Polygraphs are fundamentally flawed because they measure physiological stress responses (heart rate, sweating, breathing) rather than deception itself, but newer fMRI studies looking at actual brain activity patterns during deception are way more promising since they can detect specific neural signatures when someone constructs a false narrative vs recalls a true memory.

Not really, because it's not measuring if you're lying or not, it's measuring a stress reaction.

So if lying is like breathing to you (cough, Trump, cough) you can pass the test with flying colors.

OTOH if just the idea of a test stresses you out, it will say you're lying about the color of the sky.

No. You can't change astrology either to make it real.

I think you can pass it if you ate chipotle right before the test, and the urge to go to the bathroom will normalize all the lies you tell

It's theoretically plausible that you could map someone's brain thoroughly enough with fMRI to be able to detect when they're lying with some modicum of confidence, but that's going to be a pretty huge process (and your actual accuracy will always be debatable and it will be difficult to raise above a reasonable doubt).