And no religions, too

Premise: All religions vanish today-No memories, history, churches, relics etc.
Do new religions develop? If so, what might they be like?
Might the world go atheist?

I expect new religions would spring up overnight. It’s human nature to want to have some understanding of life, some concept to explain a multitude of things. Even the knowledge we’ve built up through the centuries can’t explain everything, and as I’m sure you’ve observed a fair percentage of humans have less than thorough knowledge. Some folks just can’t wrap their head around atheism, so I think we’ll always have religions.

Could one get as big as any of the major ones that exist today, or would we have little pockets of conflicting religions here and there? Which would be more likely to develop-polytheism or monotheism?

New Religions would spring up overnight, especially in the undeveloped world. Too much mystery that needs to be explained somehow. But even in the developed world, people have a sense of “spiritualism” and believe in all sorts of kooky stuff around which religions would almost certainly be built.

But isn’t most spiritualism an offshoot of an already existing religion? I think religions would have to be established first before spiritualistic variations came forth.

I think it’s the other way around.

Not only would religions spring up overnight, it would be all of the same ones. In fact, they might even be strengthened.

Please explain to me how Christianity or Judaism could possibly spring up again without the religious history that caused them to exist in the first place?

I don’t think you’d get new religions right off. What you’d get would be superstitions, isolated irrational beliefs. It would take significantly longer for some people to come up with a whole new belief system, aka a religion. I doubt the new religions would resemble the old ones much, since they’d be coming out of an entirely different worldview and knowledge base. I also don’t think they’d be nearly as prevalent; people tend to buy into a religion when it’s taught to them young. There’d be some religious people yes, but probably not a majority.

I wouldn’t be surprised if instead we see a lot of people turning to religious-like belief systems that lack the supernatural component; faith based political philosophies like communism, conspiracy theories, etc. They seem to be better at converting adults than religion is.

Of course religions would return. No idea as to the form, but they would return.
All you need is for one person, call him crazy, call him spiritual, call him a prophet, to say that a higher power is speaking through him, and you’re well underway. Why would anyone believe the crazy person? Because the world is a scary and lonely place and it doesn’t always make a lot of sense.
Everyone, at one point or another asks the question “why am I here? What is the meaning of life?” Along comes someone with an answer. You are here because a Higher Power allows you to be. He loves you. He always loves you. And if you love him back He will take care of you after you die.
That makes sense doesn’t it? That’s comforting, isn’t it? Suddenly you’re not so alone and confused anymore. People want that and even if you got rid of all religion today, they would be craving something to fill that loss by tomorrow.

They would come about as a result of my misreading your OP.

Indeed, if all memory of them was erased, the world would start out as completely atheistic, but spirituality would soon form built around other myths.

Only if you’ve been fed the idea from early childhood.

EDIT: Note that in the closest we have to a real life version of this, the actual development of religion throughout history, humans started out believing in lots and lots of spirits and gods. Many of which were outright nasty. Not in one higher power, and not that the power in question was especially loving or helpful.

I would think that the information age we live in would hamper the isolationism that some religions depend on. Ask a question a thousand years ago, and you get your answer from the local wise man-ask it today and you get a vast variety of answers from people around the world, with evidence to compare.

Yes

Objectivism, N Korean Dear Leaderism, Scientology and the Raelians, I think - personality & sci-fi cults, basically.

It’s possible, but I don’t think it’s likely. Religion is such an easy tool to develop for controlling people, I expect it to be like flight - evolving multiple times, whenever there’s a niche for it to exploit.

The problem is that reasoning and critical thinking don’t just come into being in a vacuum. Without some kind of education in the scientific method, people would turn to easy explanations for the world around them . . . or whichever explanations they happen to come upon. All kinds of local religion would spring up overnight, and it wouldn’t take much for them to start fighting with each other for dominance.

Presumably you’re not looking for theistic answers, but from that point of view, obviously God can choose to reveal some or all of the same teachings again. Conversely, some believers, accepting the premise of your OP, might posit that the whole point of such a mind-wipe would be to introduce a wholly new covenant.

What do you mean by evidence, in this context?

For the purpose of this discussion let’s just assume what I propose can’t be undone or overruled by any deities.

That would depend on the question being asked, now wouldn’t it?

Dianetics will be a mainstrean religion in 500 years. That’s how they get started.

If all religions disappeared tomorrow and with them all the people who like to believe in them, then we’d have a chance of rebooting at least first world society without any religions.

But as long as we have billions of people who were raised with their innate desire to believe carefully fanned from birth by their parents & surrounding society, we’re stuck. And these people will continue to raise their kids that way, etc.
Consider the tendency to violence as an analog. You can raise humans to be pretty violent & vicious. Or you can raise them to be almost entirely non-violent. Violence is a human tendency which we can largely train out. And most human societies do that for most of their members. We’re still stuck with the bilogical tendency to violence in each new generation, but as long as society is dedicated to managing the problem it remains under societal control.

If the tendency to beleive in supernatural stuff & such was likewise viewed by society as an unfortunate human failing to be trained out wherever possible, and suppressed where not possible, we could get to a post-religious society over a couple generations.

But we’re not gonna get there overnight, nor will most of the present population worldwide be able to get there.

There would be new religions just as soon as the con artists dream them up.

Please re-read the OP. The premise is all religions gone, and all memories of said religions gone. With that premise in mind, what do you think would happen?

For example? With all the information now available at the speed it is available, please tell me what sort of religion could arise?