If aliens exist, where would the closest ones be?

If we define aliens as life-forms native to another planet then, conceivably, the closest ones might be as close as Mars. If life is ever found there, though, it will be at best something comparable to our bacteria.

If you mean the typical UFO occupants, members of a putative technological civilisation capable of communicationg with, and travelling to, our solar system then the nearest star is Proxima Centauri. It is "only" 4.2 light years away. That is to say that light, which travels in the near-vacuum of space at some 186,000 miles per second, takes over 4 years to get here from there. The fastest speed ever achieved by a spacecraft from Earth was as recently as October 2018, when NASA's Parker solar probe achieved (briefly) a speed of nearly 156,000 mph. At that stupendous speed it would still take over 18,000 years to reach us from that star. Would intelligent creatures travel all that way just to bewilder a few people in the countryside, and then go home again?

And that's just our nearest neighbour. Most of the stars we can see in the night sky are some hundreds up to a few thousand light years away. Journeys to and from them would be measured in our geological timescales.

Aliens as some people imagine them might just as well not exist, for all the communication we can ever have with them. There may of course be intelligences thousands or millions of years ahead of us, in forms that we cannot imagine and which can achieve what we would consider to be magic, if we could perceive them at all, but again we would have nothing to say to each other.

That extraterrestrials exist is a conjecture, very likely but not yet proven.

The number of potential extraterrestrial civilizations is given by the Drake formula, which is the product of all the probabilities, to find planets at the right distance of its star, the right composition, etc. The first astrophysical terms are relatively well understood now, the biological ones less, and the spiritual terms (how civilisations evolve) are unknown.

I did an estimate of these probabilities in the VIII part of my book: extraterrestrial life, after more recent scientific data. For this we need to define a pseeimistic bound and an optimistic bound. In the vivinity of the Sun we find that the closest civilization may have apeared between 30 and 100 light years. This seems relatively pessimistic compared to previous estimates, the reason is that planets need a narrrow range of conditions to harbour life.

This distance is not easy for SETI, explaining that we did not found any yet.

The answer to your question requires speculation, since we have yet to prove the existence of aliens.

Based on that, I would speculate that the closest aliens would be walking right alongside you on the street. You can't tell the difference. They've probably been here walking among us for thousands of years.

On a more concrete level, the closest solar system to ours that I'm aware of is Alpha Centauri at around 4.5 lightyears away.

There's no proof life exists outside of Earth yet, so that would be the closest outside our solar system. We're still investigating the possibility of lower life forms in our solar system, but if we do find things like bacteria or even fish-like creatures, do they actually qualify as aliens? I can't answer that, so I guess that's where my speculation ends.

If aliens exist, where would the closest ones be?

Aliens are very rare. The nearest intelligent Aliens are on a planet that is 500 million light years from here. If their starship could travel through space at half the speed of light, they could be here in a billion years.

What is the easiest way for aliens to destroy humanity without destroying Earth?

Well...lets say history repeats itself. Like in the French and Indian war, part of it was one by the spread of smallpox. Aliens, probably being immune to viruses on their own 'planet' could easily use a smoke bomb or even blankets carrying their own genetic viruses in a busy place; New York. Disease would spread quickly. Sooner or later

What is the Tikona broadband?

You may read this to start - How do I raise a consumer complaint against Tikona Digital Networks?. You may even read my review here - I am receiving bills for my broadband service (Tikona digital) even when I requested my ISP to disconnect it. Where can I lodge complaint?

Can we throw our rubbish into space?

Short answer, yes. But it would be a really expensive wait to do it. The bigger problem is that now instead of the garbage just sitting there causing a mess, it is now traveling at over 17,000 mph (27,000 kph).