The universe really is weird, which is bad news both for Albert Einstein and for would-be hackers hoping to break into quantum encryption systems.

Eighty years after Einstein dismissed the "spooky" idea that simply observing one particle could instantly change another far-away object; Dutch scientists said on Wednesday, 21 October they had decisively proved that the effect was indeed real.

Researchers of the Delft University of Technology detailed an experiment showing how two electrons at separate locations 1.3 km (0.8 mile) apart at the institute's campus demonstrated a clear, invisible and instantaneous connection. Their study is published in the journal "Nature".

Importantly, the new study closed loopholes in earlier tests that had left some doubt as to whether the eerie connection predicted by quantum theory was real or not.

Einstein insisted in a 1935 scientific paper that what he called "spooky action at a distance" had to be wrong and there must be undiscovered properties of particles to explain such counter-intuitive behaviour.

The idea confounds our daily experience of the world, where only local interactions causes change. However, in recent decades scientific evidence has been building that particles can indeed become "entangled", so that no matter how far apart they are, they will always be connected.

The Delft experiment is conclusive because, for the first time, scientists have closed two potential loopholes at once.

The first suggests that particles could somehow synchronise behaviour ahead of time, while the second implies that testing might detect only a subset of prepared entangled pairs.

To prove their case, the team led by Delft professor Ronald Hanson used two diamonds containing tiny traps for electrons with a magnetic property called "spin" and measured all entangled pairs across 1.3 km separating two laboratories.

Hanson said that the experiment not only puts an end to an 80-year-old debate, but also shows significant implications for the future because sophisticated cryptography is already using quantum properties to guarantee data security.

However, such quantum encryption systems will only be 100% secure, if all loopholes are closed as in the Delft system.

"Loopholes can be backdoors into systems," Hanson told Reuters. "When you go loophole-free then you add an extra layer of security and you can be absolutely certain there is no way for hackers to get in."