On March 18th, astronauts Sunita Williams and Butch Wilmore returned from the International Space Station (ISS) after their unscheduled nine-month stay in orbit. There has been much concern expressed around Williams and Wilmore’s health, having survived the harsh conditions of outer space. Yet if anything, the duo came out younger than we did in the interim period – thanks to strange physics that we typically don’t encounter daily.

Williams and Wilmore lived in a weak gravitational environment throughout their stay up in space; at the least compared to everyone else on earth. At that altitude 450 km above the surface, Einstein’s theory of relativity came to play – slowing down time for the astronauts.

When clocks run slow

In Einstein’s general theory of relativity, gravity is better explained as the distortive effect in an abstract continuum called space-time. This is quite distinct from Newton’s explanation of gravity, of invisible attractive forces emanating from masses themselves. In relativity, matter and energy twist both space as well as time. Imagine a thin fabric of material. Mass and energy are akin to heavy objects producing depressions in them.

Although we don’t encounter relativistic effects in our everyday encounters in life, their effects are subtle but measurable. The difference in gravity’s strength here produced a noticeable time dilation. Stronger the gravity, the slower does time flow for that person. This means people on earth aged slightly more with respect to the astronauts. This should mean that astronauts spending time up in space should have aged faster due to gravitational time dilation alone.

Except, there is yet another source of time dilation that contributes to aging – and that is, velocity. The ISS zips through low-earth orbit at speeds clocking nearly 28,800 km/h – or 8 km/s. That’s faster than a typical intercontinental ballistic missile when it’s mid-way in its journey. Space-time can distort tangibly when an object possesses incredible energy – and not just gravity. Time dilation from the ISS hurtling at such tremendous speeds, outsized the effect from earth’s gravity. And the resultant time flow would be slower than usual.

In effect, the duo aged slower, by approximately 0.0075 seconds. Virtually, there is no difference as you might notice. But with a good atomic clock though, time dilation can be demonstrated as a subtle, yet measurable effect. In fact, engineers have exploited the effect to solve technical problems arising with global positioning system (GPS) satellites, to coordinate and ensure positional accuracy. The high-precision atomic clocks on-board GPS satellites help software correct for latency errors, accounting for time dilation as well.

In 1924, American astronomer Edwin Hubble discovered that our universe expands in all directions. Powering this expansion was a Big Bang, an event that marked the birth of our current universe some 13.7 billion years ago. Back then, the finding came as a jolt to the astronomy community and the whole world. In 1998, there was even further shake-up when observations of type 1A supernovae from distant galaxies indicated the universe was expanding – at an accelerated rate. But the source of its driving force have remained in the dark.

Dark energy was born from efforts to explain the accelerated expansion. It remains a placeholder name for an undetected energy density contribution that offers a repulsive effect counterbalancing gravity’s attractive nature at long distances. Consensus emerged in support of this dark energy model thereafter. In 2011, astronomers behind the type 1A supernovae study went on to share the Nobel Prize in Physics.

More than two decades later, we are none the wiser to uncover what dark energy is. However, cosmologists have deemed it to be a constant of nature, one that does not evolve with time. So was the surprise when preliminary findings from the Dark Energy Spectroscopic Instrument (DESI) survey indicated dark energy was not just variable, but also weakening over time. The Lambda-Cold Dark Matter, more technically known as the standard model, has never stood on shakier grounds.

Fine-tuned to a Big Crunch ending

In cosmological models, the Greek letter “Lambda” fits as a placeholder for dark energy. It depicts a major chunk – some 70% of the universe’s energy density. But this figure holds only if it is a true cosmological constant. If dark energy is variable, then inevitable we end up fine-tuning the universe’s fate. A constant dark energy would yield a universe expanding forever.

But going by DESI’s preliminary findings, if dark energy is weakening over time, the the universe is set to collapse on itself in the far future. This is the Big Crunch hypothesis. It was amidst the caucus surrounding DESI’s latest findings, the cosmology community took interest in a paper published in the December edition of the Monthly Notices of the Royal Astronomical Society.

In 2007, David Wiltshire, a cosmologist at New Zealand’s University of Canterbury, and the paper’s co-author, had proposed an alternate model called timescape cosmology, to get rid of dark energy entirely. It requires a sacrifice over an assumption cosmologists have held so sacred in their models. Known as cosmological principle, it shares much in common with Aristotle and Ptolemy’s outdated viewpoint that the earth was at the center of the solar system.

A special place in the universe

The cosmological principle assumes matter in the universe is distributed uniformly everywhere on average, and in every direction that we look around. But cosmologists propose to adopt a pragmatic approach like the Polish Prussian astronomer, Nicholas Copernicus, had proposed in the 16th century. In the Copernican model of the solar system, the earth bore no special location in it. Likewise, timescape cosmology requires earth to not occupy a special location.

Saying that, the cosmological principle has a certain appeal among cosmologists. Theoretical calculations would appear complex to manipulate discarding uniformity. At the same time, cosmologists do contend that something has to give way, in light of astronomical observations that contend the cosmological principle is indeed outright wrong.

Inhabiting a time bubble

One of the hallmark phenomena in Einstein’s general theory of relativity is gravitational time dilation. Time passes slower under a gravitational field. Bizarre as though it may seem to be, experiments have proven this subtle, but measurable effect.

