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The 42 Biggest Questions About Life, the Universe, and Everything

In a homage to 'Hitchhiker’s Guide to the Galaxy,' two physicists explain the biggest unknowns in science. I’ve summed them up as a tweetstorm.
Image: Shutterstock

In Hitchhiker’s Guide to the Galaxy, Douglas Adams’ classic irreverent tour through the universe, a supercomputer named Deep Thought discovers the answer to “Ultimate Question of Life, the Universe, and Everything” after thinking about the question for 7 million years. The answer, it turns out, is “42,” but Adams never reveals what the “ultimate question” is in the first place.

In a recent paper published to arXiv, the physicists Roland Allen and Suzy Lidstrom, of Texas A&M and Uppsala University, respectively, tackled the question about the Question by describing what they believe to be the 42 ultimate questions of life, the universe, and everything.


Regarding Deep Thought’s mysterious answer, Allen and Lidstrom write that they “take it to mean that there are 42 fundamental questions which must be answered on the road to full enlightenment.” The resulting article is over 50 pages long, but is a great introduction to some of science’s biggest questions—at least according to these two physicists.

Even though its a subjective list, the paper is well worth reading in its entirety. For the sake of time, however, I’ve outlined Allen and Lidstrom’s 42 questions below as a ‘tweet storm,’ limiting the explanations to 280 characters or less.

1. Why Does Conventional Physics Predict a Cosmological Constant That is Vastly Too Large?

The cosmological constant was first theorized by Einstein and describes the energy density of the universe. The problem is that astronomical observations suggest the cosmological constant is far smaller than is predicted by physics.

2. What Is Dark Energy?

In 1998, cosmologists were astounded to find the expansion of the universe was accelerating. This astounding observation was chalked up to “dark energy,” a mysterious force that appears to make up over two thirds of the universe, but has yet to be convincingly explained.

3. How Can Einstein Gravity Be Reconciled with Quantum Mechanics?

Einstein realized that gravity, like everything else in nature, should be able to be described in terms of quantum mechanics. Yet attempts to reconcile QM and gravity fall apart when there is extremely strong gravity, like around black holes.

4. What is the Origin of the Entropy and Temperature of Black Holes?

Despite Stephen Hawking’s groundbreaking work on black hole radiation, Allen and Lidstrom note a “fundamental mystery is why the entropy should be proportional to the area rather than the volume, as is the case for other physical systems” when it comes to black holes.

5. Is Information Lost in a Black Hole?

Info is thought to be coded on the surface of its event horizon and emitted back as radiation. Yet all black holes of a particular mass radiate exactly the same, regardless of the info on the event horizon. This suggests black holes destroy info, which violates thermodynamics.

6. Did the Universe Pass Through a Period of Inflation?

It’s thought the universe expanded exponentially in the first second of its existence. The two big questions are: What is the origin of inflation and is there direct evidence of inflation?

7. Why Does Matter Still Exist?

Based on the Standard Model of particle physics, matter and antimatter should have been completely annihilated in the early universe, leaving only photons left over. Instead, there’s a relative abundance of matter and a lack of antimatter. What gives?

8. What is Dark Matter?

Observations of galaxies suggest that about a quarter of the universe is made up of dark matter, but so far physicists haven’t been able to detect a particle that can account for the observed effects. Will it be an axion, a WIMP, or something else entirely?

9. Why Are the Particles of Ordinary Matter Copied Twice at Higher Energies?

In the Standard Model, there are four main elementary matter particles—the up quark, down quark, electron, and electron neutrino. Yet there are second and third ‘generations’ (read: copies) of each of these particles such as charm quarks, strange quarks, & muons. Why tho?

10. What Is the Origin of Particle Masses, and What Kinds of Masses Do Neutrinos Have?

Where do the 4 aforementioned elementary particles get their masses? It is thought the masses are related to the strength of their interaction with their associated fields (e.g., Higgs field), but anomalies make this simple explanation in adequate.

Al-Pd-Re, a lab made quasicrystal. Image: via


11. Does Supersymmetry Exist, and Why Are the Energies of Observed Particles So Small Compared to the Most Fundamental (Planck) Energy Scale?

The Standard Model can’t explain why the weak nuclear force is so much stronger ( 10,000,000,000,000,000,000,000,000 times) than gravity.

12. What Is the Fundamental Grand Unified Theory of Forces?

The 3 non gravitational forces—strong, weak, electromagnetic—combine as elements of a single force in grand unified theory. The way these forces combine is still a mystery.

13. Are Einstein Relativity and Standard Field Theory Always Valid?

Symmetries are properties of a system that remain unchanged when that system undergoes a transformation. Charge conjuction, parity, and time reversal (CPT) is a symmetry that has never been violated, even though each element has on its own. Is CPT violation possible?

14. Is Our Universe Stable?

Aspects of the Higgs boson suggest that our universe is only “marginally stable,” or is perhaps in a transition phase to a more stable state that would result in a universe with fundamentally different properties. The question is whether our universe is stable or not now.

15. Are Quarks Always Confined Inside the Particles That They Compose?

Quarks are generally presumed to be confined within the volume of their proton and require relatively large amounts of energy to remove from this space. There is mounting evidence that quarks must always be confined, but this hasn’t been rigorously proven.

16. What Are the Complete Phase Diagrams for Systems With Non-Trivial Forces, Such as the Strong Nuclear Force?

Honestly I have no idea, so here’s a screenshot of the paper:


17. What New Particles Remain To Be Discovered?

Particle accelerators like the LHC have led to the discovery of new particles. Will it keep happening? It’s a serious question for the physicists at places like CERN.

18. What New Astrophysical Objects Are Awaiting Discovery?

Perhaps there are new kinds of stars waiting to be discovered, such as massive Population 3 stars formed during the early universe and consisting of only hydrogen and helium, or “dark stars” powered by dark matter annihilation rather than fusion.

