned with black holes, it's a huge amount of mass, but a terribly small, point-like structure.

Think of black holes almost as, what happens when both theories collide, and do we know exactly what goes on at the singularity? Nope.

The modern quest of physics is what is called a TOE (theory of everything) in which everything can be described in one ecompassing theory. Quantum Mechanics describes 3 forces (Nuclear Strong and Weak, and Electromagnetism) while relativity describes Gravity. When we are able to combine all of these into one theory, we will hopefully accomplish that.

One of these proposed theories is String Theory.

A very good question you asked, and i hope i am right and have clarified a little.

Good luck! =)
 
chaoseverlasting said:
I think we'll get it. It may take a while, but I definitely think we'll get it... if we don't destroy ourselves in the process...

No i don't think we'll never know/learn every knook and crany in our universe. To learn everything would take forever.
 
  • #10
Well, who can predict the future? It's useless to debate about this.
 
  • #11
no one can but i don't think we can learn everything the universe has to offer
 
  • #12
Thanks doug. very helpful post
 
  • #13
your welcome, i try =) ha
 

Similar threads

Undergrad What Are the Key Questions and Challenges in Understanding Quantum Gravity?
  • · Replies 5 ·
Replies
5
Views
2K
Graduate Loop Quantum gravity or String theory?
  • · Replies 10 ·
Replies
10
Views
5K
Graduate Gravity Measured with Milligram masses
  • · Replies 3 ·
Replies
3
Views
1K
High School Quantum Field Theory As Simple As Possible
  • · Replies 2 ·
Replies
2
Views
1K
Undergrad Is there some agreement on properties of a theory of quantum gravity?
  • · Replies 2 ·
Replies
2
Views
1K
High School Is gravitized quanta the solution rather than quantum gravity?
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad What are anomalies in quantum field theory?
  • · Replies 4 ·
Replies
4
Views
2K
High School Why is gravity a weak force at the atomic scale?
  • · Replies 8 ·
Replies
8
Views
1K
Graduate What exactly does 'Locality' in Gauge Theory mean?
  • · Replies 5 ·
Replies
5
Views
2K
Undergrad Why is Quantum Gravity theory still not "finished"?
  • · Replies 44 ·
2
Replies
44
Views
6K