What happened

My, how time flies. Was it just two days ago that Virgin Galactic (SPCE 22.58%), Sir Richard Branson's pioneering space tourism company, was one of the hottest stocks on the market, gaining 23% on no news whatsoever?

And yet, by Thursday, at 1:45 p.m. EDT, Virgin Galactic stock is down 8.9% -- again on no news.

So what's up with that?

Virgin Galactic SpaceShipTwo rocketing away from the viewer

Image source: Virgin Galactic.

So what

"Excellent question. Next question, please."

Honestly, it's hard to say what's going through Virgin Galactic investors' minds today. On the newswires, there's no news specifically affecting Virgin Galactic today. Turn to Twitter, and it's pretty silent over there as well -- there's a video showing Virgin building one of its spaceships, but nothing really newsworthy.

Likewise, analysts have been silent on Virgin Galactic today. No upgrades, true, but no downgrades, either.

Now what

So why is Virgin Galactic stock falling today? I can't say for certain why, but I can't say that I'm surprised to see the stock in free fall, either.

The reason: Virgin Galactic today is much less a business, and much more a speculative stock that investors are gambling might turn into a business some day in the future. Despite its $3 billion market capitalization, Virgin Galactic earns no profit, and generates almost no revenue. (Its price-to-sales ratio is 795 right now.)

Because Virgin's valuation metrics are essentially meaningless, it's currently impossible for investors to determine if Virgin Galactic stock is underpriced, overpriced, or priced just right. Before we'll be able to determine that, the company will have to earn some profits that we can value it on.

To that end, it's worth pointing out that Virgin Galactic next reports quarterly earnings on May 5. Analysts expect it to lose $0.15 per share.