At 99% the speed of light you could get to Mars in 30 seconds from *your* perspective, when Mars is (about) closest to Earth

Observers on Earth however, would see you take 3 minutes 30 seconds

THAT is time dilation, it really happens, this is a fundamental aspect of reality.

When something reaches light speed it doesn't experience time passing at all — it's the extreme end of time dilation. If you left Earth and could somehow accelerate to near light speed, you could navigate the cosmos in far less time, but everyone back home would be aging...

... e.g. at 99.9% light speed it would take you about 73 days to reach the nearest star Proxima Centauri (4.247 light years away), but by the time you get there everyone on Earth would have aged 4 years and 90 days

Why not have a go yourself? Here's an online calculator, just enter the speed and see how much time is reduced for you.

The time elapsed for you the traveler will return as a percentage https://www.emc2-explained.info/Dilation-Calc/#.YBl5y-gzb-g

So clearly @30SECONDSTOMARS is traveling at 99% the speed of light

All of this assumes a lot, obviously. I mean, accelerating to that speed, then decelerating so you can arrive safely... having the fuel to do it... not hitting meteoroid on the way and so on. Pretty convenient that time slows down for the traveler though, I think...

Relativity is a real mind bender. I recommend this video: by @thephysicsgirl

Also regarding the Twin Paradox... more info here (it's a good write-up) -- https://en.wikipedia.org/wiki/Twin_paradox

Some great replies explaining more about the implications e.g. https://twitter.com/MattWoodTX/status/1356647965050474496

and.. https://twitter.com/th13r85/status/1356647942581551105