In 1959, two Harvard physicists Robert Pound and Glen Rebka Jr. used a pair of atomic clocks to demonstrate this effect – also known as gravitational time dilation. Two clocks were stationed in their office building – one atop the roof, and the other closer to earth. The clock stationed closer to earth, lagged in comparison to the one atop the roof. Here, time dilation occurs in response to earth’s gravity tugging weakly at the clock atop, compared to the one below.

The universe looks clumpier in certain directions at cosmic scales than others. Galaxies bind together under gravity to form strands like that of a vast, interconnected cosmic web. Voids of cosmic proportions occupy the space in between. These voids experience a faster time flow, since they’re subject to weaker gravity from the surrounding galaxies. But observers in these galaxies have a skewed perception of time, since they’re living embedded inside a bubble of strong gravity. Events outside their time bubble play out akin to a fast-forwarded YouTube video.

Not the end of dark energy

Distant galaxies appears to recede accelerated in the reference frame of our time bubble. That appearance is a mere temporal illusion; an effect David Wiltshire says we falsely assume to be dark energy. So far, timescape cosmology has only occupied a niche interest in cosmology circles. There is far too little evidence to support a claim that dark energy affects arise truly from us inhabiting a time bubble.

Cosmologists had taken to social media to critique Wiltshire’s use of type 1A supernovae datasets used in his analysis. Saying that, none of the critiques themselves are conclusive. As observations pile up in the future, there may come a definitive closure. Until then it’s a waiting game for more data and refined analysis. Meanwhile on the contrary, it is too early to abdicate dark energy as a concept altogether. Lambda-CDM model would be the first to undergo a major rehaul, should DESI’s preliminary findings hold in successive observational runs. Until then, we can only speculate the universe’s fate.

The ability to control the behaviour of individual cells has long been a goal of scientists studying cell development. MIT researchers have now developed a method to manipulate how a single cell moves and changes shape, using light. This breakthrough, which could have far-reaching applications in synthetic biology and medicine, was demonstrated in egg cells from starfish—a common model for understanding cell behaviour during development.

The team, led by Nikta Fakhri, focused on an enzyme within the starfish egg cell that triggers a cascade of movements. By genetically engineering a light-sensitive version of this enzyme, the researchers were able to use light to direct the cell’s motion in precise patterns.

“We found that the light successfully triggered the enzyme, which in turn prompted the cells to jiggle and move in predictable patterns,” says Fakhri, an associate professor of physics at MIT. “For instance, we could stimulate cells to exhibit small pinches or sweeping contractions, depending on the pattern of light we induced. We could even shine light at specific points around a cell to stretch its shape from a circle to a square.”

The findings, set to be published in Nature Physics, open up exciting possibilities for future medical and synthetic cell applications. The researchers envision using this technology to design cells that could respond to light for therapeutic purposes, such as “patch” cells that contract to help close wounds or drug-delivering cells that release medication only when illuminated at specific locations in the body.

Fakhri continues, “By revealing how a light-activated switch can reshape cells in real time, we’re uncovering basic design principles for how living systems self-organize and evolve shape.”

The research team includes MIT’s Jinghui Liu, Yu-Chen Chao, and Tzer Han Tan, alongside collaborators from Ludwig Maximilian University of Munich, Saarland University, and the Whitehead Institute for Biomedical Research.

Exploring the Starfish Model

Fakhri’s group specializes in understanding the physical dynamics that drive cell growth, especially the role of symmetry in cell development. The starfish, known for its distinct stages of symmetry, is an ideal organism for studying the signalling processes that guide cell organization.

“A starfish is fascinating because it starts with a symmetrical cell and eventually develops into an adult with pentameral symmetry,” Fakhri explains. “There are many signalling events along the way that direct how the cell organizes itself into more complex structures.”

The team’s earlier research identified a key “circuitry” in the starfish egg cell that regulates its movement and shape. This circuitry involves an enzyme called GEF, which, when activated, triggers a protein called Rho. Rho plays a crucial role in regulating cell mechanics by binding to the cell’s membrane and initiating the formation of muscle-like fibres that enable the cell to contract and move.

Harnessing Light to Control Cell Movement

In this new study, the team turned to optogenetics, a technique that uses light to control genetically engineered cellular components. They created a light-sensitive version of the GEF enzyme and injected it into egg cells harvested from starfish. The cells, now capable of producing the light-sensitive enzyme, were placed under a microscope, and the researchers applied light in different patterns to observe how the cells responded.

By targeting specific areas of the cell with light, they were able to activate the enzyme, triggering the Rho protein to form fibers and cause the cell to move. This allowed the team to control the cell’s shape, even morphing it from a circle into a square. Additionally, they discovered that shining light in a single spot could initiate sweeping contractions within the cell, providing even more precise control over its behaviour.

“We realized this Rho-GEF circuitry is an excitable system, where a small, well-timed stimulus can trigger a large, all-or-nothing response,” Fakhri says. “By illuminating either the entire cell or just a small region, we can control how the cell responds and causes contraction or pinching.”

The researchers also developed a theoretical framework to predict how cells would change in response to light stimuli. This new understanding of cellular “excitability” could have important implications for fields like developmental biology, wound healing, and synthetic biology.

Future Applications in Synthetic Biology

“This work provides a blueprint for designing programmable synthetic cells,” Fakhri explains. “By controlling cell shape in real time, we can potentially design cells that perform specific tasks in the body when activated by light. This could lead to new biomedical applications, from targeted drug delivery to tissue repair.”

The ability to control cell behaviour with light opens up exciting possibilities for future research and applications, offering a new way to explore how cells shape themselves during development and how we might harness these processes for therapeutic use.