To someone in 1850, the concept of the atomic bomb, a technology that would give humans the power to end all life on earth, would have seemed unfathomably more advanced than their understanding of human capabilities.
If a government invented the Newcomen steam engine, but kept it secret... what would happen?
(a) There would have been far slower development, because as many ideas wouldn't have been tried, because it was secret.
(b) There would have been mysterious black box engines wherever it was used, or power sheds with big DO NOT ENTER signs.
Point being, you can't have a secret technology AND have it develop at the pace of an open technology AND use it.
Specifically for aerospace/engine applications, the government would use the craft for... what?
Can't fly it where it might be shot down. Can't fly it over populated areas. What the heck do they do with it that's useful?
Considering the years of first flights, not to mention initial design and construction work, that seems rather advanced for the times, certainly looking inconceivably alien to any outsider. And would continue to do so during their hey-days of operation.
They'd still be useful today, but there are other options availabe now, which can compensate to fill that gap, though there are people saying still not fully.
Now? If you're running a secret program, eventually it turns up.
See almost certain RQ-180 photos: https://www.forbes.com/sites/davidaxe/2021/09/07/americas-ne... https://aviationweek.com/defense-space/aircraft-propulsion/p...
The idea that there's a physics-breakthrough craft / technology out there, in active use, just isn't plausible.
... unless it's invisible?
But the UFO crowd (surprisingly?) doesn't seem too eager to accuse the government of having invisible craft.
That's just a temporary gap in coveruppage. They will just be tagged 'Do not snap!' cybermagically, and all the locked down gadgets will comply!1!!
US politics don't seem more hawkish/fear mongering than normal. China is hesitantly ready to invade Taiwan. Russia can't win a war against a much smaller power.
I think these things would be different if some people knew I could change mass of objects like that -- Think of the ballistic implications!
Basically, if we are soon able to accelerate at 5000g, then interstellar flight is quite possible. In which case I would like to see the suns set on a world orbiting binary stars, please.
Keep it as an ace up your sleeves?
1. If you keep it very strictly hidden, development will be slow and based on the zietgiest comment above, you are at risk of your enemy discovering the same technology by chance and completing it one unit of time before you. So you must work as fast as possible even if this risks some leakage.
2. If you have worked in secret and somehow perfected a technology, it will manifest itself in your negotiations as your negotiation style or forcefulness will likely change given your perception of comparative position or bargaining power. We have not observed a drastic change in global geopolitical order to support this claim so it is unlikely someone has an ace up their sleeve. Not saying it is impossible, sometimes people do show discipline just saying it is unlikely based on the other comments on this thread.