WMG / A Quiet Place

Per wiki policy, Spoilers Off applies here and all spoilers are unmarked. You Have Been Warned.

The baby is a replacement child

Think about it.

• Exhibit #1: The opening scene. The family gathers medications and likely has plenty of other paths to other stores, suggesting that birth control and condoms would be available. Given the risks of having a baby, we can reasonably assume that any pregnancy is on purpose.
• Exhibit #2: The timeline. The little boy dies on Day 89, and the time skip jumps to the 470s. A pregnancy is nine months or roughly 270 days. This means that the conception took place roughly around Day 200. 111 days is enough time for a couple to grieve over the loss of their child, make the decision to have another, and conceive.
• Exhibit #3: The baby being a boy. The new child being a boy just like the dead one wouldn't have been that much of a coincidence, but what really piqued my curiosity was that the mother specifically mentioned the baby being a boy and only this. This is really the only detail of the baby she mentions to the father. Granted, I know the "baby gender" is a big deal for everyone in real life and fiction but the exclusion of all other details (i.e. something like "He has your eyes") suggests the baby being male has a meaning that goes beyond just the standard general reveal.
• Exhibit #4: The risks and effort against the lack of any other clear driving motive. Why else would the parents take such risks? Having a baby in the world of A Quiet Place is practically suicidal, and the preparations to keep one safe are clearly very extensive. A soundproof crib in a semi-soundproofed room is not something you rig up in an afternoon. Only extraordinary dedication and willpower would make one even consider it, and what better one than to fill a hole left by a previous death? Yes, I know mourning and loss doesn't work that way in real life, but it's certainly plausible as a character motivation, and definitely better than some vague duty to preserve the human race. In addition, the practical benefits of having another child (i.e. more manpower for the farm) don't seem worth it: the family seems just fine with only four members (none of them are ill or starving, and they have nice-looking meals and enough free time to play board games and manufacture cochlear implants) and if they needed another helping hand so badly they'd have perished long before the child grew old enough to not be a burden.
• Exhibit #5: The obsession over finding the weaknesses of the monsters. Usually when characters in an apocalyptic scenario want to find a weakness or cure or whatever, it's because they either want to fight back and reclaim the world (i.e. clearing the streets of zombies) or because of some ticking-clock element (a rapidly-spreading disease or a steadily-progressing alien invasion). However, the family in A Quiet Place don't have any such ambitions or obligations. There is no race against time to find a cure before they're infected or figure out a way around the alien forcefields before they kill everyone. The film makes it clear that these people have stable lives, extremely tense but relatively safe and content, with only one rule needed to stay alive: stay quiet, except when your noise can be obscured by a larger source. It's worth noting that the only new, destabilizing element in their lives is the baby, which per Exhibit #1 and #4 we can assume was intentional. How does this factor into wanting to kill the aliens? Simple: as a pre-emptive measure to prevent their next child from being killed. The family is already well-versed in how to survive and can more or less co-exist with the aliens indefinitely, but a new member would be likely to make mistakes and thus expose themselves and everyone else to danger. If a weakness could be found then they could be hunted down and dispatched before the baby was even born. We already saw that they had a whole fireworks show set up just so the wife could have labor. It's not a stretch to say that the quest to find out how to kill the aliens was yet another measure.

The unseen creature is the Midnight Entity.

The way it makes knocking sounds on the roof in the teaser trailer is enough proof of its existence. The next thing the entity would do is possess one of the family members and repeat them.

• Very unlikely. The movie is set in 2025, in the Doctor Who universe. An alien invasion of this magnitude would have been shown in an episode set in the near future (Day of the Moon for example). The creatures here are blind. It wasn't the case for the Midnight Entity. The creatures here kill and show no signs of being able to possess a human (or a Time Lord). The living conditions on Midnight and on Earth are very different, it seems really unlikely that something living on Midnight can survive on Earth without a hazmat suit.
  • The movie is set in 2021. The memorial cross confirms that Day 89 was sometime in 2020, so Days 472 and 473 must take place in 2021.

The film is set After the End.

Something bad happened to the world, the family is one of the last (or maybe the last) on Earth. The monster, whatever it is, is from the species that now dominates the world.

• Looks to be confirmed by the Super Bowl teaser, which implies the monster is part of an invading alien force that conquered the Earth.

The entire family is dead by the end.

