If the Borg possess the ability to time travel as we have seen, why would they travel in space to their target (i.e. Earth) then back in time, could not they do it from the Delta quadrant? That is move back in time in the delta quadrant and then travel to any planet to assimilate. No combat, battles or anything. Or would that create paradoxes?

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    One possibility may be that the Borg did not have their network of transwarp conduits in the late 21st century. This would have meant that they'd need to travel across the galaxy using normal warp, which would be roughly a 70 year trip. Still doable, by Borg standards, but open to many more variables.
    – Xantec
    Commented Dec 26, 2012 at 18:38
  • related: scifi.stackexchange.com/questions/887/…
    – DampeS8N
    Commented Dec 26, 2012 at 20:05

5 Answers 5


The novel Engines of Destiny provides a possible reason. From Memory Beta on Species 1429:

From 1429, she gained the time travel technology that she utilized aboard the Borg sphere that traveled back in time; however, the device malfunctioned - where she had set it to take her only a few days in the past, it returned her several centuries. After this, the Queen decided that she would only utilize it in an extreme emergency, as to prevent further malfunctions.

The movie First Contact opens with a battle against a Borg Cube, which is destroyed. The Sphere detaches and goes back in time as a last-ditch effort as the Cube is destroyed. This (non-canon) quote provides a possible reason - although it's not clear whether or not the sphere that Memory Beta refers to is the one from First Contact, or another one the Queen was testing the technology on.

A couple days may well have been the intent of the Sphere from First Contact; it could have contacted the Cube before it was destroyed and altered the outcome, without major changes to the timeline, which wouldn't necessarily have been a desired outcome for the Borg considering the numerous conflicts they've already had.

(Aside, preventing humans from reaching space before the Federation was created would have been quite a bad mistake on the Borg's part, since their conflict with Species 8472 would likely have already started by that time (Scorpion takes place on Stardate 50984.3, and First Contact on Stardate 50893.5). If there was overlap between Voyager's assistance and First Contact, their primary goal would've been to destroy the Federation after Voyager arrived in the Delta Quadrant. This also would explain why the Borg in Regeneration didn't stay on Earth and try to assimilate the planet...)

  • Yes, but if they had assimilated earth before voyager, the borg sphere that traveled back in time would have the information about 8472 and Voyager even if the rest of the borg collective doesn't when they return to the 24th century, right? Just like spock(Nimoy) in the new movies retains the information he has even though he's traveled back in time and the timeline has changed and the new spock/kirk is on a very different path. Nimoy still remembers everything about Khan even though none of it ever happened yet.
    – JMFB
    Commented May 8, 2015 at 6:43
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    @JMFB Time travel in Star Trek works in a multitude of different ways depending on circumstances. In the 2009 movie, they split off and created a new timeline instead of altering the existing one, while the change to Earth in First Contact before the Enterprise went back indicates the timeline was changed, not split
    – Izkata
    Commented May 8, 2015 at 12:58
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    and the difference between split and change is?
    – JMFB
    Commented May 8, 2015 at 16:00
  • @JMFB See In Star Trek (2009), Did the Original Timeline Survive?
    – Izkata
    Commented May 8, 2015 at 16:02
  • Thx for the link. I read it and am more confused than before. The answers make no sense other than, ST is not consistent, they wanted to reboot the series, etc. etc. But if somebody travels back in time, they are traveling back in their own timeline, right? So it would affect them.
    – JMFB
    Commented May 8, 2015 at 16:23

The Borg are both patient and logical. They are also cautious. Time travel is dangerous - you run many risks in attempting it. You could change things to make the future significantly worse for you.

Consider the Borg that visited the past - they were in a single Borg Sphere. There were very few drones and the Borg Queen. The humans on the planet were recovering from a war. They had weapons aplenty, and were not shy about using them - they'd had plenty of practice.

Eventually, to conquer the planet, the Borg would have to land and/or transport. This opens them up to the chance of violence. The humans were well-versed in firearms, and could have killed drones by the dozens. There's also a strong chance that the humans could piggyback on a Borg teleport to get back to the ship. The chances are low, but there. And with armed humans on the ship, the Queen would be vulnerable.

Time travel was the Borg's backup plan. They didn't really want to go back in time and have two Collectives - one in Delta and one in Alpha. They had strong reasons to believe that the Cube would reach Earth, and could easily have begun assimilating Earth without time travel had they succeeded (which, mind you, they very nearly did). The Sphere was their backup plan, in case something stopped their Cube.

One could expect that this is a standard methodology for the Borg when confronting a species with technology that makes Borg defeat possible. First, try for an outright military victory. In the event that it fails, send in a second Cube some time later - the second Cube could smash defenses that had been crippled by the first, and have a time-travelling Sphere ready in the event of the second Cube's destruction.

