質子衰變，這一曾是“大統一理論”（GUTs）在20世紀70年代末80年代初的預測之一，近年來再次引發了物理學界的廣泛討論。不同於電子和中子的穩定性，質子作為原子核的核心，是否會在某一天衰變成其他粒子，一直是基礎物理學的一個懸而未決的問題。現如今，實驗結果已經將質子衰變的壽命限制在了10^34年左右，遠遠超出了宇宙的年齡。

However, it is worth noting that the experimentally set "proton decay lifetime" is based on the results of the Earth experimental environment and the background of modern physics. But physicists are beginning to question whether such results can be applied to other parts of the universe, or even to different time scales. To put it simply, do the properties of proton decay change depending on space and time?

Peter Denton and Hooman Davoudiasl of Brookhaven National Laboratory offer new perspectives. They propose,If it is assumed that protons do decay, then the decay rate may vary greatly from one cosmic environment to another.Specifically, they considered two extreme environments—Earth's iron core—and neutron stars—to speculate on the decay lifetime of protons in these places.

Theoretically, the decay process of protons may take many forms, and one of the possible decay channels is the decay of protons into a positive meson and a dark matter fermion. As the name suggests, these particles barely interact with particles in the Standard Model, making them difficult to observe directly in experiments. If the decay process involves this dark matter fermion, and the mass of this fermion is less than the mass of the proton minus the mass of the positive meson, then the decay process of the proton may be much faster than that observed experimentally.

However, this is only a starting point, and the complexity of the problem is far beyond what this model can cover. For example, if the decay rate of protons is really affected by space and time, how do we define the decay lifetime? Proton lifetimes of more than 34^0 years seem long enough for experiments on Earth to be negligible, but does this criterion still hold true elsewhere or at other times?

以地球的鐵核為例，登頓和達武迪亞斯爾的研究表明，假如質子的衰變速率比實驗觀測到的要快得多，它可能產生的熱量會直接影響地球內核的狀態。地球內核之所以保持固態，部分原因在於它的溫度沒有達到足以將其熔化的臨界值。如果質子的衰變速率過快，產生的熱量會導致內核過熱，進而改變地球的地質結構。然而，目前我們並未觀察到這種情況發生。根據他們的計算，若質子的衰變速率達到預期的加速水準，那麼地球的鐵核已經應該在約20億年前完全熔化，而這一結果與地質學家的估算顯然不符。因此，他們的推理表明，質子的衰變壽命至少大於2×10^18年。

A further idea expands the horizon from Earth to other cosmic bodies, especially neutron stars. Neutron stars have extremely low ambient temperatures and a limited age, and scientists speculate that they could be an important window into proton decay. Denton and Davout Assr found that proton decay lifetimes also have a crucial effect on the heat production of neutron stars. If the decay rate of protons is too fast, the star will behave abnormally due to the accumulation of heat that does not conform to the current physical model. Through these analyses, they further speculated that the proton decay lifetime must be greater than 18.0×0^0 years, and this estimate is close to the estimated value of the kernel heat model.

Of course, the study of proton decay is not limited to this theoretical derivation. For studies on longer time scales, physicists have also proposed the hypothesis of "ancient detectors". The idea came from the study of the moon's minerals. Assuming that the decay of protons can have an impact on nature on very long time scales, it may be possible to find traces of decay by taking olivine samples at a depth of several kilometers below the moon. The experimental design of this "ancient probe" is not only a further verification of the proton decay problem, but also provides us with an opportunity to observe the time scale spanning billions of years or more.

Although these discussions may seem distant, they are closely related to our understanding of the basic structure of matter. From the model of proton decay, we can not only reflect on whether the grand unified theory can accurately describe the laws of nature, but also get a glimpse of the underlying laws in the evolution of the universe. After all, if proton decay exists, and this decay rate varies in different times and spaces, it will undoubtedly become a "fingerprint" of new laws of physics, helping us decipher more secrets of the universe.