Premature panic, perhaps.
If somebody somewhere has FTL travel, they'd probably be here already. If nobody has FTL travel, about all we can do is try to talk by radio, with a lot of lag.
You don't need FTL travel to get here. All you need is interstellar travel at sub-luminal speeds, and a life span that makes it reasonable to undertake the journey from your home-world to the Earth.
Say, a species with a lifespan of ten thousand years living in a planet 10 light years away, that can travel at half the speed of light- it would take them 20 years to travel here and 20 to go back. For us, half a life-time. For them, just a short hop. And probably totally worth it if there was a habitable planet at the end of it.
Can we really say what is the expected life span of intelligent species with technological civilisations on planets in a 10 light years radius from us? Like hell we can.
Note also that with that kind of speed they'd be here within the lifetime of most people currently alive (even taking into account the 10 years it would take for SETI's message to reach them). Even with a quarter of the speed of light, many of us would be still around. We're not even talking geological time scales here. We'd have plenty of time to reflect on our foolishness. That's no way to go extinct, cursing at your species' stupidity.
If you won't listen to prof. Hawking at least listen to Hawkwind: Space is deep. Don't go fucking with it.
You can even relax this requirement if you're willing to consider generation ships: https://en.wikipedia.org/wiki/Generation_ship
Those are just silly popular Sci-fi series scenarios and already they do to "You Need FTL to Attack the Earth" what the Vehrmacht did to the Maginot line.
We can't be debating SETI's happy-go-lucky talk-to-aliens plans at that sort of level. These guys need to be reminded, we may be alone in the universe but they're not alone on this planet. Even if there was no risk at all, unilaterally deciding to try and contact an alien species on behalf of all humankind is insanely irresponsible.
I would say pointless panic. The paper itself makes the point that if there is intelligent life elsewhere in the universe that is capable of coming here to Earth, it is going to be millions of years (or more) ahead of us technologically. That means we would be at the mercy of such beings if they came here. But it also means we have already betrayed our presence to them, whether we make SETI broadcasts or not; we have been broadcasting radio and TV signals that, to such a species, will clearly indicate intelligent origin for about a century now. So the instant such a species comes within 100 light years of Earth, it will know we are here. There is nothing we can do about that, and draconian restrictions on further broadcasts will not change it.
Any sufficiently advanced civilization would supercede lesser ones. Even if contact would be limited to prevent any cultural leakage the knowledge of the existence of intelligent life will lead to collapse of at least 3 major religions and their cultural frameworks.
Aliens might know we exist but they might have rules against visitation unless being invited first. Individuals that send powerful invitations can be seen as putting the earth and human civilization as we know it at risk.
Religion isn't that vulnerable to rationality. Christianity has survived Copernicus, Martin Luther, evolution, the Dead Sea Scrolls, and 2000 years of Jesus Christ failing to show up as promised.
I think that's true, but it doesn't change anything I was saying.
No.
If you include "believed to be impossible" in the definition, I guess.
I know, I know, it's space opera stuff.
How would that change anything? You're still sending matter or energy FTL; you need matter or energy to curve spacetime.
I'm not even sure they are distinct except in mode of perception. They may both be emergent properties of a universe that is a) functional and b) lazily evaluated.
Does faster than light mean instantaneous? Is there no "speed limit" (that we know of) above the speed of light?
No. But as far as we know, the speed of light is an absolute speed limit.
Objects can move relatively at greater speeds than light when you account for the expansion of the universe.
Other hypothetical modes of transportation such as wormholes, hyperspace or quantum slip space allow you to take shortcuts but often there will be travel time involved.