A team of scientists at the Weizmann Institute have successfully created an 'embryo model' that closely resembles a 14-day-old human embryo, without using sperm, eggs or womb.
It is certainly not a simulation, and although it apparently started with different components they manipulated those to behave the way the normal versions do.
What would happen if they implanted it in a womb?
For one thing human embryos would have already been implanted in a womb for a week at that point and a great deal of signaling occurs between embryo and the uterus.
I read somewhere that pregnancy (unlike what is normally described) is a tug of war between the embryo which is the leach if you will on the mother which is the host. The embryo basically try consumes the host and so long as everybody is doing what they're supposed to, all the mechanisms end up keeping that war at bay with both participants making it alive at the end. If some mechanisms (and signals) were to misbehave one of the two would cease to exist.
At what point? Implantation typically occurs 6-12 days after fertilization. This experiment starts at the equivalent of day 7. IVF is a thing.
It sounds like you're just guessing.
Edited to add, this article says "It would be illegal to implant them into a patient’s womb" which is a far cry from what you are implying, that it would be impossible.
https://www.theguardian.com/science/2023/jun/14/synthetic-hu...
“This stage corresponds to day 7 of the natural human embryo, around the time it implants itself in the womb.”
“The researchers discovered that if the embryo is not enveloped by placenta-forming cells in the right manner at day 3 of the protocol (corresponding to day 10 in natural embryonic development), its internal structures, such as the yolk sac, fail to properly develop.”
“The stem cell–based embryo-like structures (termed SEMs) developed normally outside the womb for 8 days, reaching a developmental stage equivalent to day 14 in human embryonic development.” (So ~1 week post implantation for a human embryo.)
This research in animals has led to successful implantation, but not live births. Nobody knows why yet.
People could be up in arms if hypothetically 50% of these where viable, but the nonviable 50% would still cause errors when compared to human embryos. Alternatively, 100% could be viable and they could still be different in critical ways from natural human embryos resulting in universally late or premature births etc. Or perhaps 0% are viable and people just don’t understand the nuances.
It’s therefore an orthogonal question.
The discrepancy exists because people can track the day of ovulation and hormonal changes from implantation but actual fertilization has no obvious signs, unless your doing IVF or something and looking at the actual egg.
That said, extreme outliers may exist but that’s not what we’re talking about.
Here's an example of how IVF embryos are graded at day 6, prior to implantation:
https://flo.health/getting-pregnant/trouble-conceiving/ferti...
I think you missed the fact that these models start at the equivalent of day 7, so we're right in the same time window of implantation. Unless you are claiming that exactly at 6 days after fertilization is when every single embryo implants, and at 7 days it is simply too late. But your whole point seems to be that the window is hard to observe, so I doubt that's what you mean.
At any rate, I still see nothing to indicate that these "models" are not simply embryos. I think they are intentionally calling them models so that they can skirt the legal requirements about embryo research.
Unless of course you can point me to something that is actually different about one of these models vs an embryo. The whole article is about how they are the same.