Nasdaq nears 5,000—does a tech bubble loom?

"Yes we're in a bubble."

"Heck no, we're not in a bubble."

That was the conversation overheard at a recent tech meet in Shoreditch, London, where entrepreneurs and savvy tech investors debated over whether the Nasdaq trading within striking distance of 5,000 means bubbly, high-growth tech stocks were about to burst.

Read MoreNasdaq takes aim at 5,000

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The tech-heavy index has not trading above the 5,000 mark since March of 2000, about 15 years ago.

After hitting an all-time intraday high of 5,048 on March 10, 2000, stocks started to experience a dose a volatility, as investors questioned whether tech companies—which had been outperforming for quite some time—were worth the amount they were trading at.

What followed was a scary ride for many investors, including a massive crash in technology stocks—many of which are no longer around today.

Hedge funds and retail investors were left to watch their portfolio dwindle. Professionals who had their savings invested in tech stocks had to rethink whether now was the time to retire.

Since then, the Nasdaq has slowly, but surely, been on the up.

Read MoreWe're not in a tech bubble, but it's pretty hot: VC

2000 all over again?

Many stocks caught in (what is now known as) the dot-com crash of the early 2000s have recovered substantially.

Since lows hit in 2002, Monster Beverage has gained around 48,000 percent, Netflix is up over 15,000 percent and Apple is around 13,000 percent higher.

Given these staggering gains, as the Nasdaq approaches new highs, some investors are understandably concerned that the index may due a correction.

But there is less of a worry this time around, and here's why: valuations.

The old tech juggernauts that got crushed during the tech crash of 2000 – such as Yahoo, Microsoft and Cisco – have nowhere near the astronomic price-to-earnings ratios that they were trading at back then.

Take Oracle for example. Before the tech bubble burst, Oracle was trading at over 167 times earnings; fast forward to today, and it's 18 times earnings.

Super-sized valuations

Nasdaq to break 5000 this week?
Nasdaq to break 5000 this week?   

However, it's a slightly different story when looking at the private market.

Silicon Valley's hottest start-ups are commanding a lot of money from investors, despite a lack of understanding about how these companies plan to generate meaningful revenue.

Uber is valued at $41 billion, messaging app Snapchat raised its latest round with a $19 billion valuation and Pinterest? $11 billion. And the list doesn't stop there.

Read MoreInvesting in a tech bubble

So what's driving these super-sized valuations?

First, the rebound in the Nasdaq has fueled optimism around investing in tech. It has also got a boost from the success of tech initial public offerings (IPOs) from companies like Facebook and Alibaba.

Lastly: deal flow. Larger, more mature tech titans, like Google and Microsoft, are using mergers and acquisitions as a means to build out their pipeline and offer customers new technology.

While many start-ups may not justify their lofty valuations at this point, it's not stopping investors from knocking on their door. And it's this irrational thinking that has some people saying: yes, we are in a bubble.

Other experts disagree, but warn we are getting close.

"While I wouldn't say we have yet hit bubble status, it is certainly inspiring a lot of new money to enter the market and chase deals," noted Amish Jani, Managing Director of FirstMark Capital.