It is obviously in the Borg's best interest to assimilate a species at the latest possible point - each species brings unique technical and/or cultural capabilities. Assimilating Earth in the late 2000s would not gain the Borg access to any of Starfleet's advanced technologies, some of which could have been useful to the Borg.

  • Yes but the assimilation wouldn't work like that, and you see that they were successful. When the enterprise got to earth the entire planet was Borg.
    – JMFB
    Commented May 8, 2015 at 6:53
  • Assimilation wouldn't work like what, @JMFB? I did watch the movie, and saw the same scene - after the Sphere's initial time displacement, the Earth was assimilated in the past. I don't contest it - the targeted time period was ideal for Borg assimilation, though still risky. The gains, however, were less than they would have gotten from assimilating Star Fleet's Earth.
    – Jeff
    Commented May 8, 2015 at 12:31
  • I agree that the gains would be less, for sure, hundreds of years of colonizing the galaxy. But the would assimilate it one piece at a time, their numbers would grow as more drones were created, allowing for more drones. More drones means more rounding up and assimilating. This is actually a good question.
    – JMFB
    Commented May 8, 2015 at 16:04

All of the above answers are good, but I want to add one more factor: the Federation's pre-existing infrastructure.

The Borg were able to rapidly assimilate the Enterprise-E because it functioned on equivalent technology. But imagine the Borg trying to assimilate us now, or during World War II, or during the Roman Empire. They've got no technology to work with, no tech to assimilate or pieces to use. They'd be starting from scratch, with a whole planet in front of them. At a certain point, they wouldn't even be able to "assimilate," they'd just have to straight-up "build."

Not only would it be not worth the investment (since the Borg famously only assimilate tech that will help them improve), but it would also be a HUGE pain. Imagine an assimilated Renaissance Earth: millions of Borg drones, but a planet of wood and stone. Anything before the late 20th century and they'd barely even have very much metal to re-forge. They would have to build mines just to extract the iron from the ground, so they could start building charging stations and ships.

Much better to assimilate the Federation as-is, with its huge population and powerful "modern" (for the future) infrastructure that can quickly be repurposed for the Borg's needs, and switch to time travel only when necessary.


There's no prize in assimilating Earth in the past.

Borg are driven to assimilate species only if they can add to the collective.

Humans are biologically inferior to species that the Borg have already assimilated.

The Borg are more interested in the Federation's technology.

Traveling back in time to assimilate pre-warp Earth would gain them nothing but a biologically unremarkable species with no redundant vital organs, etc.

What the Borg ought to do instead is send more than one ship to assimilate Earth.

We've heard about he Borg assimilating other Delta Quadrant species (like the one in VOY "Hope and Fear".) He spoke of 'hundreds of cubes' when the Borg finally got his species.

Both times the Borg launched an attack on Earth, it was just a single vessel that juuuuust about succeeded.

Sending two ships would be a better idea. Or three. Or fifteen.

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    As for "There's no prize in assimilating Earth in the past", then what was the point from all the First Contact movie?? Was it not to go back, send a signal to the Borg Collective at that time to know of earth and assimilate it? Commented Dec 31, 2012 at 0:18
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    There's no prize in assimilating Earth in the past. There is. The Federation has been the pain in the butt for the Borg for a decade or so, it did resist multiple tries to be destroyed and/or assimilated into the collective. Even Voyager, which is a single small ship far away from reinforcements, managed to outmaneuver being assimilated successfully multiple times and even deliver vital blows to the Borg. The Federation is what stands between the Borg and the Alpha-Quadrant, so it's logical to use all means necessary to get rid of them.
    – Bobby
    Commented Dec 31, 2012 at 12:11
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    @bobby True, but merely erasing the Federation is kind of the booby prize -- yes, it eliminates a major thorn in the Collective's side, but they don't actually gain anything in that scenario. Remember, the Borg grow by assimilating new species and perspectives and incorporating their strengths. The fact that the Federation is able to hold its own on multiple occasions is proof of just how much the Collective stands to gain from a victory. Commented May 13, 2013 at 14:25
  • The Borg see the humans as the driving force behind the Federation. All those that defied them the best have been human. Humans are devious beyond all other species they have met. Therefore, getting rid of humans, even in the past, will still get them some comfort. Besides which, they already have a good amount of Federation technology stored in that Borg sphere that went back in time. Transmit it to the collective from 400 years in the past and you're golden...
    – methuseus
    Commented May 13, 2014 at 16:49

Well, if we are to believe the later events in Voyager, then Borg ships needs transwarp conduits to travel very large distance at very high speeds. It is shown many times, so the Borg make significant technical progress (through assimilation) over the course of centuries. The transwarp network is a relatively recent addition, definitely less than three centuries old. So these transwarp conduits don't exist in the past, and traveling through time and then through space to get to past Earth is not an option.

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