As of the moment of course zombies do not exist but could something like it arise, sure because humanity loves to try and play god
its impossible, humans brain is dumb
maybe they could do that in the future
Not fully, currently we do not posse the technology or knowledge to bring this horrific fantasy to a state of reality. For such a thing to happen would be completely accidently (mutation in mankind’s genetics or in the environment) or purposely (Genetic engineering or Bio-engineering; genetically altering microscopic virus or other organisms’.)
If you understand the human body and brain and organism communities; then you might realize that the possible of the real life creation of zombies isn't entirely impossible. How many different types of single cell organisms work together in our bodies to make us function, how many viruses and bacteria’s can grow within side us. Single cell organisms have a much greater chance of mutating then multi-cell organisms.
All that is required is a virus that replaces all common single cells organisms living inside the human body, including our brain cells. Additionally, a virus that can alter the DNA strains’ inside the body= hybrids such as seen in 'Left 4 Dead'
Note: my soon coming occupation will require me to understand all aspects of organisms, multi-cell, single cell, know every type of virus ever discovered, understand the cause of the virus, research possible ways to counter-act viruses, and figure out ways that new bio-logical weapons can be produced and create counter-measures for bio-logical attacks. So figuring out how each virus in each zombie movie works out is a fun creational way to dig deeper into the make-up of the human body.
No all single ceil organisms that live on our planet are from this planet. Meteorites’; at times will home extraterrestrial single ceil organisms.
Apparently a mutation of the rabies virus is pretty close to what would resemble a zombie virus... Kind of like what happened in 28 Days later.
Also, I was going to mention the meteors, but Foxyn88 beat me to it.
But, yeah... Earth's earliest life forms arrived on this planet via meteors... so I don't think its so farfetched that other organisms are still floating in space, and who knows what they could be.