The family has no apparent way to escape the house without making noise and thus attracting the monster, so this could happen if they try.

• The end result: Sort of. The father and youngest son are both dead, and while the family now knows how to beat the aliens, making such loud noise will keep attracting more of them.
  • The weakness of the aliens wasn't the sounds, it was the frequency.

It's an experiment.

The family was abducted by a government or a secret agency. It's just a test to see how long an average family can survive without making noise. Of course they didn't volunteer and the only way to get out is to die. The purpose of this experiment? Well, the government/agency found a monster that reacts to sound, it would be a shame not to see what he is able to do.

• Jossed. It's an alien invasion.
  • ...or IS it?
  • Pretty handily jossed in the sequel. In the Just Before the End Flashback, you see the asteroid the creatures came from crashing to Earth.

The film is part of the Cloverfield franchise.

At least one theory posits this to be the case (seen here), and it's not totally unlikely, especially since John Krasinski was reportedly up for a role in The Cloverfield Paradox before scheduling conflicts with Jack Ryan forced him out.

• Jossed by Word of God. It has no connection to Cloverfield, although there were plans to make it set in that series at one time.

The film is part of the Predator franchise.

The unseen creature is a Predator.

• I am sorry if I am being a jerk but that makes zero sense. The predators hunt by slight, not sound, and in almost every depiction of them, showed them as to being able to see in infrared at the very least along side other vision types due to their masks. The predators are shown to be the type of hunters that only look for prey that can fight back and even in Predators where we are dealing with a rogue group of predators who don't care about tradition, they are shown kidnapping warriors and killers for their game reserve, not defenseless humans. There is no reason a predator would go after a family, and even if the father was a badass ex-spec ops that still does not mean a predator would kill the rest of his family. The fact that it is implied the creature kills a child further dismisses the creature being a predator. The child had a toy, not a weapon, so if the creature was a predator, it would have no reason to go after it, and in fact predator culture would demand he ignore the child. It is also implied that the creature is not invisible, but rather just too fast for a regular camera to capture, which is not something that is shown to be something a predator is capable of. Finally, the predators view hunting as a rite of passage and as such would not fully invade earth and lose out on a hunting ground, nor has any sources to my knowledge show predators doing large scale invasions of planets like what is shown in the trailer. Even the predators from Predators did not invade earth, and they are the rogue splinter faction.

The unseen creature is a giant vesp.

The film's premise (family with deaf daughter tries to survive in a depopulated world full of sound-seeking deadly creatures) is virtually identical to that of Tim Lebbon's 2016 novel The Silence.

The creatures are blind

They hunt by sound or even a form of echolocation, hence why it’s so crucial not to make any sounds.

• Confirmed. The creatures are attracted only by sound.

The creatures are an evolved form of Hollowgasts.

They're eyeless, have long claws on their front limbs and hunt by sound. Plus they are also huge.

The Creatures are Future Predators

What bits of them seen resemble the 'Primeval'' creatures, and they are sound based hunters.

The creatures are wild life from a significantly darker and inhospitable planet. They rode a meteor to Earth

Some of this was already mentioned via Word of God. Basically, in order to survive on their home planet, they needed to survive in darkness, with flying objects which can hit as hard as armor piercing ammunition, meteors, etc. Also, its kind of implied they can survive nukes since its almost certain at least one military gave it a try after it was clear things were turning into a Curb-Stomp Battle.

The creatures are just the first wave of the invasion.

The creatures don't appear intelligent enough to use spacecraft, but are actually biological weapons designed to cause as much death and chaos as possible before the real invasion begins.

• Jossed, as co-writer John Krasinski has said that the creatures evolved to be the apex predator on their home planet with no light, and their impenetrable armour enabled them to survive in space when their planet was destroyed.

The creatures don't eat what they kill because they aren't hungry, but because the noises have a negative effect on them.

They are incredibly sensitive to sounds, so whenever they hear noise it sends them into an angry frenzy. They want to destroy things that make sound because it annoys them, not because they are hunting to eat.

The creatures are primitive forms of Arachnids and this is near the start of the war.

The creatures are an advanced scout/invasion for the Arachnids and a rather successful one given the state of humanity in the start of the film. Once knowledge of the creatures' weakness spreads through the world a global effort to fight back against the invaders takes decades and maybe even centuries, during which both sides escalate and evolve towards the state of things in Starship Troopers.