Late at night rambling predictions...

No, they can only shoehorn "new information" back in dunno what year in universe (prior to ME3 ending), or you know, retcon.

If a story is set in the 18th century where everyone still uses sailing ships to get around the world, would you consider it credible that some guy magically finds the necessary information to build 20th century Apollo rockets?

Because that's how wide the gap in technology we're talking about here is.

Not a personal opinion, and certainly.

Modern, Citadel-based civlization has been around for 2700 years⁽¹⁾. During that time, they achieved an average speed of 4380 times the speed of light, or 12 light years a day⁽²⁾. By the time Shepard is commander of the Normandy, standard FTL drives can travel for 50 hours, or just over 2 days, before needing to discharge their drive cores⁽³⁾.

Now, at the speed of 12 light years a day, a standard vessel will take 23-41 years of FTL time (time when the FTL drive is on and consuming power) to cross the diameter of the Milky Way if they go in a straight line (including through the dangerous galactic core), and will have to discharge 4163-7500  times⁽⁴⁾ along the way. In the Milky Way galaxy, stars are on average 4 light years apart⁽⁵⁾, so a ship can reasonably expect to cross paths with at least two star systems in a day's cruise, assuming they are not travelling through the more sparse regions like the areas between the galactic arms.

Most, but not all, stars have planets. For obvious reasons, it's not safe to discharge in the vicinity of a star. So they have to avoid travelling through star systems without planets, and for maximum efficiency the planets they find should be gas giants so time and resources like food and power are not wasted as smaller planets take considerably longer to discharge into⁽⁶⁾. This presents some logistical issues that the game references when discussing Ilos from ME1 - a whole lot of scholars have long been looking to find Ilos for years, but expeditions to Ilos rarely goes beyond the planning stage because of the difficulties involved in exploring the galaxy without Mass Relays⁽⁷⁾. This gives us a sense of how difficult non-Relay travel in a galaxy really is.

Now, if that same ship wants to go to Andromeda through the void of intergalactic space, it has to bring along all the fuel, heat sinks, power and other resources it needs to last 570 years of FTL travel. That's easy, some people think, just make the Arks really huge so it has room for all the resources they need to bring along.

Well, the problem is that that extra ship mass and those extra resources increase the load on the eezo core, which has to work harder and drain more power to achieve the same mass reduction and speed. However, if you need more power to add more power storage, you're suddenly stuck with a recursion problem where the solution to your problem is part of the problem.

And that's not the only issue. The Mass Effect phenomenon, being a field of force like gravity and electromagnetism, obeys the inverse square law⁽⁸⁾, which states that the intensity of a physical quantity (in this case, mass reduction/increase) is inversely proportional to the distance of the effect. So a field twice as large would require four times as much energy to achieve the same intensity of mass reduction. In other words, a ship twice as big would require a field twice as big, and would therefore consume four times more energy to sustain the same level of mass reduction.

So upscaling the field from something the size of the Normandy to the Crucible-sized Arks and then having it function for 570 years straight, you're looking at some mindbogglingly, stupendously large amounts of energy. We're talking Alcubierre Drive, Jupiter's mass in energy-levels of energy. The only reason why this isn't a problem in the Milky Way is:

1) There are no ships as big as the Arks. Even the biggest ship in the galaxy, the Destiny's Ascension, is smaller than the smallest Reaper, whereas the Ark completely dwarfs the Reapers.
2) Because there are planets that can be accessed by automated drones to replenish vital resources, and discharged near.
3) Because of the Mass Relay network. Huge ships like dreadnoughts and carriers never stray far from system relays.

Can we get past this problem? Yes, the same way we transitioned from sailing ships to translunar rockets - by inventing far more efficient technology over the course of several decades or centuries. We're talking miniaturization on the scale of the total lifetime power output of a nuclear powerplant into storage the size of AA batteries.

I just don't see that kind of technological revolution happening in the three year span between ME1 and ME3. If Mass Effect: Andromeda was set 500 years into the future, I would have literally no problem with the plot as all the advanced technology can be explained away by the passing of time. I would still complain (this is my personal opinion, though) because it's a boring-ass setting, and it makes no sense going to a new galaxy when not even 1% of the Milky Way has been explored by the time ME3 occurs.

I hope you will find this answer satisfactory.

