There’s an even more fundamental reason why central planning can’t work - central planners simply cannot possess the information required to effectively allocate the nation’s resources. Not only because there’s far too much of it and the economy is far too complex, but because it doesn’t even exist until people are forced to make rational choices that central planning does not force them to make.
Pretend you are a central planner. You’re trying to figure out how many hammers to make this year for the construction industry. How do you do that? Well, you could ask all the people in the country if they need a hammer, and build them. But many people will say they do, and they really don’t. Hey, free hammer. But even if these people are honestly trying to help the state an only request a hammer they really need, they are still going to over-estimate. The information about the real need for hammers doesn’t exist until you weigh the personal value of owning a new hammer against the personal value of owning all the other things you could have instead. So even a person who could really use a hammer might actually rather have a new screwdriver, because he needs that even more - but no one asked him. He may not even realize he needs the screwdriver more, because the relationships between the things you value doesn’t even develop in you mind until you are forced to make trade-offs between them.
This is what prices do. They force you to rationally examine all your needs and decide which are more important. They tell you which jobs make more sense for you to do.
Then there’s the complexity aspect. You order more hammers. But now there’s a shortage of wood for the handles, because you didn’t tell the wood manufacturers to increase the harvest. Or maybe you did, but now there’s a shortage of logging vehicles. Or maybe you’re really smart and thought of that too. But now there’s a shortage of motor oil. Or a shortage of ball-bearings because the hammers you ordered increased demand for steel, which the ball-bearings in the trucks also need. The ramifications of any production decision in a complex economy are astounding. It’s kind of like the six-degrees of separation thing - a big order of hammers can wind up effecting the availability of corn flakes though a complex series of interactions no one person or central planning bureau can possibly understand.
Now think of the billions of decisions like this that are made every day. Imagine a central planner trying to sort out all the conflicting demands on the nation’s resources and allocate everything efficiently. It simply can’t be done. You can have the best, fastest, smartest computers in the world, and they can’t do it either, because the information they need to be efficient is still locked up in the brains of the citizenry.
A capitalist economy is like a massively networked, massively parallel computer system with billions of feedback loops keeping things in balance. Information flows through the price system, carrying the knowledge and desires of everyone exactly where it needs to go. If I decide I need a hammer, not only do I send a signal to the hammer manufacturer that his hammer is useful and in demand, but the fact that I didn’t buy other things sends signals to all the people I might have purchased from instead. Production is increased for hammers, and decreased for the other things. And hammer production raises demand for steel and wood, which raises their prices. This makes hammers slightly more expensive for the next person. But it also makes other things that use steel more expensive. So suddenly all the people who use steel have to decide if it’s still worth it. Some will switch to alternatives. Or their prices will go up and people will buy less, easing the demand on steel. Or maybe the increased price of hammers will decrease their demand, lowering the price of steel for the things we value more.
In the meantime, the new, higher price for steel stimulates production of it, reflecting the new reality of our increased desire for steel.
Everything falls back to an equilibrium, with new prices reflecting the new reality of the relative trade-offs of all these goods.
None of this can effectively happen in a centrally planned economy. That’s one reason why all centrally planned economies fail, and why they all tolerate a large black market - the black market becomes a market-driven safety valve which helps keep the whole rickety affair going for a while.
But the key question you asked is whether or not the Soviet Union could have survived. Sure it could have. Never underestimate the power of fear in keeping a crappy poor country going. North Korea is still around, despite its people being in a constant state of near-starvation. Saddam’s government was remarkably stable despite the horrible suffering of the people. Compared to those countries, life in the Soviet Union wasn’t that bad. North Korea has a per-capita income of a few hundred dollars a year. The Soviet Union had a per-capita income more than ten times higher. The people generally weren’t starving - they were just severely under-performing their potential.
It would have eventually collapsed, no doubt. But that collapse could have come in ten years, or in fifty.