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The conflict between gravity and quantum mechanics: How to solve this cosmic problem?
In the field of physics, there is a passion for exploring the Theory of Everything (TOE)—a theory that can uniformly describe all physical phenomena in the universe. This exciting but arduous pursuit faces a confrontation between two flagship theories: general relativity and quantum mechanics. These two theories are like the two pillars of the universe, able to explain the operation of the macroscopic and microscopic worlds respectively. However, under certain extreme conditions, they appear to be unable to coexist harmoniously.
"A theory of everything should be able to describe all physical phenomena in the universe in principle."
General relativity, proposed by Einstein, is the theoretical framework for understanding the effects of gravity. It focuses on describing large-scale phenomena (such as planets, interstellar and universe), and explains how curved space-time affects the movement of matter. In contrast, quantum mechanics focuses on the behavior of the microscopic world, mainly involving three basic interactions that do not include gravity: the strong nuclear force, the weak nuclear force, and the electromagnetic force.
In the academic dialogue between the two, the success of quantum mechanics links the operating modes of elementary particles, while general relativity provides a more macroscopic perspective, such as the structure and evolution of the universe. However, contemporary science faces a contradiction that cannot be ignored: under extreme conditions at the Planck scale (such as the center of a black hole or the early days of the Big Bang), the rules of these two theories no longer seem to apply.
"The two theories are considered to be incompatible at extremely small scales."
Such contradictions have prompted scientists to continually search for in-depth frameworks that could unify the two theories. As a result, quantum gravity has become one of the hottest areas of research, examples include string theory. String theory attempts to describe all particles in the universe with a set of the most basic strings, which form the various particles we observe based on their different vibration modes.
However, the development of string theory has not always been smooth sailing. Its most significant flaw is the lack of experimental testing methods, which has triggered heated and sometimes controversial debates in the scientific community. String theory presupposes that during a very short period of time at the beginning of the universe, the four fundamental forces were actually a single fundamental force. This theory requires six or seven dimensions of spacetime, in addition to the four we are familiar with.
"The multi-dimensional view of the universe proposed by string theory seems to be contrary to our intuition."
In order to explain the multidimensionality of cosmic objects and how gravity combines with other fundamental effects, the development of this theory needed to address the problem of transgressions between elementary particles and large-scale phenomena. Although string theory has attracted many eager physicists, there are still voices of doubt within the scientific community about its validity and predictive power.
At the same time, loop quantum gravity serves as another competing theory that attempts to fundamentally provide an alternative theory to quantum gravity. It focuses on the quantum properties of space-time itself, and may provide a stronger foundation for future "theories of everything." These theories also face challenges that require overturning traditional ideas and redefining the relationship between particles and space-time.
"Any effort to explore the theory of everything may change our fundamental understanding of the universe."
In the context of this huge scientific discussion, we can't help but ask, can these pursuits that mix theory and experiment ultimately help us understand the fundamental operating principles of the universe? Will stereotypes as we understand them today be overturned by new theories? This may be a question worth pondering for all of us?
