Jonathan Oppenheim has an inclination to place bets, but they are not the commonplace kind most people are used to. As a quantum physicist at University College London, his wagers revolve around the basic structure of existence - and his latest one is on the very construct of space-time.
General relativity and quantum theory are two of the most important theories of physics and they are in conflict with each other. General relativity states that the force of gravity is due to mass distorting the space-time continuum, likened to a flexible sheet. Quantum theory, on the other hand, explains the world of particles and suggests that all matter and energy is composed of small, distinct units. Combining these theories would enable us to comprehend much of reality but the incompatible mathematics of quantum theory and the smooth character of space-time make this impossible.
Physicists have been attempting to "quantize" gravity for nearly a century in order to make it fit into the quantum mould, like the other three forces of nature. However, Oppenheim wonders if this might be the incorrect assumption, and so he made a 5000:1 bet that space-time is not ultimately quantum.
The New Scientist spoke with him to gain insight into his opinion on why the accepted opinion may be incorrect, which experiments could potentially provide answers, and why physicists find betting so appealing.
Is it reasonable to suggest that a majority of physicists view modifying general relativity as the most effective means of combining it with quantum theory?
Jonathan Oppenheim : It is widely believed that general relativity will eventually be a quantum theory. However, there is a division among those who study quantum theory, with some wanting to quantise everything, and a few who are less sure. In the relativity community, they take much time to contemplate time, which leads to more doubt when contemplating the quantisation of time due to the confusion it can cause.
It's hard to say what my opinion is on this issue. It's possible that the next theory of gravity won't be either quantum or classical physics. The inquiry then is: Will the next gravity theory be more closely related to quantum gravity or a changed classical theory? I believe it's important to be more cautious, as we could be making a serious error by putting all our trust in one idea.
What is it about time in particular that makes it so difficult to manage?
Quantum theory is generally seen as a description of events on a subatomic level that transpire over time. Time is treated as an invariable backdrop, and the quantum systems alter with respect to it. However, in general relativity, space-time itself is dynamic and can be distorted. If we quantify the rate at which time passes, then the fundamental structure that quantum theory requires is lost. It is tough to even discuss a moment in time, since it is impossible to discern which "segments" of space-time are in the future and which are in the past.
Tackling the underpinnings of quantum theory may be difficult, and the concept of time is still a mystery. Stripping away this theoretical framework is an immense challenge.
Why has the concept that gravity should be quantized become so widely accepted?
The notion that gravity should be quantised was prominent in the 1980s and may have even dated back to the late 1950s. Looking back, it is evident that the Chapel Hill conference of 1957 was a key event in the discussion surrounding this matter. A full record of it exists and it is very interesting to read; Richard Feynman and John Wheeler were among the physicists debating this question, with Feynman's arguments evidently convincing many of the researchers present that gravity needed to be made quantum.
When we take a second look at the debates, we have developed our comprehension of quantum theory. We have a better understanding of entanglement, where two particles distant from each other still exchange data, and the similarity between the classical probability distributions and quantum wave-functions, which provide the chances of what the properties of a quantum object would be when observed. Consequently, we are aware that it could be logical not to quantise gravity. Nevertheless, a certain point of view has already been established.
Physics is full of questions, but how significant is the inquiry into quantum gravity?
This is a significant topic to consider. Any inquiries concerning cosmology, the regular model of particle physics, or dark matter all relate to our particular universe. This universe consists of various particles and forces, which all follow the laws of quantum theories. Therefore, quantum theory should be understood as the structure that is used to comprehend our universe. Subsequently, the query of whether the laws of physics are completely quantum, a hybrid, or something else is a different level of inquiry. It is about the structure of natural laws; it is almost a metaphysical issue.
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