Since the discovery of gigantic, ancient dinosaurs, scientists have struggled with the question: what made them go away? The prevailing theory is that they were wiped out by asteroid impact, though there are alternative theories that a string of volcanic eruptions suffocated the planet, making it uninhabitable to these giants.
But what if (and it's a big if) something else was to blame? Well, putting out an interesting but "out there" theory, one physicist has suggested that the extinction of the dinosaurs may have been brought about by something much more fundamental: A change to the values of physics itself.
It all comes down to the Hubble Constant – the expansion rate of the universe. In order to calculate the rate of expansion of the universe, we can measure the distance and velocity of nearby galaxies, quasars, and supernovae. Another way of measuring the rate of expansion is to look at the cosmic microwave background, which shows us the expansion rate in the early universe, before extrapolating to today.
Physics, of course, chooses to be a jerk about this, and the methods produce very different results. The universe expansion appears to be getting faster and faster, and barring some error we haven't yet picked up on, this discrepancy needs to be explained by new theories, such as dark energy, which have so far proved inadequate.
So far, so not dinosaury. However, Professor Leandros Perivolaropoulos of the University of Ioannina in Greece has a theory that he believes reconciles the discrepancies in the expansion rates gained from each measurement method, and, as a bonus, wipes out the dinosaurs to boot.
In a paper published on pre-print server Arxiv titled "Is the Hubble crisis connected with the extinction of dinosaurs?", Perivolaropoulos suggests that a 10 percent increase in the strength of gravity took place over 100 million years, ending 50 million years ago.
"Physical mechanisms that could induce an ultra-late gravitational transition include a first order scalar tensor theory phase transition from an early false vacuum corresponding to the measured value of the cosmological constant to a new vacuum with lower or zero vacuum energy," he writes in the paper, which has not yet been peer-reviewed.
The idea of a false vacuum is as interesting as it is potentially terrifying, being as it could – in theory – mean the universe as we know it will collapse on itself, taking everything – from olives to supernovae – with it.
Everything in the universe wants to be in a stable state, which comes from having as little energy as possible. Vacuums have the lowest level of energy, and therefore have the most stability. However, there is a hypothetical idea known as a "false vacuum". These are local vacuums that appear to be at the lowest level of energy, but are actually not so. For a time, the false vacuum – acting like a local bubble – would appear stable, but could collapse upon contact with a true vacuum, as the false vacuum falls to the lower energy state.
Picture a valley in front of you, concealing a deeper valley below a thin surface. The false vacuum is the smaller valley, but say the thin surface is pierced, it collapses into the larger valley below: the true vacuum. In the worst-case scenario, this could collapse our entire universe, but in Perivolaropoulos' theory this may have happened already to our local false-vacuum bubble, changing the strength of gravity as it did.
The change in the value of gravity, he believes, would alter the properties of supernovae (and all objects in the observable universe, in fact) explaining the discrepancies between measurements of the early universe and measurements of expansion today.
Now we get to the dinosaur-killing. The paper suggests that a 10 percent increase in gravity would disrupt the Oort cloud – a big bubble of billions or even trillions of icy objects at the outer reaches of our solar system – and send objects our way at an increased rate. Something which he believes can be observed in the geological record.
"A sudden increase of the gravitational constant by about 10 percent taking place less than 100 million years ago can justify the observed rate of impactors on the Earth and Moon surfaces which appears increased by a factor of two-three during the last 100 million years and may be connected with the Cretaceous-Tertiary (K-T) extinction event eliminating 75 percent of life on Earth (including dinosaurs)," he wrote in the paper, adding "if such a gravitational transition has indeed taken place it should have left signatures in a wide range of astrophysical and geophysical data."
He goes on to write that “the impact flux of kilometer-sized objects increased by at least a factor of two over that last 100 million years compared to the long-term average."
While the theory is no doubt interesting, and, let's face it, pretty cool as a concept, it does somewhat smack of trying to make facts fit the theory.
“In principle, a change in gravity would affect the dynamics of the Oort Cloud, leading to collisions between comets that could then put some of them on trajectories towards the inner solar system," astronomer at the University of New South Wales in Australia, Ben Montet told the Daily Beast, adding that if that were the case we would be able to see the effects of the orbit change on planets, as well as geological impacts on Earth, Mars, and Venus.
“There is no geological evidence to believe this is the case," he concluded, pointing out that the Chicxulub impact with Earth that killed the dinosaurs was an asteroid, not an icy comet as you would expect from a body sent our way from the Oort cloud, where only one in every 25 objects is expected to be an asteroid.
Perivolaropoulos himself is aware that evidence for the theory is lacking, but believes there could be ways to confirm or refute it.
"The temperature of Earth strongly depends on the value of [gravity] and so does the solar luminosity," he concludes. "Thus an increase of [gravity] would lead to a similar increase in the Earth temperature. Thus a careful search of unaccounted for temperature variations of Earth during the past 150 million years could either impose strong constraints on the gravitational transition hypothesis or could reveal possible signatures of such an event."
Through this, or through closely studying the rotation of local galaxies, he believes we could pick up hints as to whether the dinosaurs were killed by an asteroid flung our way by a fundamental change to the strength of gravity in our local universe.