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Rated 5 out of 5 by Anonymous from Excellent Course! Kudos to Dr. Lincoln for a thought provoking course. I appreciated the stimulating content and also the presentation which was witty and engaging. Another reviewer complained that Dr. Lincoln referenced other course titles that might be useful for in-depth subject pursuit. I did not consider that a bug but rather a feature!

Date published: 2025-12-02

Rated 4 out of 5 by Jack T from Question for Dr. Lincoln I have purchased all of Dr. Lincoln's great courses lecture series and find them marvelous. I seem to recollect that I can post a question for him on this site. Why in the second lecture does he come up with a minimum relative size of a curved universe by dividing by .002 rather than .0027? Also, if the uncertainty is expressed as the standard error, maybe he should divide by .0054 to be at the 95% certainty level. Finally, and this is just a comment, at one point in the first lecture he mentions the universally accepted view that the universe is very close to 13.8 billion years old. That being the case, I find it a bit offputting that he often refers to to it as 14 billion years old. I enjoy the precision that characterizes his lectures. He is precise in stating that the universe became transparent to light at 380,000 years. He did not round that to 400,000 years.

Date published: 2025-12-02

Rated 5 out of 5 by Gyrfalcon from Science at the Edge The Astronomer and broadcaster Neil deGrass Tyson once explained a curious paradox - the more we know the more questions we have. He imagined all we know as a sphere, and the frontier of knowledge as the area of surface of the sphere as the boundary between what we know, on the inside, and what we don't yet know on the outside. As we gain more knowledge, the volume of the sphere increases, but so does the area of the sphere - the interface between the known and the unknown. In other words, the more we know, the more questions we have - and the more science there is to do! In this course, chief Fermi Lab scientist and communicator, Don Lincoln leads us through some of the most interesting questions in Physics and Cosmology, right at the cutting edge of Science. He expertly explains, to both laymen and what is known, what is unknown, and how scientists of multiple disciplines are working together to bridge the gap. Highly recommended.

Date published: 2025-11-26

Rated 5 out of 5 by the professor from Physics Questions by a Powerhouse Professor! Dr. Don Lincoln is a powerhouse in the field of physics, and this course is shining example of his ability to make complex ideas accessible, engaging, and deeply thought provoking. As a senior scientist at Fermilab and a member of the large team that discovered the Higgs boson, his credentials are impeccable. Yet, what makes him truly remarkable is his gift for communication, as he combines authority with warm humor and clarity. Across 24 half hour lectures, Dr. Lincoln explores some of the most profound mysteries in physics. He leads off with a critical question, How Big is the Universe? What happened before the Big Bang and why is the universe flat? The professor flows into the cosmological principle and is it valid? One aspect of the discussion I greatly appreciate is Dr. Lincoln giving credit to the lesser known contributors of cosmological research such as this reviewers favorite Monsignor Georges LeMaitre, whose research was published in an obscure research document and not given credit until Hubble's published research. This writer highly recommends the book, The Primeval Atom by the Monsignor as support of the theory. Additionally, Dr. Lincoln recommends numerous other The Great Courses lecture sets, all of which this writer has learned so very much from, especially Dr. Sean Carroll's lectures. What sets this course apart is Dr. Lincoln's balance between what we know and what we don't know yet. He never oversells certainty: instead, he invites learners into the frontier of human understanding, showing both the beauty and the limits of current science. His friendly demeanor, humor, and ability ground abstract concepts in reality makes each lecture a pleasure to watch. Having previously enjoyed his course The Theory of Everything, I can confidently say this series is among the very best! I have enjoyed well over 1100 TGC's lecture sets since 2002, and Dr. Don Lincoln is in the top tier! This is a five star course which leaves the learner with a deeper appreciation for the mysteries of the universe and the joy of scientific inquiry. I definitely look forward to additional Dr. Don Lincoln lecture series!

Date published: 2025-11-17

Rated 5 out of 5 by TheVillageIdiot from Dr. Lincoln does it again! Such a privilege. There's a saying that goes "Whenever you have more questions than answers, you know your on the right track." Dr. Don Lincoln is great a breaking down complex concepts into bite size peices that are easily understood. Then pulls it all together for you. The title of the course is "The Great Unanswered Questions of Physics". So if you walk away knowing the answers to questions that the most brilliant minds in the world are wrestling with then you my friend need to look up the closest University and run, don't walk to their physics department, look up; a professor and plop your keaster down in his office. Don't worry, they're used to weirdos. ;

Date published: 2025-11-09

Rated 1 out of 5 by Kuro89 from Every other sentence is an ad Every other sentence is an ad for a different course you should watch instead of letting this one be selfcontained. Very little actual content. AI autosubtitles are unusable... The great courses isn't so great anymore

Date published: 2025-11-07

The Great Unanswered Questions of Physics

Trailer

01: How Big Is the Universe?

