How much time would we need to take on...

[Darth Tedious]

@Purple: Of course, we have to assume these laws of physics would work for us, otherwise all of their stuff stops working when they bring it over. Then we'd win by default.

Stupid space wizards! There's no such thing as the Force!
Everybody knows hoverboards don't work on water.

[Purple]

@Purple: Of course, we have to assume these laws of physics would work for us, otherwise all of their stuff stops working when they bring it over. Then we'd win by default.

Not really. The op clearly contradicts that:

Assuming this, and based on the laws of physics that we know, including theories that contain a decent amount of evidence supporting it, how many years of development will it probably take for us to be able to survive an invasion by:

The only conclusion I can make from this is that the magical things from other universes (warp drive, phasers, hyperdrive etc) work for them and not for us. Otherwise the situation would be rendered: a) meaningless as we win by default or b) in violation of the OP.

[Luke Skywalker]

The purpose of this thread is to see if pure hard sci fi has enough potential to conceivably defeat soft sci fi heavyweights.

[doom3607]

The answer is no. The Empire calls out the Death Star, Sun Crusher, insert-a-superweapon-any-superweapon...

[PREDATOR490]

Command & Conquer - Has production capabilties that can make tanks in seconds with the only resource required being Tiberium deposits. Give GDI enough $$$ and they can mint out men, weapons, ammo and vehicles in quantaties that would overrun a conventional battlefield. GDI would have to bring Tiberium with them to fuel their production and the destruction of a Tiberium Refinery would spread the stuff into the environment. Even if a victory was achieved, the introduction of Tiberium to our planet is going to gradually destroy the planet making it a hollow one at best.

That said, GDI are a defense initiative by default designed to protect THEIR Earth. They do not possess intergalactic technology to invade other planets nor the desire to do so. Making them do so would be forcing them into having technology and a behaviour that has never been observed. If it is on OUR Earth then the Ion Cannon Network and orbital space station will have to be reassembled before they can be deployed along with MCV beachheads. That should provide a window that even modern day technology could sufficiently exploit.
Detection might be a problem depending on how GDI go about it, if they are smart they would lay low and build a covert beachhead before marching to war.

NOD - Would be far more dangerous as with their use of more advanced technology than GDI at points. The inherant stealth technology they use could make detection of bases or their vehicles difficult or impossible until they have already established the foothold required. Then again, NOD is more likely to use subversion and shadow play tactics rather than engage in open warfare.
NOD by default have been fighting the far larger and better funded GDI military for decades thus wont be so eager to take on an entire planet. Although the spread of Tiberium into the planet becomes guranteed if NOD are granted enough time.

Reapers - Unknown

Mass Effect 3 Trailer 1

Mass Effect 3 Trailer 2

When the natives of this planet develop biotic potential, access to Mass Relays and Prothean legacy items... we might have a chance. Otherwise Earth remains entirely fucked until such a time we have weapons or ships powerful enough to fight them. Without Mass Effect magi-tech thats going to take a lot longer than it did in the game.

Wait until next year when the Reapers actually arrive in person and their own capabilities can be observed. Currently the only information to go through is limited and done via third parties like the Collectors, Geth or Saren. From those abilities the Reapers can potentially unleash lethal plagues, indoctrination or simply sit behind the lines manipulating the planet via MORE third parties.

[Luke Skywalker]

About C&C, the last time I checked (I only have 3 and have hardly played it at all), they possess railguns that can kill soldiers through concrete and various other borderline wank weaponry that could take far more than a few decades to surpass. In fact, there were literature-based calculations that penned orbital platforms to be in the gigaton range.

As for the Federation, I'd disagree that they cannot be beaten in space. However magical some of the technobabble may be, they still have finite limits. For example, their photon torpedos have finite yields that can be surpassed by real life theoretical antimatter warheads, and their shielding systems have finite power that can be overwhelmed.

[Purple]

In fact, there were literature-based calculations that penned orbital platforms to be in the gigaton range.

The only thing I can think of that would qualify for those levels of damage is the liquid tiberium blast in C&C3 and that was pretty much them hitting a giant LT stockpile and not the effects of the ion cannon blast.