As the longest ever U.S. bull market continues, investors are looking for stocks that will continue to outperform — but pure speculation is pushing some stocks inexplicably higher in the past few weeks.

But this phenomenon is not new, as it is characteristic of a "late cycle" market, explained Peter Boockvar, chief investment officer at Bleakley Advisory Group.

"In the history of the stock market there are always names that pop up and are the poster boys for speculation — companies that could cure cancer, take us to the Moon or Mars," Boockvar told CNBC. "For the broader market it's reflective of risk appetite and people willing to roll the dice."

Tesla, Virgin Galactic and even hydrogen engine maker Plug Power have all seen astronomical gains since the beginning of the year, with each of the stocks essentially doubling or even tripling. Each of the stocks fall firmly in the speculative category, with investors valuing the companies on what it could earn in the future – not what it does now. Most of the big moves are happening without any major news.

"In a world right now where there is slowing growth, there is a search on for anything growth related ... and what's cooler than electric vehicles and space?" Boockvar said.