Would We See the Aliens Coming?

universetoday.com ^ | on June 1, 2015 | Fraser Cain

[BenLurkin]

A basic rule of the Universe is that you can’t go faster than the speed of light. So I’m going to have any aliens trying to attack us traveling at sublight speeds.

So, we’ll say they’ve got access to a giant mountain of power. They can afford to travel at 10% the speed of light, which means before they get to us, they have to slow down. At this speed, deceleration is expensive. We’d see the energy signature from their brakes long before they even reached Earth.

Let’s say they’re passing the orbit of the dwarf planet Pluto, which is 4 light-hours away. Since they’re travelling at 10% the speed of light, we’d have about 40 hours to scramble jet fighters, get those tanks out onto the streets and round up Will Smith, Jeff Goldblum and Bruce Willis to hide behind.

...

We’re actually pretty good at detecting heat with our infrared telescopes.

A space drive decelerating a city-sized alien spacecraft from a significant portion of the speed of light would shed a mountain of heat, and that’s all heat we might detect.

...

If aliens wanted to catch us off guard, they can use one of the oldest tricks in the aerial combat book, known as the Dicta Boelcke. They can fly at us using the Sun as camouflage. A rather large portion of the sky is completely obscured by that glowing ball of fiery plasma.

...

Astronomers often discover asteroids skimming by the Earth just after they’ve just gone past. That’s because they hurl at us from the Sun, just like clever aliens.

To spot those asteroids, we’ll need to deploy a space-based sky survey that can watch the heavens from a different perspective than Earth. Plans for this kind of mission are actually in the works.

[no-to-illegals]

sort of like Samuel Clemons, as in repeating oneself ... ?

[no-to-illegals]

kind of like the Ark of the Covenant ... ?

[piytar]

Why would anybody want to come here? :-)

That's actually a good question.

Maybe a safari? See the natives?

I laugh at the movies where the aliens come here for some natural resource. If any aliens are part of an interstellar space-faring civilization, there is literally NOTHING on this ball of dirt they can't get from uncountable other unoccupied places. NOTHING. Certainly nothing worth launching an invasion over.

At best, we might be a tourist attraction...

[piytar]

It’s not. There are gigatons of water just in comets. And that’s just in our local solar system...

[no-to-illegals]

Creek also corrected me ... am standing, in the seated position, corrected.

[piytar]

Sorry, did not mean to be snarky. Just factual...

[no-to-illegals]

did not consider your remark ‘snarky’ ... If that was ‘snarky’ I’ve never been factual ... ;^)

[Georgia Girl 2]

Well or if their planet has had economic collapse and they need welfare. :-)

[Political Junkie Too]

Since we'll all be underwater in submerged cities because of global warming, maybe the aliens will think that nobody's here and just pass us by.

-PJ

[Little Ray]

Assuming sublight, yes.
We will see an infrared spike from the launch site, and maybe approaching us. We will see another one when when they start breaking.
Assuming we ‘re looking, which ain’t that hard. We have the capability to do a “whole sky” scan every night in every hemisphere if we want to...
Depending on the aliens intentions, there may be a separation before they start braking. Hostile aliens will drop waves of bombardment vehicles before they start braking. that will pass through the solar system close to Earth and drop small projectiles to impact targets on Earth a substantial fraction of the speed light. A second wave will do bomb damage analysis and third wave will finish off what the first missed.
The good news is, if we pay attention, the velocity works both ways. At the speeds they are moving, we could probably destroy their bombardment vehicles with styrofoam cups if we could get them positioned in the right place (even a styrofoam cup is going to hurt at 30K KPS). Of course we could use more capable kill vehicles, too (blocks of iron are good...).

[Little Ray]

There will be heat - if not from the drive then from the power plant. Conversion of fuel into power is never perfect, and the process will always create a substantial amount of heat.

[Little Ray]

The Marines would die horribly when they ran out fuel and ammo, which would be pretty quick.

We are talking one hell of a supply line if aliens are invading and starting a shooting war.

More likely they would deal with humans as a pest control issue - engineer a human-specific disease, and let fly. Or hit us a with a bunch rocks at 10% C and clean the survivors.

[Phlap]

Why,would any self respecting alien come to this obscure planet in our obscure galaxy? After all water is everywhere according to NASA, so what do we have to attract them to us?

[mabarker1]

I'm ripping off Yer Pic;)

[dr_lew]

“Any sufficiently advanced technology is indistinguishable from magic”. R. Heineken.

... Arthur C. Coors, I believe :-)

[Greysard]

There will be heat - if not from the drive then from the power plant. Conversion of fuel into power is never perfect, and the process will always create a substantial amount of heat.

This conversion, as opposed to the jet exhaust, can be radiated away from the travel path. Some types of fuel generate little to no heat within the engine - a charged ultracapacitor is one example of such "fuel."

Really, humanity doesn't have a usable star drive technology, and we can't say much about what is possible. It's like saying in 1850 that "If someone invents a flying machine, we will clearly see it in the sky by the cloud of coal smoke that its steam engine produces."

[tumblindice]

‘Enders Game’. We’ll just Shanghai some pubescent JDs from online war gaming rooms and train them to defeat the Formicans in one fell battle.
The rest of us can kick back with beer and BBQ ‘cause the little rodents won’t even know it’s all real.

[MHGinTN]

The speed of light is much slower today than a billion years at. It is related to the increase in zero point energy as the Universe expands.

[Vaquero]

Not an astrophysicist (or any other type of trained scientist)....nor do I play one on TV. Just an interested bystander of the universe. I hate to resort to Wikipedia (yeah, it is flawed ) but: "According to measurements, the Universe's expansion rate was decelerating until about 5 billion years ago due to the gravitational attraction of the matter content of the Universe, after which time the expansion began accelerating. In order to explain the acceleration physicists have postulated the existence of dark energy which appears in the simplest theoretical models as a cosmological constant. According to the simplest extrapolation of the currently-favored cosmological model (known as "ΛCDM"), this acceleration becomes more dominant into the future. While special relativity constrains objects in the Universe from moving faster than light with respect to each other when they are in a local, dynamical relationship, it places no theoretical constraint on the relative motion between two objects that are globally separated and out of causal contact. It is thus possible for two objects to become separated in space by more than the distance light could have travelled, which means that, if the expansion remains constant, the two objects will never come into causal contact. For example, galaxies that are more than approximately 4.5 gigaparsecs (14.7 billion light-years) away from us are expanding away from us faster than light. We can still see such objects because the Universe in the past was expanding more slowly than it is today, so the ancient light being received from these objects is still able to reach us, though if the expansion continues unabated, there will never come a time that we will see the light from such objects being produced today (on a so-called "space-like slice of spacetime") and vice versa because space itself is expanding between Earth and the source faster than any light can be exchanged."

[uglybiker]

They’re already here trimming my neighbors trees.