Cosmologists have been looking for only six numbers all their lives.

The universe on the largest scale and the earliest universe are actually quite simple, and their main features can be easily described by just a few special parameters. Compared with other things, such as the incomparably complex Earth, such as the atmosphere, oceans, moving continental plates, and magnetic fields, the former is much simpler, and its appearance can be clearly seen by listing a few main properties.

The previous paragraph is extracted from the new book "A short History of the Universe" by American physicist Lehmann Page. In his book, the famous cosmologist introduces us to today's scientists' understanding of the model of the universe and the direction they want to explore next. We also had the privilege of interviewing him and asking about something related to cosmology.

In fact, we have a more comprehensive understanding of the whole universe than the complex interaction mechanisms in the interior of the earth. In front of the vastness of the universe, a city, a planet, and even an entire galaxy will become insignificant fluctuations. Today, countless ground and space telescopes have provided us with too much evidence of the formation of the universe. With the help of these expensive and sophisticated instruments, astronomers have peeped into the earliest secrets of the universe, and even traced the first light in the universe-the cosmic microwave background.

All the evidence is summed up as a cosmic model with six main parameters, and behind the model is an increasingly perfect cosmological theory. The proportion of matter, dark matter and dark energy, the depth of light when the universe is reionized, the amplitude of the original power spectrum and the scalar index determine the fate of the whole universe. Although there are a lot of crazy theories and speculations, the theoretical predictions which are perfectly consistent with the observed facts all explain their correctness. Now, cosmologists have even begun to verify the secondary conclusions predicted by their theories, such as looking for gravitational waves from the Big Bang.

So, what kind of law does the universe follow to understand the answer to the question in detail? the first thing we have to do is Einstein's masterpiece, general relativity. But for most of us, it is too difficult to catch up with the genius of a hundred years ago. On the other hand, Lyman Page provides us with a different perspective in his new book, A short History of the Universe.

As one of the co-founding researchers of the Wilkinson Microwave Anisotropy detector (WMAP), it is a group of people represented by him who ushered in the era of accurate measurement of the universe. He will not directly tell the reader how old the universe is today and whether the universe is curved or straight, but he will tell you in the simplest language why and how we explore the answers to these questions. and then guide the reader step by step to deduce that attractive answer.

Lehmann Page: the cosmic microwave background was created when the universe was very young and hot. It is the earliest part of the universe that standard physics can trace back to. In the 40 years after the birth of the universe, atomic matter (charged protons and electrons) interacted closely with radiation. If you can "see" the universe at that time, you will find that you are standing on the surface of the sun and looking inside the sun. You can't see far away because the radiation is scattered by photons. You can only see the dazzling light, and the universe at that time seems to be surrounded by the sun.

The early universe was simple. The universe we see now is made up of all kinds of celestial bodies such as planets, stars, galaxies and galaxy clusters. There were no celestial bodies in the early universe, just a uniform mixture of radiation and different forms of atoms, a bit like a pot of cosmic soup. Importantly, there may be some minor changes in this cosmic soup, and the perturbation eventually evolves into the entire universe we see in the night sky.

Lehmann Page: cosmic microwave background radiation is the ideal frame of reference, similar to that formed by all extremely distant galaxies. Imagine you are staring at a swarm of bees next to a hive, two of which may circle the sun like the earth, but the whole colony is a stable reference for the location of the hive, and each bee knows its own movement relative to the hive.

Lehmann Page: yes! We can also learn a lot from the cosmic microwave background, and related research is still the best way to understand the early universe and the universe as a whole. It is generally believed that until our detection accuracy reaches the limit caused by interference from the nearby interstellar environment, we should all continue to move forward with the detection of the cosmic microwave background. For example, in some directions, the dust inside the Milky way will block our view, making it difficult for us to see what is going on outside the Milky way, but we have not yet reached this limit.

Lehmann Page: at a scale of about 25 million light-years, the universe is uniform. But we have also observed larger structures, and 25 million years is just an average.

Lehmann Page: I guess what you mean is that the anisotropy of the universe is higher than our current observation level. First of all, it shows that there is something we haven't detected! As far as I know, almost all anomalies are related to random fluctuations. One of them is often referred to as a hemispheric anomaly (hemispherical anomaly), which is too large to occur accidentally. That is to say, we have only one universe to observe, so it is difficult to objectively quantify what is normal.

Lehmann Page: no!

Lehmann Page: because the model is in good agreement with the observed data, and the model is earlier than the data. All kinds of experiments can measure the universe, but only this model can match all the observed data for several key parameters. Now that our observations have entered a new stage, we begin to measure the secondary effects of the model, such as the gravitational lens of the cosmic microwave background, which is also consistent with the prediction of the model. Like most of my colleagues, we really want to find something that goes against the model, and that's how we advance science.

Lehmann Page: models like those proposed by Scordis and Zelicher are very important to further consolidate the standard model and point out new things for us. They modified the model to match the observed data, which is a defect compared to the cold dark matter model. Importantly, however, they predicted the polarization of the cosmic microwave background, which can be tested. There are other tests at the galactic scale, such models (MOND theory) replace the dark matter theory with corrections to gravity.

Lehmann Page: after I left work in the field of cosmic microwave background, I devoted myself to axon detection. Axion is a candidate of dark matter and a substitute for weakly interacting high-mass particles. My choice has made my opinion clear. We know that dark matter must exist, and weakly interacting massive particles may be very attractive because some candidate particles seem very reasonable and seem to occur naturally in the early universe. However, current measurements have ruled out many models of weakly interacting massive particles, but there are still some possibilities for dark matter, and we don't know if we can detect them in the laboratory.

Lehmann Page: in my opinion, the latest major change is the observation that the expansion of the universe is accelerating. After that, we can use a simple six-parameter model to describe almost all cosmological observations. Looking ahead, if we find gravitational waves from the Big Bang, it will be the next revolutionary achievement. We may also find that the Hubble constant is contrary to our expectations