Ripples from another dimension

Have scientists lost their nerve in the face of a truly mind-boggling discovery? The European Space Agency (ESA) has just unveiled the cosmic findings of Planck, its orbiting observatory that has been peering into deep space for nearly four years.

And what it has found may prove to be one of the most dramatic discoveries of all time: evidence for the existence of a universe beyond our own.

The evidence takes the form of that small, circled blue spot in the image on the right. In reality, that spot is the largest object ever seen, as the image is a "heat map" of the entire universe, pieced together by Planck.

The heat comes from the radiation released during the Big Bang in which the universe was formed, almost 14 billion years ago, and the map shows the subtle differences in temperature still detectable about 380,000 years later.

Think of the image, then, as the cosmic equivalent of a snapshot of a human taken about eight hours after birth. And think of that blue spot as a "bruise" caused by a collision with a sibling universe.

That is the astounding possibility some theorists want us to consider. Not that you would have picked up much hint of this from the official announcements of the results. These focused on how Planck's findings have broadly confirmed long-standing theories about how our universe began.

Named after Max Planck, the German theorist who pioneered quantum theory, the observatory has discovered this using instruments that detect not light but microwaves, the relatively long-wavelength form of radiation into which the heat from the Big Bang has been stretched by the expansion of the universe over the past 14 billion years.

The significance of the colours in the heat map lies in the fact that the bluer, colder, regions show where the original heat has lost energy trying to escape the gravitational clutches of matter around it.

As such, the patchwork of colours reveals the spread of matter across the universe shortly after the Big Bang.

According to current theories, the Big Bang was the result of unstable force fields that filled the early universe, forcing it to undergo incredibly rapid expansion known as "inflation".

These force fields then collapsed, dumping their energy into empty space, some of which turned into matter via Einstein's famous equation linking mass and energy, E = Mc2. The charged particles of matter then came together to form atoms and molecules, which then coalesced under their own gravity to form stars, galaxies and ultimately us.

Formulated in the late 1970s, the theory of cosmic inflation predicts that the heat left over from the Big Bang should now be evenly spread out, with just a random scattering of hot and cold spots reflecting primordial subatomic "lumpiness". And this is pretty much what Planck found - at least, according to the press conferences announcing the results.

Yet one glance at the image above shows this is not the whole story. The white line cutting across the lower part divides the universe into two hemispheres, in the celestial equivalent of an equator. Clearly there is a huge region of relatively cold space to the "north" of this line, and an equally obvious band of relatively warm space below it.

Admittedly, the difference is not huge, and amounts to tiny fractions of a degree Celsius; it reveals itself only in specially enhanced images produced by the ESA.

Even so, it is unlikely to be a quirk of the data, having been glimpsed before by probes similar to Planck over the past 20 years. The origins of what some cosmologists have called the "Axis of Evil" remains mysterious, hinting of some non-random distribution of matter in the very early universe.

Potentially much more significant, however, is that cold spot, circled in Planck's map of the southern part of the night sky. Again, it had been glimpsed before, but in nothing like the detail now available.

As with the Axis of Evil, the ESA concedes it is no longer possible to dismiss it as some kind of data glitch or trick of the cosmic light. Instead, it must be taken seriously - although the space agency declined to suggest any possible explanations.

That may be because some are so outlandish that they would probably hijack the whole story. And the most outlandish of all is that the cold spot is the result of another universe colliding with our own.

The idea that our universe is not unique has been around for years, but is only now being taken seriously.

Part of the reason is that the theory of cosmic inflation suggests our universe is just one "bubble" of myriad universes that together make up the truly infinite universe, now rebranded as the Multiverse.

Attempts to create the long-sought Theory of Everything, describing all the particles and forces at work in the universe, also hint at such possibilities.

If our universe really is just one of a myriad filling the Multiverse, then collisions with our neighbours are inevitable. And the result of such collisions would be circular temperature anomalies - similar to the cold spot now seen by Planck.

The devil is in the details, however. Theories of these "cosmic bruises" predict ringlike patterns around these spots, like ripples spreading out from a stone thrown into a pond. Whether Planck has the power to see these remains unclear.

It is also possible that the gravitational field of the colliding universe will pull matter in our own universe towards it, creating a so-called "dark flow" effect.

Some theorists claim to have seen hints of this in earlier data, and they will now analyse the Planck data to see if there is any further evidence for it.

Further insights should emerge next year, when the ESA releases all the data it has, including measurements of the radiation able to reveal the presence of gravitational waves, ripple-like distortions of space and time expected when universes collide.

In retrospect, perhaps the ESA has done us all a favour by saying nothing about this. After all, we probably need at least a year's notice to get our heads around such an astounding possibility.

Robert Matthews is visiting reader in science at Aston University, Birmingham, England