Time travel conspiracy !?

When i'm talking about time travelling i'm not talking about those popular movies like looper.

Or stewie from family guy.

No, I actually mean time travelling !

Time is everywhere if you like it or not but is it possible to manipulate time to go back & forth !?

Time travelling!

Back when kennedy got assasinated they received a call with someone telling them what was going down the place the time and all the necessary information.

Note: this happened before the actual assasination and they didn't take it serious.

They tried to trace the person but she / he was never found again as if she / he dissapeared from the globe.

Now we all know about the gouverment and their power.

If they wanted to find someone they wouldve had no problems UNLESS the person wasn't from that time and came here to warn us.

Some people also believe that donald trump is actualy John smith if i'm right who is from the future and came to warn us for what would happen.

But what if the gouverment know this and when something is happening what they don't like they just go and change it.

There is one thing we learned from these movies and that is altering the past is never EVER good.

This however would prove us that there are multiple dimensions since if altering the past has no visible changes for our present time.

However when for example they could prevent kennedy from assasinated they just had to hide him and fake his death on the same way.

Changing the past should have visual changes for the present sometimes even VERY BIG changes but what if you time travel not to alter a specific event but for example hide a cure for cancer as example.

It wouldn't realy change alot would it !?