References:
(1) masseffect.wikia.com/wiki/Timeline#Council_Era_-_Formation_.28500_BCE_-_1_CE.29
(2) masseffect.wikia.com/wiki/FTL#Physics
(3) masseffect.wikia.com/wiki/Codex/Ships_and_Vehicles#FTL_Drive:_Drive_Charge, first paragraph
(4) The galaxy is between 100,000-180,000 light years wide according to recent evidence.
(5) cse.ssl.berkeley.edu/chips_epo/EducationBrief/CHIPS-Educational_Brief.htm
(6) masseffect.wikia.com/wiki/Codex/Ships_and_Vehicles#FTL_Drive:_Drive_Charge, last paragraph
(7) masseffect.wikia.com/wiki/Ilos#Codex_Entry
(8) hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html


Yeah but prothean beacons and million year old weapon blueprints is in a whole different ballpark than spacecraft technology far more advanced than what the Reapers have.

Thanks for the detailed reply.  A bit more effort into that than I was expecting.

You make some very good points.

To be honest, before reading a few more threads, I'd assumed that what was shown in the trailer was some big local alien ship or station, not the ark.  So if Bioware goes down the route of getting to Andromeda on it's own power via FTL, I'd pictured something more like the Saturn V principle.  ie.a big ass engine and a ridiculous amount of fuel with a relatively small payload (maybe similar size or smaller than the Destiny Ascension).

If that thing really is the ark, I'd have to agree the shear size looks like a problem.  And really, whatever means of propulsion, I hope they come up with a decent explanation for that thing.

Aside for a couple of minor points not worth quibbling over, the only thing I'd possibly argue with is that you claim traveling to the nearest galaxy is more advanced than Reaper technology. 

- Milky Way is Approximately 100 000 light years across.
- Distance to Andromeda is approximately 2.5 million light years. 
- We know the Reapers were chilling in Dark Space, but do we know how far out?
- I believe the idea is that after the Citadel link was shut down, they cruised into the Galaxy under their own power, which took a couple of years.

The distance to Andromeda is further than that traveled by the Reapers over the course of ME2, but not ridiculously off-the-scale further.  At least it doesn't have to be (depends how far out you think they were, really).  I don't think it's necessary to say Reapers couldn't have made the journey if they had wanted to, or even that they didn't.  I don't think that particularly breaks the game lore. 

However, I think the best option would be a re-purposed Mass Relay.  We know the Prothians were on the brink of figuring out Mass Relay technology.  It wouldn't be such a big stretch that someone could have found their work on Ilos and figured out how to point one at Andromeda (maybe destroying the relay in the process).  How are these things powered anyway?  Do they ever need refueling?

In general though, I like the basic premise of fleeing the Milky Way on account of it's seemingly imminent destruction.  It's a nice weighty starting point for the game, regardless of whether you've played the original.  Even if it does conveniently dispose of the problem of the *a-hem* 3 choices.

For me that's probably more important than being too slavish to the lore, as long as they do their best not to completely steam roller it.

But, yeah.  That Ark ship.  Hmmmm.

Well yeah.

It's always hard to square story lore with real life numbers. Something I indulged in as well, too be honest.

We're already playing a game that relies heavily on space fairy dust (element zero), so I'm inclined to be lenient about these things unless explicitly ruled out by previous games.

Eezo isn't consumed during FTL, it just interacts with electricity to generate mass effect fields. Negative current reduces mass, positive current increases mass. The only thing that is consumed in the process is electricity (although eezo will decay over time and become unusable).

Also, the Tantalus core cost 120 BILLION credits, not million.

No, the goal is to make more money without bruising Mac's sensitive ego. If the goal was REALLY to get away from the ME3 endings, they would just have retconned them out of existence and replaced them with a generic but comparatively acceptable "The Reapers were defeated, the end"-ending, like I've proposed a million trillion times.

Retconning the galaxy's technological level to enable intergalactic travel just creates more problems than it solves. For example, if such technology existed, why wasn't it used to great effect against the Reapers? Why wasn't it used by archeologists to find Ilos long before Shepard did? If they can send a giant-ass Ark 2.5 million light years without refuelling, discharging or restocking on power, why the fuck does ANY of their ships need to refuel, discharge or restock on power?

Just because BioWare ignores those questions doesn't mean they just magically disappear. 

I take by Oooooozo, you actually mean Eezo? If that's the case, then I think that we'll be searching for it harder than ever. Imagine traveling 300 miles in your car, at the end of the trip... You'll be looking for a gas station.