19. What New Forms of Superconductivity and Superfluidity Remain To Be Discovered?

In the last few decades, physicists have created a number of superfluids (a fluid with no viscosity) and superconductors (materials with no electrical resistance) by exposing materials to extreme temperatures. What other materials may demonstrate these properties in the future?

20. What New Topological Phases Remain To Be Discovered?

Topological insulators are materials that act like an insulator on the inside, but are conductive on the outside. Where else will they be found?

21. What Further Properties Remain to Be Discovered in Highly Correlated Electronic Materials?

Previously mentioned topological insulators have been demonstrated in single-electron or quasiparticle systems. What other types of materials might be able to take advantage of quasiparticles?

22. What Other New Phases and Forms of Matter Remain To Be Discovered?

Researchers have found an abundance of new phases of matter in recent years such as quasicrystals and time crystals. Are there more out there waiting to be found?

23. What is the Future of Quantum Computing, Quantum Information and Other Applications of Entanglement?

The race to develop a large-scale quantum computer that could outperform a classical computer on a number of tasks, like breaking most forms of cryptography, is in full swing. But will these applications ever make it out of the lab, or are they too fragile to be anything more than a curiosity?

24. What is the Future of Quantum Optics and Photonics?

A quantum internet would help protect data from eavesdroppers, but making it happen will require unprecedented control of photons over large distances. The current record for transmitting entangled photons was set last year by a Chinese satellite. What other innovations lie ahead?

25. Are There Higher Dimensions?

If there are other dimensions, how is the ‘internal space’ of that dimension structured?

26. Is There a Multiverse?

Are there an infinite number of universes, each with its own laws? Does it just so happen that our universe is perfectly tuned for the emergence of intelligent life, an idea known as the anthropic principle? Even more important, how would we prove any of this using science?

27. Are There Exotic Features In the Geometry of Spacetime?

What is the ‘shape’ of the universe? If the universe is structured in such a way that naked singularities, wormholes, and/or closed time loops are possible, this could allow for things like traveling backwards in time.

28. How Did the Universe Originate, and What Is Its Fate?

Why is there an origin of the universe at all, and did it actually start with a bang? Looking to the past will hopefully help us understand our future and whether we’re actually heading toward a ‘big rip’ in which all matter is eventually ripped to shreds.


29. What is the Origin of Spacetime, Why is Spacetime Four-Dimensional, and Why is Time Different from Space?

I’m not sure what to add to this that isn’t already included in the header, other than you might want to get a bong before trying to tackle these questions.

30. What Explains Relativity and Einstein Gravity?

Unified theories like supersymmetry and string theory tend to assume general relativity rather than explain it. But can Einstein’s theory of gravity be derived from vacuum energy or the fields of string theory? If not, where did gravity come from?

31. Why Do All Forces Have the Form of Gauge Theories?

All forces in the Standard Model—weak, strong, electromagnetic and gravity—are described by gauge theory, which describes how elementary particles couple with specific fields. Yet why do only these kinds of forces exist and why does matter only couple to these fields weakly?

32. Why Is Nature Described by Quantum Fields?

Can quantum mechanics be accounted for by appealing to some deeper principle of the universe? This theory would explain why the universe consists of quantum fields and account for puzzling observations like the collapse of the wavefunction during a measurement.

33. Is Physics Mathematically Consistent?

Good theories are mathematically consistent with experiments. Yet relatively simple quantum field theories haven’t been demonstrated to be mathematically consistent yet.

34. What Is the Connection Between the Formalism of Physics and the Reality of Human Experience?

If mathematics and the physics it describes are effectively human creations, then we must account for the relationship between human consciousness and reality, as well as related questions like why there is something rather than nothing.

35. What Are the Ultimate Limits to Theoretical, Computational, Experimental, and Observational Techniques?

How will better computers improve our models or help us make sense of some of our most complex experiments, like the Large Hadron Collider? As our telescopes become more sophisticated, what will they reveal about the nature of the universe?

36. What Are the Ultimate Limits of Chemistry, Applied Physics, and Technology?

We live in a time of unprecedented scientific and technological advancement. Is there an upper limit to this advance, or will the rate of discovery only continue to accelerate? The question is particularly relevant to AI, which seeks to create a truly superintelligent machine.

37. What is Life?

The question was famously posed by Erwin Schrodinger in 1944. Over 70 years later, biologists are still seeking to answer this deceptively simple question.

38. How Did Life on Earth Begin?

Did organic molecules arise from a primordial soup on the early Earth, or were they transported from outer space by asteroids (a theory known as panspermia)? Moreover, how did our single-celled ancestors eventually develop into complex lifeforms?

39. How Abundant is Life in the Universe?

Robots on Mars hunt for organic matter in our own solar system and SETI astronomers are scanning the cosmic airwaves, but so far there’s no evidence of life—intelligent or otherwise—elsewhere in the galaxy. Could we really be alone in the vast expanse of the universe?

40. How Does Life Solve Problems of Seemingly Impossible Complexity?

Seemingly ‘stupid’ biologic organisms are able to perform tasks in aggregate that are staggeringly complex, such as protein folding or the ability of cells to multiply and form complex structures like eyes, hearts, brains, and other organs. Sup with that?

41. Can We Understand and Cure the Diseases That Afflict Life?

The staggering variety of biological life, even within the same species, has made curing the worst diseases incredibly difficult. Will it ever be possible to eradicate disease and death completely?

42. What is Consciousness?

It’s an issue that’s preoccupied philosophers for centuries, but only recently have we developed the technology to address this question scientifically. Is consciousness something that emerges through the complex interactions of billions of cells? Is it a spectrum? Can it be replicated?