Category: SCIENCE

Einstein’s General Relativity has reigned supreme as our theory of gravity for over a century. Could we reduce it back down to Newton’s law?

Although Einstein is a legendary figure in science for a large number of reasons — E = mc², the photoelectric effect, and the notion that the speed of light is a constant for everyone — his most enduring discovery is also the least understood: his theory of gravitation, General Relativity. Before Einstein, we thought of gravitation in Newtonian terms: that everything in the universe that has a mass instantaneously attracts every other mass, dependent on the value of their masses, the gravitational constant, and the square of the distance between them. But Einstein’s conception was entirely different, based on the idea that space and time were unified into a fabric, spacetime, and that the curvature of spacetime told not only matter but also energy how to move within it.

Despite these conceptual differences, in nearly all practical cases, Einstein’s equations and Newton’s law of universal gravitation yield identical predictions. Does that imply that Einstein’s equations can somehow be collapsed, or reduced, down to Newton’s laws? It’s what James Raymond wants to know, asking:

“It seems like an amazing coincidence that Einstein’s equations give almost exactly the same result as Newton’s law of gravity. Popular lectures on gravity never seem to address this. I suspect it is not a coincidence. Is it possible to make a tiny change in Einstein’s equations to make them collapse to Newton’s law?”

It’s a great question, and one with a very nuanced answer. Yet, we can modify Einstein’s equations to recover Newton’s law. But no, it’s not a “tiny” change; it requires ignoring the most Einsteinian aspect of the theory of all: the principle of relativity itself. Here’s what it all means.

Newton’s law of universal gravitation is perhaps the best place to start: because it’s so apparently simple and straightforward. It simply says, as…

Our scientific instruments are constantly improving, revealing nature’s workings as never before. Without them, we’ll remain in the dark.

Whenever we perform science at the frontiers — probing the Universe, at some level, in ways, with instruments, or at precisions that we’ve never achieved in all our prior interrogations of it — there’s an incredible puzzle that arises. On the one hand, we design and build our tools and experiments to be sensitive to things that we strongly suspect ought to be out there, but that we haven’t yet been able to confirm or refute with concrete evidence. When we built the James Webb Space Telescope (JWST), for example, we knew we were going to break many records: for most distant galaxy, for the youngest supermassive black hole, for the earliest galaxy cluster to form in the Universe, and much more.

After all, we designed it with capabilities that would render it uniquely equipped to surpass the limits of all prior observatories: from the space-based Hubble, Spitzer, and WISE telescopes to the ground-based Very Large Telescope, Keck, Subaru, Gemini, and Magellan Telescopes, and even the current world’s largest optical telescope: the Gran Telescopio Canarias. And yet, on the other hand, those very capabilities enable it to make the biggest discoveries of all: discoveries that we couldn’t have even foreseen would be there to make, as nature’s imagination frequently surpasses our own.

Here, using JWST as an example, we can see the importance of investigating the Universe in ways that fundamentally take us beyond all previous limitations. The lessons we frequently learn simply by looking humble us into realizing how ignorant we were, previously, of what we didn’t even realize we didn’t know.

Back when JWST was first being conceived, the idea was relatively simple and straightforward. We had designed, built, flown, and conducted science with space telescopes previously, and for a long time at that. After all, going to space gives you a huge advantage over astronomy conducted on the ground: you no longer have Earth’s atmosphere to contend…

When we see spiral galaxies, some are face-on, others are edge-on, but most are tipped at an angle. But which side is closest to us?

All throughout the Universe, spiral galaxies are extremely common.

Along with elliptical galaxies, most of the Universe’s stars reside inside them.

Most observed spirals appear neither edge-on nor face-on, but tipped: inclined at an angle.

Remarkably, just by a visual inspection, you can conclude — with confidence — which edge of the galaxy is closest.

Unlocking the answer requires putting just two pieces of key information together.

The Universe is expanding, and individual, bound structures are all receding away from one another. How, then, are galaxies still colliding?

Here in our Universe, an astrophysical phenomenon continues to occur that seems paradoxical. The Universe is expanding, and the expansion itself is accelerating due to dark energy, causing distant objects to recede from one another at ever-increasing rates. When we look at galaxies, we see this directly: the farther away they are from us, the faster they recede from our perspective. Moreover, because of dark energy, if we watch any individual galaxy recede from us over time, we’ll find that it speeds up in its recession: exactly what we mean when we say that the Universe’s expansion is accelerating.

And yet, all across the Universe, both nearby and far away, galaxies — the very objects that should all be receding mutually away from one another — are seen interacting: merging, colliding, and cannibalizing one another. How are these two seemingly contradictory things both consistently true? How can the Universe be expanding, with galaxies receding away from one another, while galaxies are also finding each other, colliding and merging, simultaneously? That’s what Tom Peacock…

Since the dawn of history, humans have pondered our ultimate cosmic origins. Now in the 21st century, science has gone beyond the Big Bang.

