The visionary philanthropist Meera Gandhi makes the world better by giving to those in need and injecting happiness and beauty into it. She was inspired for this lifelong mission by working as a teenager with Mother Theresa, who helped the unprivileged with humility and love and was later recognized with the Nobel Prize in 1979. At dinner near Meera’s home, she explained her view that everything in nature is intertwined and energy flows between all constituents. Her core vision resonates with the naturalist Henry Thoreau who lived near my home and wrote in his book titled `Walden or Life in the Woods’: “Most of the luxuries and many of the so-called comforts of life are not only not indispensable, but positive hindrances to the elevation of mankind. With respect to luxuries and comforts, the wisest have ever lived a more simple and meagre life than the poor.” I told Meera that given my unprivileged upbringing, my mission is to help young scientists from all backgrounds fulfil their passion for understanding the Universe. In fact, the art of paying it forward was practiced by the cosmos at large, which provided a fertile ground for our intelligence to blossom in it.
We should be grateful for our cosmic existence. In addition to Mother’s Day, Father’s Day and Earth Day, we should celebrate Cosmos Day every year. Below are a few reasons to extend our gratitude to the Universe.
Let us start with the vacuum before we even dwell on the benefits of matter. Dark energy represents the mass density of the vacuum which is causing the accelerated cosmic expansion at present. As the Universe expanded, matter and radiation were diluted and the vacuum eventually dominated the cosmic mass budget. In our cosmic future, the accelerated expansion will prevent the assembly of matter into bound structures. If the dark energy had a much higher density, this would have happened in our past. As a result, there would have been no galaxies like the Milky-Way inside of which stars like the Sun form, next to which planets like the Earth emerge, on which the chemistry of life-as-we-know-it in liquid water takes place.
This has all to do with the vacuum having a low mass density. But our debt of gratitude extends also to the properties of cosmic matter. Naively, one might think that only the ordinary matter that makes our bodies is responsible for our existence. Our body mass is mostly water, which combines hydrogen atoms from the Big Bang with oxygen produced by nuclear fusion of hydrogen in the cores of stars. But this point of view is naive. In fact, we owe our existence first and foremost to dark matter, a substance which constitutes 85% of the mass budget of cosmic matter and whose nature is unknown.
My recent essay about the invisible matter in the cosmos stated: “We know that dark matter exists based on its gravitational influence on ordinary matter that we detect in the form of stars and gas.” After reading this essay, the eye specialist Dr. Robert Cykiert wrote to me: “Since that’s the only significant evidence we have for dark matter, an alternative hypothesis might be that we aren’t understanding and measuring gravity correctly especially at mega-distances or when mega-masses are involved. Newton’s formula for the force of gravity was good for a few hundred years until Einstein came along.”
I replied to Robert that indeed it is possible that gravity is modified. But even in that case, there must have been some dark matter in the cosmos. The reason is that early on in cosmic history, ordinary matter was tightly coupled to radiation, currently observed as the cosmic microwave background. The radiation was smooth. Because of the coupling, ordinary matter was also smooth. However, dark matter was not coupled to any of them and so it kept memory of the initial density inhomogeneities on the scale of galaxies. This is the reason that galaxies, like the Milky Way, exist. Without dark matter, the Sun or Earth would have never been seeded, and we would not exist. We owe our existence to dark matter. Modifying gravity without any dark matter would not have accommodated our existence.
We should also count our blessings that the mass budget of ordinary matter is similar but somewhat smaller than that of dark matter. This allowed dark matter to dominate gravity, triggering the assembly of galaxies by maintaining memory of the initial density perturbations that seeded them. Fortunately, the ordinary matter was not diluted too much relative to the global mass budget so that stars could have formed out of cold gas clouds inside these galaxies.
The abundance of ordinary matter is related to a slight asymmetry between matter and antimatter in the early universe, at a level of a part in 1.6 billion. We do not understand what triggered this tiny asymmetry and why it led to the ordinary matter not being too diluted or overabundant relative to dark matter. Perhaps the fact that ordinary matter and dark matter have comparable mass budgets implies that the two are related. If the asymmetry between matter and antimatter had not existed, the universe would have had negligible amounts of ordinary matter today. Almost all of it would have annihilated into the cosmic radiation background. We would have been ghosted by the Universe as ordinary matter would have been consumed in the faint radiation glow of the Big Bang.
Finally, we must be grateful that our intelligence allows us to appreciate the grand beauty of the cosmos as the greatest work of art ever made. We share our life with less intelligent beings like microbes, but intelligence gives a meaning to our existence. To fully appreciate how fortunate we are, we must actively search for cosmic partners. They will alleviate our sense of cosmic loneliness, improve our mental health and inspire us to do better in their company. This quest is my lifelong mission, adding an extraterrestrial context to Meera’s passion of giving back to humanity.
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. His new book, titled “Interstellar”, was published in August 2023.