Dr. Don Lincoln, a particle physicist at Fermilab, sets the stage for your course with a foundational question: How big is everything? Because the visible universe is limited to how far light has been able to travel over the past 14 billion years, we must turn to the cosmic microwave background (CMB) to gauge the full scope of the universe.

31 min

02: What Is the Shape of the Universe?

Travel back to the earliest seconds of the universe to consider its density and temperature. Using that information, plus Einstein’s theory of general relativity, we can gain insight into the overall size and shape of the universe. Although the picture is still fuzzy, breakthroughs in measuring temperature offer possible clues.

31 min

03: Is the Cosmological Principle Valid?

The “cosmological principle” posits that the universe is homogeneous. However, recent analysis of CMB, cold spots in the universe, and the distribution of galaxies leaves open the question of whether the universe is essentially the same everywhere—or whether some spots, such as our own, might be special.

31 min

04: What Happened before the Big Bang?

The traditional model of the Big Bang was that the universe exploded out of an infinitely dense singularity, but we have no way to measure those early moments or what might have come before them. Here, review our current understanding of the Big Bang and explore speculations such as cyclical universes and multiverse collisions.

31 min

05: What Is Time?

Time feels familiar to us all, but it’s an enigma in the world of physics. In Newtonian physics, time moves forward linearly, but Einstein’s theory of special relativity adds a twist to what we call “spacetime.” Examine the concept of “time’s arrow,” with an introduction to entropy and thermodynamics.

30 min

06: Why Did the Cosmos Start with Low Entropy?

Here, your exploration of entropy (disorder in a system) leads to a mind-bending look at the history of the universe. Was the early universe high- or low-entropy? And if the early universe had higher entropy than today, how do we explain time’s arrow, since entropy usually increases over time?

32 min

07: What Is Space?

Shift your attention from time to space, which you will discover is more than a cosmic backdrop for stars and galaxies. Mathematically, space is a framework for physical equations, but physically, space is a dynamic entity that supports light, fields, and gravity. For scientists, the true nature of space remains a mystery.

31 min

08: Are There Multiple Universes?

The “multiverse” hypothesis suggests there may be multiple universes beyond our own. Physicist Max Tegmark has created a classification system for such a reality, from infinite universes to quantum splits and more. Dig into the evidence for and critiques of this fascinating speculation.

32 min

09: Why Is Gravity Weaker than Other Forces?

In an introductory physics course, the force of gravity is hugely important, yet it is the weakest among the four major forces. The strong nuclear, weak nuclear, and electromagnetic forces are much more powerful, but why? Is gravity seeping into other dimensions? Consider what might be going on at the subatomic level of reality.

31 min

10: Why Does Gravity Move at Light Speed?

Despite being the weakest of the four fundamental forces, gravity plays an outsized role at the cosmic scale, operating on planets and stars at the speed of light. How does this work? And how do we even know? Unravel this mysterious phenomenon with a little help from a neutron star collision.

32 min

11: What Does the Wave Function Mean?

Unlike the discrete world of classical mechanics, the quantum world operates on probability. The root of the quantum world is Schrödinger’s wave function, which helps us determine a particle’s location. Unpack the counterintuitive world of particle physics, in which objects are also waves.

30 min

12: Where Did All the Antimatter Go?

Matter is all around us, but evidence about the Big Bang and Einstein’s theory of special relativity both suggest the universe should be filled with antimatter. Where is this peculiar substance? Here, Dr. Lincoln takes you through the ongoing search and lays out the theories and experiments scientists hope will solve this puzzling phenomenon.

33 min

13: Is Dark Matter Real?

As with anti-matter, observed phenomenon and the math behind it predict something called “dark matter”—invisible particles interacting with gravity. From modified Newton dynamics (MOND) to bullet cluster collisions among galaxies, see where the evidence points about the hidden layer of reality.

32 min

14: Is Dark Energy Constant over Time?

You learned earlier in this course that the universe was expanding. Here, you will deepen your understanding with a look at how dark energy is accelerating the expansion. Physicists are investigating whether dark energy is constant or changing, and whether the fate of our universe will be a “Big Rip” or a “Big Crunch.”

32 min

15: Does Inflation Save the Big Bang Theory?

The Big Bang theory seems to conflict with the relatively flat shape of the universe. The concept of “inflation” (astrophysical, not economic) might explain numerous holes in the Big Bang theory, including the universe’s flatness and uniformity. Find out what all of this means and what future experiments may tell us.

32 min

16: How Do We Explain the Hubble Tension?

