Explain how the exhaust will cool to background radiation levels.
The assumption here is that the exhaust is in the form of a gas. Once it passes through the constriction of the rocket nozzle, it expands (the effect is to turn thermal random motion of the particles of the exhaust into directed velocity). Expansion of a gas causes cooling. After leaving the bell, there are no more restrictions to expansion of the gas aside from the small amount of matter in space.
In addition, the much increased surface area of the exhaust plume allows for greater radiation of heat to space.
That is what you posted. And they will take 300 years to reach the Oort cloud.
And again, so what? I already explained why I posted that. No one is going to use the behavior of Voyager spacecraft, particularly beaming a highly directed signal at the target you're trying to sneak up on, as a strategy for stealth. It was an inappropriate example for the article to use. That's the only reason I mentioned it.
You claim that a cloak of invisibility is possible.
I say that physics says it is not.
Then use physics to make that argument not assertions that I brought up Voyager. And please characterize my arguments correctly. I'm not saying that invisibility is possible, but rather that stealth is.
I say that if it was an invisibility cloak you wouldn't need tactics to take out anyone who isn't blind. The cloak would make you invisible. They would not see you. Tactics do not beat physics.
I think you're starting to see my point. Stealth isn't perfect. It would be relatively hard against large, sensitive detectors. But you can't haul those on a high acceleration warship (unless you're doing some sort of swarm-based sensing). Disable the detectors and you're left with far weaker systems. The methods we've been discussing would be much more effective in that case.
It's also worth noting that even rudimentary stealth efforts might be effective against self-guiding weapons or enemies who don't happen to have access to good sensory equipment. It can provide an edge or improve survivability.