Why Do Metals Bond in Space? Investigating the Casimir Effect

[RisingSun361]

I was drinking a bottle of tea the other day, and I noticed the cap had a claim that two metals of the same type will stick together in space. Why is this?

Edit: "Why" do metals...

 

[Orodruin]

Likely a reference to cold welding.

 

[Borek]

Or to a Casimir effect.

Even if it doesn't require two pieces of the same metal, actually any two objects will do.