Continue your study of discrepancies in the field of cosmology. The “Hubble Tension” refers to a conflict of two mathematical constants in the universe’s current expansion rate, which arises from looking at distant stars and supernovae. Dr. Lincoln walks you through the cosmic distance ladder versus CMB-based predictions.

33 min

17: What Is the Smallest Building Block?

The ancient Greeks gave us the concept of atoms as tiny building blocks of matter, but it wasn’t until the 20th century that particle physics exploded onto the scene. From Murray Gell-Mann and George Zweig introducing quarks to the results of atom-smashing in the Large Hadron Collider today, find out about the deepest structure of matter.

32 min

18: What Happens inside a Black Hole?

What lies beyond the event horizon of a black hole? General relativity suggests they might be singularities of zero size and infinite density, where not even light can escape. In this lecture, you will traverse the Milky Way, survey gravity waves, reflect on time dilation, and get to know the untestable realm of astrophysics.

31 min

19: How Did the First Galaxies Form?

The formation of the first stars and galaxies is as mysterious as the Big Bang. Scientists speculate that after the early universe cooled, hydrogen and helium atoms formed, dark matter drove gravitational clumping, and primordial gases exploded as supernovae, eventually leading to the stars and galaxies we know today.

33 min

20: How Did Supermassive Black Holes Form?

Travel to the center of the galaxy to encounter a supermassive black hole. Is there a connection between these enigmatic solar masses and the formation of galaxies? Do they regulate a galaxy’s growth? Trace the evidence for why supermassive black holes form and what role they play in cosmic evolution.

30 min

21: Are the Constants of Nature Constant?

In everyday physics, we take it for granted that nature’s fundamental laws such as the speed of light are constant. But the universe after the Big Bang was a strange place and may not have operated under the model that has remained constant for the past 10 billion years. Delve into the domain of quasars and particle accelerators to explore this issue.

29 min

22: How Does Quantum Gravity Work?

One of the significant unknowns of modern physics is why Newton’s laws fail at the quantum level. Physicists are in hot pursuit of a so-called “theory of everything” to unify gravity on the cosmic scale with quantum theories. This lecture surveys two possible solutions: superstring theory and loop quantum gravity.

30 min

23: How Can We Measure Zero-Point Energy?

Cosmic and quantum physics both suggest a massive quantity of energy may exist in the empty spaces of the universe. Pseudo-scientists have suggested someone could get rich from harvesting this “zero-point energy,” but actual scientists have a different view. Separate fact from fiction in the world of energy.

31 min

24: Is the Universe Stable?

Your course wraps up with a provocative question: Could the universe vanish in an instant? From cosmic inflation to the electroweak theory to measurements of the Higgs boson particle, find out how stable our universe truly is and how the cosmic world might unravel via some improbable quantum event.

32 min

Overview Course No. 10680

What happened before the Big Bang? Why does time flow only forward? Do we live as part of a multiverse? Could the universe vanish in an instant? These questions and more are at the forefront of physics, cosmology, and quantum theory, and they keep some of the best minds of modern physicists awake at night.

The Great Unanswered Questions of Physics gives you the chance to probe these mysteries of the universe. Taught by Dr. Don Lincoln, an esteemed particle physicist and a senior researcher at Fermilab, these 24 captivating lectures delve into some of the most vexing cosmic and quantum puzzles. From the strange behavior of subatomic particles to the enigmas of supermassive black holes at the center of a galaxy, Dr. Lincoln blends engaging storytelling with rigorous science as he brings to life the cutting-edge questions of 21st-century physics.

With decades of real-world expertise, he unravels the challenging concepts of physics at both the cosmic scale—stars, galaxies, black holes, and the Big Bang—and the quantum scale—dark matter, the fundamental forces, and the search for a unified “theory of everything.” As much as the “what” of these enigmas, Dr. Lincoln delivers the “how.” You’ll learn to think like a scientist as you walk through the business of theorizing, testing, rethinking, and testing again. Many of these unanswered questions will not be answered in our lifetime, but as you will see, the joy of scientific inquiry is in the journey, not the destination.

About

Don Lincoln

There are so many clues from physics that are staring at us in the face. They are telling us something profound.

ALMA MATER

Rice University

INSTITUTION

Fermi National Accelerator Laboratory (Fermilab)

Don Lincoln is a Senior Scientist at Fermi National Accelerator Laboratory (Fermilab). He received his PhD in Experimental Particle Physics from Rice University and was involved in the discovery of the top quark and the Higgs boson. He has written several books for the public and many articles for media outlets such as CNN, NOVA, Scientific American, and Live Science. He has also produced more than 100 videos hosted on the Fermilab YouTube channel. For his science outreach, he received the Andrew Gemant Award from the American Institute of Physics.