What does it mean that some scientists claim the universe was created from nothing. LoLL

0=1+(-1). That's what they meant.
Initially there was nothing( or zero) and from that zero, a positive came and to balance a negative energy too. We don't know what happened to negative energy(and negative matter with negative mass from negative energy), but we are in positive world.
Also the positive and negative, we use are arbitrary, so we may be negative!

When matter is created from energy you also get anti-matter and when the two come back together, they annihilate each other and you have energy. When energy is created, negative energy is created. It's like digging a hole to make a hill. M-theory has everything as vibrations of a membrane, the universe is just the pattern on the membrane from the collision of two membranes. For every wave, there is a trough. The ocean should be flat but it has waves. It's really more of a just because there's something doesn't mean it really isn't just nothing as it all averages out. Sort of a "What creation? I see no creation." answer to the theists. The interesting thing is, the more you think about it, the more right it is, there is no creation on the grander scale.

A quantum fluctuation event.

Although this will be very hard to understand, here it goes:
"Nothingness" actually has mass (albeit very little) and is rather unstable. Positive and negative energy fields have a net value of zero and can produce something literally from nothing. You may not like the answer, but it is consistent with the laws of physics and can actually be demonstrated in a lab. In fact quantum fluctuations are a key part in superconducters which we can create.

You would need a VERY advanced knowledge of math and physics to give you the details.

What does it mean if I say you have the potential to build a house? The house does not exist, but within you is the potential to build one, and indeed in a few months, we may literally see a house where a house did not exist.