The 'science' lecture prepared for undergraduate students majoring in 'humanities and social sciences' at Harvard University was born as 'Science Class for Harvard Liberal Arts Students'.
As a course for students who are not majoring in science, this book, which takes the form of an introductory course, broadly examines the process by which humans have explored the natural world from ancient times to the present under the three major themes of space, Earth, and life.
The fact that the Earth orbits the Sun, that continents move, and that life has evolved may seem obvious at first glance based on today's knowledge, but when it was first discovered, it was a profound, world-changing insight.
The process of discovery was not smooth either, and scientists who jumped into solving nature's puzzles sometimes ended up wandering in the wrong direction or making the wrong choices, leaving behind a dark history of reaching dead ends.
"Science Class for Harvard Liberal Arts Students" follows this journey of inquiry, showing that science is not a complete knowledge but a process of continuous observation, questioning, and proof.
Additionally, the importance of asking questions is emphasized throughout the class.
Because science begins with a question, leads to exploration, reaches understanding, and then moves further with another question.
You can't learn everything about science in a one-semester introductory course.
But as we follow the scientific journey of observing natural phenomena, wondering how they work, and thinking based on evidence, our understanding of not only science but also the world expands.

Science often seems like magic, but there is a big difference between science and magic, and between scientists and magicians.
Scientists are always willing and eager to talk about their research and discoveries in detail.
So perhaps I will babble endlessly, as I do in this book.
But the magician is the exact opposite.
The magician also demonstrates like I do in this book.
Now, I just put three pieces of colored cloth tied together in front of you into my pocket.
Then he recited the appropriate spell and took another piece of cloth out of his pocket.
Ta-da! All the fabrics that were tied together are now untied.
But I don't explain anything.
The magician uses his voice only to recite spells quickly.
By oath, they never reveal what tricks they have used to anyone other than fellow magicians.
They will take this secret to their graves, and so we eventually return to science.
--- From "Introductory Remarks"

The primary purpose of science is not to find out why, but to study the behavior of nature and build appropriate models.
For what purpose, and for what reason? Beyond satisfying humanity's innate curiosity, there was a far more practical purpose.
The most important of these is food.
When is the best time to plant crops? When is the best time to go hunting? And when, exactly, do you need to know the answers to these questions? --- Chapter 1.
From "Light Moving in the Sky"

Strictly speaking, Kepler's laws are not laws in the sense that they cannot be broken.
However, it provided a fairly good approximation to the behavior of nature, especially given the level of observation available in the early 1600s.
In particular, the predictions are in fairly good agreement with Tycho's records of observing the positions of the planets.
One important example is that when applied simultaneously to both Earth and Mars, the errors in predicting retrograde motion that had plagued past models disappeared without a trace.
Kepler's innovations marked a significant milestone in the development of modern science.
His law was independently posited and did not follow any other simple principle, but it was a great step forward.
From a modern perspective, this law may seem like a crude, ad hoc model, but as mentioned earlier, it was a remarkable leap forward in raising the level of modeling to the level of measurements available at the time, the first advance in 1,500 years of human effort to create a quantitative model of planetary motion.
--- Chapter 2.
From “Models of Celestial Motion”

Returning to Edwin Hubble, he estimated its distance to be millions of light-years based on observations of Cepheid variables in distant galaxies.
This was possible thanks to the use of much more powerful telescopes than ever before.
Hubble's results showed that the island universe was farther away than what was then believed to be the boundary of our galaxy, and led to the conclusion that it was a separate galaxy from our own, changing the course of astronomy.
In this way, our sense of superiority over our privileged position in the universe was further diminished, and we were confirmed to be far away from even the center of a single galaxy.
Finding definitive evidence that intelligent life exists somewhere in the universe would be the next and final step in dismantling the old belief that we occupy a privileged position in the universe.
--- Chapter 5.
From "Space Distance Ladder"

The discovery of the CMB (cosmic microwave background) is valuable in that it provides a solid observational foundation for the field of cosmology, which was previously purely speculative.
In fact, cosmology is the field that studies the origin and subsequent development of the universe on the largest spatial and temporal scales, ultimately drawing the 'big picture'.
Furthermore, many subsequent observations and theoretical studies of the CMB have transformed cosmology into a data-driven, cutting-edge field of astronomy, and indeed one that allows us to think about our origins on the largest scale possible.
--- Chapter 6.
From "Cosmic Microwave Background Radiation"

The important question here.
Does the fracking process itself cause earthquakes? Or is the process of pumping wastewater back into the ground the direct cause? (...) The answer to this question is of practical importance.
If fracking itself is the cause, then it should be banned.
Conversely, if wastewater is the cause, a solution can be found by changing the treatment method.
(……) One thing is certain: fracking clearly demonstrates that human activities can have a direct impact on the Earth's environment.
This issue also serves as an example of how citizens' voices can be reflected in policy, highlighting the importance of having even a minimal understanding of social issues related to science.
Of course, this isn't always the case, but having some background knowledge will help you make smarter choices.
--- Chapter 9.
From "Exploring the Earth's Interior and Earthquakes"

Based on these calculations, and taking into account some of the uncertainties inherent in these assumptions, Kelvin concluded in the early 1860s that the Earth was between about 40 million and 100 million years old.
Geologists, on the other hand, believed that the Earth was much older than that, but had no way to verify it, so they were paralyzed by Kelvin's quantitative approach.
Of course, there are skeptics who eloquently argue against the claims, but it is important to remember that scientific disputes should be resolved with evidence, not words.
--- 「Chapter 12.
From "The Age of the Earth"

So, the total length of DNA that a person has is the product of the length of DNA in one cell and the total number of cells, which is approximately 10 to the 14th square meter, and if this value is converted to astronomical units, it is 700 AU.
This length is equivalent to the diameter of the entire solar system.
Going a step further, if we calculate the total length of DNA of the 8 billion people living on Earth, it would be about 75 million light-years, more than 1,000 times the diameter of our galaxy.

--- Chapter 19.
From “Genetic Information and the Central Principle of Life”