How can UFOs travel to earth?

This is science-fiction fantasy based on our existing theories in physics with imagination.

How did the UFOs get to earth?

We have abundance of UFOs sightings recorded on earth. One might ask the question “how did the aliens get here with their space crafts?” That appeared to be impossible as the closest star to earth is 4 light-years away (one light-second is about 300,000 km). That distance is extremely far from earth, compare it to the intergalactic travel, the distance is even much greater, it would be billions of light-years, that is impractical for any type of space craft. The only scientific fantasy we can imagine is that these aliens must have travelled through a wormhole.

Space travel through worm hole

One school of thought of the physicists is that the universe is curved so space is curved, therefore the worm hole can form a tunnel with a short cut path to a very far place in the universe (See below picture).




The next question is how do the aliens find the right worm hole ? well they can make one. According to Einstein's theory of General relativity, we know a massive body can form curved space (See below picture).

                                                     

When the massive body has enough mass it can open up a worm hole to form a tunnel to the other side of space.


The trick is that how Aliens make a worm hole? Well they can make one based on Einstein’s famous equation E=mc^2. 

Where m= mass, E = energy and c= speed of light

This can be rearranged to form m=E/c^2. That is Energy and Mass are interchangeable. 

When aliens can manipulate extremely large amount of energy to a point in space then they can make a massive body like a black hole to create a worm hole. We know the amount of energy of a black hole is just one star. Aliens are likely to have the capability to harvest the energy of the entire star or even galaxy and manipulate it, then they can make a massive body like a black hole. Humans already have the technology to harvest the energy from the sun with solar panels by the technology of photo-electric effect, then collect and direct the energy to the consumption point, likewise Aliens probably have technology to harvest the energy of the entire star and galaxy and directed it to a point in space to crack open a tunnel to create a short cut like a worm hole.

According to Japanese physicist Michio Kaku, we are a Type 0 Civilisation which is capable of only harvesting energy from our own planet earth. Aliens on the UFOs are likely to be Type 2 Civilisation or above which capable of harvesting energy from stars and galaxies and manipulate it easily for intergalactic travel.

Sources :

Curved universe
https://en.wikipedia.org/wiki/Shape_of_the_universe#:~:text=A%20positively%20curved%20universe%20is,quotients%20of%20the%203%2Dsphere

Michio Kaku
https://en.wikipedia.org/wiki/Michio_Kaku

Type 3 civilisation
https://futurism.com/the-kardashev-scale-type-i-ii-iii-iv-v-civilization