With Ethereum (ETH 0.91%) rallying these days, maybe it's a good time to revisit the "flippening." The term (and it's as fun to say out loud as it is to read or write) is the moment that Ethereum bulls are waiting for. The flippening will take place the moment that the world's second-most-valuable cryptocurrency overtakes market leader Bitcoin (BTC 0.40%) in terms of market capitalization. 

There are no guarantees that the event will even happen, of course. Bitcoin continues to be the brand that every investor knows. The gap between the two digital currencies is also pretty substantial. Bitcoin, with its $434 billion price tag, is more than double Ethereum's market cap of $182 billion.

But with Ethereum now possibly weeks away from a historic milestone as it continues to be the blockchain platform of choice, it wouldn't surprise crypto traders if Bitcoin surrendered market leadership to its closest peer. Don't sleep on the flippening.

Someone seated at the table with various screens showing different charts.

Image source: Getty Images.

Trading places 

Momentum has been on Ethereum's side lately. It's up 37% over the past week as of Thursday morning, compared to a more modest but still potent 15% recovery for Bitcoin. Ethereum has also tripled Bitcoin's return over the past month. Stretch the timeline back a year (merrier times, for sure) and even Ethereum's 23% slide is marginally kinder than Bitcoin's 28% plunge.

It's naturally going to take a lot for Ethereum to flip the script. It would have to soar 139% from here. And Bitcoin would have to stand still. It's difficult to fathom because the market needs a reason to disconnect the two leading crypto denominations. When one rallies, the other is inching higher. When investor appetite cools, it tends to chill for both currencies. Bitcoin and Ethereum are both roughly 70% off the all-time highs they hit last year. 

If the flippening chatter isn't getting the same kind of traction it did a year or two ago, it's because both cryptos would need to triple from here to return to their peaks. The bullish case was that Ethereum would pass Bitcoin on the way up instead of being passing ships in a less inspiring market climate. 

Why is this baton-passing event even possible at this point? Ethereum bulls will point to the merge as the catalyst that could catapult their crypto of choice to the top. Bitcoin and Ethereum currently rely on proof-of-work models to generate new tokens. Mining for new Bitcoin or Ethereum relies on computation power, a validation process that is battle-tested and secure but a drain on energy resources. Proof of work is a red flag for critics with environmental concerns. 

Ethereum has spent the past two years working to shift to a proof-of-stake protocol. It's a consensus-based mechanism for validating new coins that is popular with many of the faster and more energy-efficient cryptocurrencies. Ethereum was initially hoping to complete the merge to proof of stake last year, but it has proved to be a herculean task. The can has been kicked through the first half of this year, and Ethereum programmers (for now) have Sept. 19 tentatively circled as the day for the migration to proof of stake to take place. 

Traders credit the new date for the surge in Ethereum over the past week, but we've seen deadlines come and go in the past. There are still concerns that this could be a "trade on the news" moment, especially if Ethereum keeps climbing ahead of the merge.

However, this could be the moment when Bitcoin and Ethereum truly separate from each other in terms of market sentiment and momentum. Bitcoin wears the market-cap crown right now because it planted the flag when it comes to crypto. It's the industry standard. Ethereum rose to second place by raising the bar with blockchain technology that powers smart contracts that fuel functionality beyond just a store of value or the means to settle up a transaction.

There are naturally many other types of cryptocurrencies out there, and they have their own particular strengths. A third digital currency could be the one that ultimately overtakes both Bitcoin and Ethereum to rise to the top.

Ethereum is the one we're watching now, though. It accounts for nearly two-thirds of the total value locked -- or deposited in decentralized finance protocol chains -- and many smaller digital currencies are there simply to make Ethereum more useful.

Time may be running out for the flippening to take place this year, but if the merge goes smoothly and Ethereum continues to distance itself from Bitcoin's current limitations, a shift in market sentiment could make it the top dog by 2023.