The markets are starting the week in their trillion-dollar IPO era, now that SpaceX shares are trading.

Why it matters: Think of Musk's company like a pebble, a big one, thrown into a giant lake of equity — there will be ripples through the public and private markets, and they'll be rippling for a while.

• "Any large IPO has a gravitational pull to them, so they can have sizable effects on the public markets, on private markets and sectors," Aaron Mulvihill, a strategist at JPMorgan Asset Management, tells Axios.

State of play: Those impacts take time. SpaceX made only a small slice of its shares available to the market — around 5%.

• In a typical IPO, a company will offer up about 10%-20% of its shares as its float, Mulvihill says.
• This was done in part because of the company's high valuation — an IPO of 20% of a $2 trillion company might have been market-disrupting.

Between the lines: A float this small means that you should take all those big numbers about the company's valuation — and Musk's wealth, which Matt gets into below — with a dash of side-eye. It's all on paper for now.

• Kind of like if, say, the Girl Scouts made 1,000 boxes of Samoas cookies, but put only 50 boxes up for sale.
• People would bid up the price of those delicious caramel, chocolate and toasted coconut confections. But once more cookies hit the market, the price would likely fall. Or perhaps our willingness to spend big for these cookies forever keeps its price higher.
• "Hype often peaks on day one," Bill Smith, CEO of Renaissance Capital, wrote in a note yesterday.

By the numbers: The average IPO in this decade was down 26% from its offering price after one year, according to data from JPMorgan.

Zoom in: There's no question that investors are thirsty for SpaceX, particularly retail investors.

• SpaceX had the largest day of retail net buying for an IPO in recent history, per Vanda — $117.6 million in net buys, surpassing a record set by Coinbase in 2021.
• SpaceX accounted for roughly 56% of all retail net buying on Friday, per Vanda.

Zoom out: Retail wasn't alone on the buying spree. There are now 40 actively managed ETFs holding SpaceX in their portfolios, ETF analyst Eric Balchunas posted Saturday.

• This is a new thing. A lot of attention's been placed on whether the major indexes fast-tracked SpaceX because that would mean the biggest ETFs — the passive ones that track the Nasdaq, S&P 500, etc. — would be exposed to this new company pretty early.
• But these actively managed ETFs don't have rules to change. "They can buy, sell whenever, whatever pretty much," he says.

Friction point: You might hear that folks are upset about having SpaceX added to their investments, but clearly there are a lot of investors who are clamoring for it.

The big picture: The company is expected to gradually increase its float, as its lockup period expires and it gets listed on some major indexes.

• SpaceX is expected to list in the Nasdaq 100 index around July 6. That means all the ETFs and index funds that track the Nasdaq 100 — including the popular QQQ — will have to buy.
• It hits the Russell 1000 around September or December.

What to watch: Because the SpaceX IPO appears to have gone relatively smoothly, that clears the path for more mega IPOs — Anthropic and OpenAI likely among them this year.

• And if those AI behemoths have successful debuts, we could be looking at a very different stock market.

Musk's almost inconceivable fortune has expanded the Overton window of wealth.

Why it matters: Big, round numbers have a remarkable way of focusing minds and setting narratives.

• The first trillionaire — much less a trillionaire known for erratic personal behavior, online trolling and support for global right-wing politics — will likely reignite discussion of the diverging fortunes of wage earners and those with market-based wealth, as well as their growing political power.

Driving the news: Shares of Musk's space-launch, satellite services, AI and social media conglomerate SpaceX ended their first day of trading up 19.2%, to $160.95.

• At that price, Musk's publicly reported stake of roughly 6.4 billion shares of stock would be worth $1.03 trillion.
• Toss that on top of the market value of Musk's $340.141 billion worth of Tesla at Friday's close, and you find yourself at $1.37 trillion.

Context: This is an extreme case of a long-term trend in which those with market-based assets have seen their financial position supercharged, compared with wage-earning workers.

• The dynamic has been amplified by the surge in technology shares over the last few years.

Case in point: The gap has swelled between the wealth of the average California household and that of the richest 0.0002% of California households, as spotlighted in a recent paper from the University of California Berkeley economist Gabriel Zucman and his colleagues.

• The paper comes out in favor of California's proposed billionaires' tax, noting "the proposed one-off California billionaire tax of 5%, payable over five years, is both small relative to California billionaires' wealth gains and large relative to the taxes they currently pay. ... We find that an annual wealth tax on California billionaires could raise substantial additional revenue even after accounting for income tax losses due to mobility."

Yes, but: Musk decamped with his business empire to Texas a couple years back, which will deprive California tax officials of some benefits as of Friday's IPO. (In the past, IPO booms have created tax windfalls for the state.)

Flashback: Still, if history is any lesson, Musk's gobsmacking net worth could become a potent talking point for advocates of higher taxes on the rich, especially as the U.S. debt load seems increasingly burdensome and the finances of popular programs like Social Security worsen.

• In February, Bloomberg's Ben Steverman had a great yarn on how Standard Oil tycoon John D. Rockefeller's emergence as the world's first billionaire came amid a massive political backlash against concentrated wealth that ultimately gave birth to the income tax in 1913 and the estate tax a few years later.