The idea of a time machine that allows you to go back to when the machine was created is not apparently forbidden by the laws of physics (see <PERSON>'s answer above).
The technique is based around an accelerated worm-hole, which works as follows:
* You make a worm-hole, so it has two ends; S (stationary) and A (accelerated).
* In the year 2020, A gets accelerated to near-C, cruises for a bit, then slows back down to "rest". It goes in a curved path so that it comes back close to S.
* Assume that for S, this whole escapade took 10 years so S's clock shows 2030. Note that S has been in existence for 10 years, calmly waiting for A to come back.
* For A, because of time-dilation the trip took 1 year so A's clock reads 2021.
* Because of the way time connects through the wormhole, if you now enter A (in the year 2030), you will pop out of S in the year 2021.
So you now have a pipe connecting 2030 to 2021 and can jump back and forwards through time as much as you like.
Although this doesn't appear to violate any physical laws, it does create a few paradoxes:
* Causality paradox: You go back to 2021 and meet yourself, 9 years before you're due to get into the worm-hole. Future-you shoots Past-you. Future-you jumps back to 2030. 337
What happens to all the experiences you had (in the original timeline) between 2021 and 2030? How did future-you jump into the worm-hole the first time anyway, since you had been shot in 2021? Has anyone seen Looper?
* Information paradox: You take your iPhone 11 from 2030 back to 2021. It doesn't work very well since there is no 6G network. You give it to Apple. They copy it without having to do the research that created it in the first place.
* Energy paradox: You unplug your fully-charged tritium niobate battery from your car in 2030 and bring it back to 2021. Once you hook it up, you have free electricity for a year. Where did this energy come from? Admittedly, 2030 has lost the 1.21 Gigajoules your battery contains but does conservation of energy really hold over time?
I truly have no idea where that leaves us... 434