In the world of cosmology, the latest scientific evidence has revealed that 85 percent of the universe is made up of dark matter. We can't see it, but it is definitely there. The equations tell us it must be, for nothing else explains the visible effects of mass on the universe.
Something similar can — cannot? — be seen in eastern Ukraine. Russia's direct involvement is barely visible to the naked eye, but it can be discerned through examination of the evidence. No other explanation is plausible.
Russia is the only force with de facto control over border areas in Donetsk and Luhansk at present and it is demonstrably true that Russian citizens are crossing that border to fight in Ukraine, indicating that at the bare minimum Russia is letting this happen or that its border guards are incompetent to an improbable degree.
The "pro-Russian forces" operating in eastern Ukraine are precisely that — units doing Moscow's bidding with Moscow's backing. Their interests and those of the Kremlin are more or less aligned, although is conceivable that some of their followers do not even know they are the Kremlin's puppets.
In addition to military proxy forces, the Kremlin is also using rhetorical proxies for the things that even President Vladimir Putin cannot say. In Russia he can turn to Aleksandr Barkashov, Leonid Slutsky, Sergei Glazyev, Sergei Markov and even Ramzan Kadyrov in Chechnya either to raise the stakes, or, as the occasion demands, to give the impression that he is a relative moderate. In Ukraine he has separatist leaders in the shape of Alexander Borodai and Igor Strelkov whom he can support or admonish whenever it suits.
However, Putin speaks the truth when he says he does not fully control them all, in part because doing so would mean taking responsibility for them. Putin has always regarded the uncouth with distaste, as he does now with Strelkov and Borodai. They are useful, but they can be embarrassing, and indeed incriminating.
The more direct forms of the Kremlin's involvement are often covered up by a Russian intelligence service working overtime. What we know already is astonishing. Imagine what we do not know. What is certain is that Russia's GRU, or military intelligence, has strong connections with and infiltrations into its Ukrainian counterpart, built up over many years. The Russians have never really trusted the Ukrainians — even in Soviet times — and the Black Sea Fleet's presence on Ukrainian soil was a key source of espionage.
Hardware used by pro-Russian forces, including uniforms, vehicles and weapons, is often alleged to be of Russian origin, sometimes rather excitedly so by patriotic Ukrainians and leaders in Kiev. Quite possibly much of it is Russian, but there is little direct evidence. With about 5,000 separatists fighters currently in Ukraine's eastern regions, ranging in origin from Chechnya to Crimea, it is impossible to disentangle what has been supplied and what purloined.
But as noted, the border is largely open and hard evidence of infiltration of Russian equipment is overwhelmingly obvious to everyone in NATO and the Western national intelligence services. Ragtag separatist "citizens" do not have access to anti-aircraft missiles and other precision weaponry, let alone the training to use them — especially as they are by and large too young to have received Soviet training.
Like the business world, the separatists war is built on networks rather than command structures, and is therefore confusing to people who are used to Western military practice. If the Ukrainian forces succeed in controlling the border, the main aim of operations now, they will be able to put a stop to it.
But Russian involvement in Ukraine is far more than tanks and soldiers. Modern warfare is a toolbox which includes conscription via social networks, propaganda via television, coercion via bribery and threats, pressure via the Russian Orthodox Church, blackmail via energy and disruption via cyber attack. Again, some of these are self-evidently from Russia. Others have to be discerned through examination of the circumstantial evidence. Who benefits? Who has the resources?
As in the case of the Crimea operation, mainstream media, and consequently Western governments, have been reluctant to assess the evidence of weapons, equipment, and individuals which undoubtedly come from Russia, perhaps through a misguided trust in Russian assurances that they are not; perhaps because they fear the intricacies are too technical for their readership's short attention span. Thus, once again, it is left to informed experts to document the direct evidence.
Perhaps the final piece of evidence should be supplied by Vladimir Putin himself. It is he who believes Russia and Ukraine are one nation; it is he who said last week that it was Russia's duty to defend ethnic Russians abroad. With that central belief system it would be astonishing if there were not Russian involvement in eastern Ukraine. It is not worth wasting time considering direct denials by Putin and other Russian officials, since the experience of Crimea shows that they are both worthless and temporary.
The case for a more robust policy against Russian meddling in Ukraine can thus easily be made by Western media and governments, but only if there is the will to do so. Based on publicly and privately available intelligence, it is now beyond any reasonable doubt that Russia, in one way or another, supports the separatists. And if we're not making decisions based upon the evidence, what are they based on? In fact, what then is the point of having a foreign policy at all?
James Nixey is the head of Chatham House's Russia and Eurasia Program.