1. Gravity by Entropy Theory
Muhammad Shahrul Arif Bin Adi Rumi SIF160050
SIF3007 Elementary Particle Physics, Semester 1 Session 19/20
Instructor: Professor Dr. Wan Ahmad Tajuddin Bin Wan Abdullah
2. Introduction
• The theory states that entropy is considered as a repulsive force (pushing away order to disorder), while gravity is an attractive force
(pulling in disorder into order).
• This is a radical approach; meaning gravity is not a fundamental interaction but instead is emergent; a consequence of a physical
system of quantum disorder (this means relating gravity as a part of Grand Unified Theory is not the right approach !).
• This theory was proposed by E.Verlinde (2011), which developed the entropy idea from a work of Padmanabhan (2010).
Space and Entropy
• Consider the case; As space increases, number of possibilities for microstates Ω increases.
• Then entropy also increases by the relation S(x)=kBlog Ω(x) .
Entropy and Expanding Universe
• Cosmology states The Universe is accelerating and expanding, thus entropy also increases.
• Even though some matter may come close to each other and experiences gravity, the effective Newton’s Gravity decreases since
expanding Universe increase the distance between them.
Gravity and Entropy, Second Law of Thermodynamics and Equilibrium
• 2nd law of Thermo states entropy change dS≥0.
• As time moves until at equilibrium ds=0, gravity must also vanish to obey the law ! (Assuming The Universe is an isolated system)
Another possibility is that net gravity is equal to net entropy, but this seems out of reach since gravity is negligible as universe
expands.
• Then, this seems that gravity and entropy is the same thing and seems to be uni-directional in the time’s arrow. What if maximum
entropy is reached? Does time will move backwards and causes an “anti Big Bang”?
• If gravity is emergent, then so does space time geometry.
Conclusion
• For such a radical idea, it does receive a fair share of criticisms. Kobakhidze (2011) pointed out that this theory do not agree with results
of an experiment related to ultra-cold neutrons in the gravitational field of Earth.
• Also, the theory must fit itself within the frameworks of other models such as The Standard Model and QFT.
• Thus, this theory requires more tests and validation to prove its practicality. If it proves so, then gravity will come to an end as a
fundamental force.
Equation in black hole pointed by Verlinde. TH is
Hawking temperature, and SBH is Bekenstein Hawking
entropy.
3. Thank you.
References:
Kobakhidze, A. (2011). Gravity is not an entropic force. Physical Review D, 83(2), 021502.
Padmanabhan, T. (2010). Thermodynamical aspects of gravity: new insights. Reports on Progress in Physics, 73(4), 046901.
Verlinde, E. (2011). On the Origin of Gravity and the Laws of Newton. Journal of High Energy Physics, 2011(4), 29.