Have you ever thought about the Universe, and asked perhaps the most profound question of all: where did all of this come from? For as long as humans have been around, we’ve not only asked these questions, but have provided stories — based on logic, reasoning, mythology, religion, and many other avenues — that allege to give an answer. Although these stories remain popular and part of human culture even today, they don’t provide any satisfactory solutions by the one criteria that matters most: can they explain what actually exists within the Universe in a scientific, reproducible way that yields accurate predictions about what we observe?

We didn’t have enough knowledge to apply that scientific approach to the entirety of the Universe until the early 20th century, and as a result, we had only assumptions to rely on about our cosmic origins. Many assumed, as Einstein did, that the Universe was static, unchanging, and eternal on the grandest of cosmic scales. But physics and astrophysics would soon point to a different conclusion: that the Universe had a birthday, and the moment of its birth…

There are some 26 fundamental constants in nature, and their values enable our Universe to exist as it does. But where do they come from?

Here in our Universe, there are three major properties that have led to it unfolding as it has:

• the laws of physics that govern all of nature,
• the initial conditions that our Universe began with,
• and the values of the fundamental constants that apply to the particles, fields, and forces in our Universe.

Over time, this has led to our modern cosmos: full of atoms, stars, planets, galaxies, galaxy clusters, and a grand cosmic web. On some of those planets, life has arisen, with at least one instance of intelligent, technologically advanced life arising on a planet known very well to us: Earth.

But what if things were just a little different? Perhaps, even with the same laws of nature and very similar initial conditions, a version of our own Universe that possessed different fundamental constants could have turned out vastly differently than our own. So why does our Universe have fundamental constants with the values that they do? That’s what Pierre Louw wants to know, following up on…

One of the most promising dark matter candidates are light particles, like axions. With JWST, we can rule out many of those options already.

All throughout the Universe, there’s a massive puzzle whose solution remains unknown: the dark matter mystery. Within every large, high-mass system that we examine, including:

• spiral galaxies,
• elliptical galaxies,
• groups of galaxies,
• clusters of galaxies,
• cosmic filaments,
• and the large-scale cosmic web,

there simply isn’t enough normal matter to explain the gravitational signals we observe. From the internal motions of galaxies to the relative motions of galaxies within a cluster to the gravitational lensing signals generated by these objects to the clustering patterns of galaxies on the largest of cosmic scales, some novel type of mass that neither absorbs nor emits light — dark matter — must be present to consistently explain what we observe.

And yet, all of our efforts to directly detect dark matter have come up empty, with key signals from particle colliders, cosmic ray experiments, and possible signatures of…

Perhaps the most well-known equation in all of physics is Einstein’s E = mc². Does mass or energy increase, then, near the speed of light?

One of the most puzzling features of nature is this: as you approach the speed of light, everything you commonly understand about motion changes. If you’re on a train moving forward at 30 m/s (about 67 mph) and you throw a baseball forward at 30 m/s from it, to someone on the ground, they’ll see the baseball move forward at 60 m/s: much faster than any human could throw it from the ground. But if that train were moving at 60% the speed of light and the baseball were thrown at 60% the speed of light, that same observer on the ground wouldn’t see that baseball moving at 120% the speed of light, but rather only at 88% the speed of light. The familiar rules of how velocities add-or-subtract is different, and more complicated, at speeds close to the speed of light.

Other, familiar rules change as well: distances appear contracted, times appear dilated, and the energy of a fast-moving particle is greater than a slow-moving particle or one at rest, too. But, particularly when it comes to energy, how can we make sense of that? Does the particle’s mass change as well? That’s what Jerry…

We’ve wasted our time and resources ideologically policing and punishing each other for far too long. Here’s a better route to prosperity.

In every civilized society around the world, there’s a trade-off that must be made. The protection of individual freedoms, on one hand, enable the people living there to pursue their own goals, dreams, and ideals, whatever they may be. But those pursuits must not infringe on the rights — including the health, safety, and general welfare — of others. When it comes to issues like the health, safety, and long-term prosperity of our society, there is no greater tool or resource we have to assess accurately them than science.

It might seem like, at the start of 2025, we’re headed in absolutely the wrong direction. Mass firings and layoffs at the NIH, the NSF, the CDC and more, coupled with the installation of a number of prominent anti-science cabinet members, the first deadly measles outbreak among children in a decade, and the USA’s withdrawal (again) from the Paris Climate Agreement all signal a national move away from science.

But this is not new. The fact is that Americans have been resistant to heeding the scientific consensus on matters of public policy for…

The full extent of the Andromeda galaxy, the nearest large galaxy to our own, has been entirely imaged with Hubble’s exquisite cameras.

Here in the Milky Way, our own galaxy’s structure remains obscure.

From within our home galaxy, even multiwavelength observations are limited.

External galaxies, however, teach us many relevant lessons.

The largest galaxy on the sky is Andromeda: 2.5 million light-years away.

Edwin Hubble observed individual stars within it in 1923, proving Andromeda’s…