In a massive study, a team of researchers from around the world has found a depressing, but unsurprising, result: the Universe is dying. Pretty quickly, too. This isn’t really an unexpected finding, but it’s the most detailed examination of its eventual death yet.

The study was part of the Galaxy And Mass Assembly (GAMA) Project, the largest multi-wavelength survey ever put together. The team, which was composed of researchers from across the globe, made use of some of the most powerful telescopes on the planet, including ESO’s VISTA and VST telescopes (both part of the Paranal University in Chile), as well as data from the Sloan Digital Sky Survey and NASA’s space telescopes, WISE and GALEX, and one from the European Space Agency, Herschel.

“We used as many space and ground-based telescopes as we could get our hands on to measure the energy output of over 200,000 galaxies across as broad a wavelength range as possible,” said Simon Driver (ICRAR, The University of Western Australia), who leads the large GAMA team.

That wavelength range is wide indeed, as the individual capabilities of the telescopes comprising the project stretch it from the far-ultraviolet to the far-infrared. It reveals much that can’t be seen with, say, optical-light telescopes alone. That’s because different wavelengths of light have different penetrative abilities: some can get through certain materials better than others. Also, some sources shine in one wavelength but could be too dim to be seen in another.

A brief history of our doom

The roughly 200,000 galaxies observed in the study (which can be seen in the form of a 3D map in this video, also available with music) are from three different eras of the Universe’s history, the oldest going back as far as 2.4 billion years. Back then, the Universe’s galaxies were, on average, generating more energy than they are now and releasing it in the form of light. It turns out that galaxies are currently generating about half as much as they used to be. The difference is there and it’s growing.

That doesn’t mean the Universe will have less total energy; in fact, the total energy stays the same. But a lot of that energy is in the form of mass, like hydrogen and helium, which can release some of its energy in the form of light, due to the nuclear reactions that take place inside a star.

“The Universe isn't ‘running out’ of energy, merely releasing it more slowly,” Andrew Hopkins of the Australian Astronomical Observatory, one of the paper’s co-authors, told Ars. “The energy that appeared with the Big Bang is stored in matter (hydrogen, mostly), and star formation changes the form of (some of) that energy to electromagnetic radiation, which we measure. The GAMA study makes a very precise measurement of this declining rate of emission at several epochs over the past two billion years.”

The reason for the decrease in energy production is because there are fewer stars being formed, preventing the mass locked up in that energy from being released as light.

Lost light

The light released by those galaxies is mostly being lost into intergalactic space, slowly taking the galaxy’s energy with it. The presence of dust in a galaxy can mitigate this process somewhat, absorbing some of that light and later re-emitting it.

This is similar to the function a blanket performs for your body: some of the infrared light (heat) you release is absorbed or reflected by the blanket, sending a portion of it back toward you. That heat will eventually be lost anyway, but the blanket slows the process down, keeping that heat within the person-blanket system. As such, it’ll take longer for it to cool down.

“While most of the energy sloshing around in the Universe arose in the aftermath of the Big Bang, additional energy is constantly being generated by stars as they fuse elements like hydrogen and helium together,” said Driver. “This new energy is either absorbed by dust as it travels through the host galaxy, or escapes into intergalactic space and travels until it hits something, such as another star, a planet, or, very occasionally, a telescope mirror.”

But that’s very rare, and when that light is lost from the galaxy, for the most part, it’s lost forever. Space is very big, and the light produced can go for a very, very long time without hitting something. And since the Universe is expanding, that space is getting bigger even as the light travels.

Since the Universe is producing less energy per megaparsec than it used to, and since a lot of that is being lost to intergalactic space (depending on how much dust the galaxy has), the Universe is quickly cooling off. "The Universe will decline from here on in, sliding gently into old age,” concludes Driver. “The Universe has basically sat down on the sofa, pulled up a blanket, and is about to nod off for an eternal doze.”

Doubts and details

It’s been known for some time that the Universe is headed for an inevitable icy death, but this is the most detailed measurement of the process yet performed. "The results are consistent with previous estimates that had measured the decline in the rate at which galaxies form stars," Hopkins told Ars, "but the GAMA measurements are the first to show this decline uniformly across the electromagnetic spectrum from the far ultraviolet to the far infrared."

Despite the study’s impressive precision, however, the authors make a number of important caveats. Within the vast array of data included in the study, there are some areas with uncertainties that could muddy their conclusions to some degree. As such, they point out that the work, impressive as it may be, is preliminary. Further work should be able to nail down the process even more precisely.

But the research’s main conclusions are certain, even if some of the details aren’t. “The results in the paper are remarkably robust,” Hopkins told Ars. “The caveats mentioned are related to some minor calibration issues with some of the measurements, but which are nonetheless well-constrained (simply with slightly larger uncertainties at some wavelengths than at others). The overall result does not change, although the details may change minimally—the factor of two decline over the past two billion years is not sensitive to these details.”

The researchers hope to expand their map of the Universe’s cooling further back in time, ultimately understanding how the energy production and escape has changed over the entire 13.8 billion-year history of the Universe (a much deeper history than the 2.4 billion years the team has measured so far). This will be achieved when the next wave of advanced telescopes arrives and joins the project, including the Square Kilometer Array, which will be the world’s largest radio telescope.

But while there’s more work to be done and details to be worked out, there’s no doubt of one thing: the Universe is doomed.

The arXiv. Abstract number: 1508.02076 (About the arXiv).