So the people of the future are too stupid to understand the awacs concept where specialized craft have a big active sensor and route the data to the whole fleet
Specialized AWACS craft may be in - with massive *passive* sensors (alternatively, high-res situational image synthesized from information provided by very large cloud of cheap, networked, tiny drones, with cheap, shitty sensors working in concert might be used). You can't get around the speed of light and you can't get around inverse square, plus you will see anything you want using passive sensors without emitting conspicuous pings to prevent anything you might have somehow missed otherwise from missing your already very obvious heat signature by adding BRIGHT radar blinker to it.
AND too stupid to shield their ships against IR, which will be necessary for any effective nonmetal armor anyway.
Yes, I fully expect they will be too stupid to circumvent the whole fucking thermodynamics and not radiate anything detectable from even their crew section, let alone fucking reactor.
Anyway, instead of wasting my breath explaining physics to you, I'll just link you to someone who already did and did it much better than I ever could:
http://www.projectrho.com/rocket/spacewardetect.php
For somewhat plausible space combat scenarios not involving RKVing the fuck out of everything, that also include disguise, if not outright stealth, I'd go here:
http://www.rocketpunk-manifesto.com/2009/06/space-warfare-ii-stealth-reconsidered.html
And why do their IR sensors work at relativistic speeds?
And why the fuck not? Detecting radiation blueshifted from far IR into near IR or even vis is going to be even easier.
I'm trying to get draq to elaborate..
Read what I quoted again. I've made some minor, hopefully recognizable alterations.
You can't keep your codexian monocle in regards to RPGs if you go full biodrone on other genres.
Actually, stealthy radar has been invented, it is called low probability of intercept (LPI) and is operationally used today on aircraft like the F-22.
Stealthy in relatively noisy and cluttered Earth environment is not the same thing as stealthy in space.
Same if you replace "stealthy" with "useful" and "relatively noisy and cluttered" with "excessively small and close packed".
If it's active it's distance squared easier to detect (using undetectable passive means) than it is to actually use.
And it will be detected distance/c earlier than it will provide any sort of data.