Not so sure, we are pulling resources out of the earth at a ridiculous rate. Even with green energy we are still reliant on mining for everything. Goods, fertilizer, the stuff for solar panels. We're going to run out of easy to access stuff sooner or later.

We could feed everyone now, but not sustainably. To produce the amount of food we do now, we need fertilizers made from limited resources like oil and pesticides/fungicides that destroy the ecosystem. If the current agriculture section of the world completely moved to sustainable practices next year there wouldn't be enough food to support half of the human population.

We can sustain everybody on Earth right now if we all eat beans and rice, give up all meat, stop plane travel, and limit your commutes to ones you can do without a personal car. Even if we get rid of billionaires, the rest of western life is unsustainable at this population.

If you are reading this message on a smart phone, it's already too late, you don't meet this criteria. The only solution for us to sustain your lifestyle is to reduce the population.

We CAN sustain everybody we have now.

Even if we could (which I doubt) is it even worth it living on a planet that’s this crowded?

Why that direction? Intuitively I'd imagine stuffing the humans into cities would allow more mass transit, fewer cars, more economies of scale, and more area left over for nature. So more like Singapore, less like Texas.

Has anyone ever done scientific research on this question?

Urban centers have less waste or CO2 per capita than their rural or suburban counterparts. The problem is our pursuit of ever increasing profits is extremely wasteful but is currently how states gain influence.

We produce enough food now, but not sustainably. Fertilizers and pesticides are destroying ecosystems.

We could also all sleep together in big rooms, like stadiums, to save heat and power elsewhere. And it won't turn into that orgy scene at the end of that Matrix movie, not unless Carol wants it to.

"In my perfect ideal world, that we have no path to achieving, we could sustain our large population indefinitely."

Hard to prove, but even the idea that the world can barely support the current population is likely just propaganda trying to reinforce a scarcity mindset.

We could probably pack nearly everyone in the entire world in to an area the size of the United Kingdom, and most could be living better lives than they do now. Population Density comparable to New York City would get you around 7 billion people. Obviously, we can do better than that, but just trying to put it into perspective.

Even for agriculture, you could support the current population with what we've got and a lot more if that was your priority. There are dramatic gains to be made by reducing or eliminating meat and unless we made some new unfortunate discoveries that would 100% get you there, but you might not even have to. We're strong into theory territory and might have to focus on prioritizing fertile land for agriculture but having everyone in the world eat like an average american would likely be doable at current levels if we actually wanted to prioritize that.

Kill* about 15 billionaires and suddenly we can support a lot more people with the same resources.

*Other options available