In Harry Potter and the Cursed Child, why would anyone believe this rumor?

Question

From Harry Potter and the Cursed Child - Part I:

Scorpius Malfoy is talking with his best friend Albus Potter:

SCORPIUS: So your dad thinks the rumors are true -- I am the son of Voldemort?

ALBUS (nods): His department are currently investigating it.

SCORPIUS: Good. Let them. Sometimes -- sometimes I find myself thinking -- maybe they're true too.

ALBUS: No. They're not true. [...]

_{Harry Potter and the Cursed Child, Part I - Act Two, Scene Sixteen, Hogwarts Library - Page 143 - Scholastic}

Harry Potter and the Cursed Child picks up right at the point where Harry Potter and the Deathly Hallows leaves off, at the epilogue. It is nineteen years post-Hogwarts, and Scorpius Malfoy and Albus Potter are eleven-year-old first-years.

I'm about as good at math as J.K. Rowling (meaning I'm terrible at it!), so correct me if I'm wrong. Voldemort was killed at the Battle of Hogwarts in May of 1998. At least eight years post-Battle had to have passed before Albus and Scorpius were born (I'm estimating the boys were born in 2006). Voldemort would have had to have been alive in 2005/2006 in order to have ...

... fathered Scorpius Malfoy.

As the wizarding world was fully aware of Voldemort's death in 1998, why would anyone even remotely believe that Voldemort is ...

... Scorpius Malfoy's father?

I can understand the possibility of Harry believing the rumor because ...

... his scar hurt, and his scar is Harry's connection to Voldemort.

But other than Harry, it doesn't make sense to me why anyone would believe such a ridiculous rumor. So, why?

Answer 1

Time travel

SCORPIUS: The rumor is that my parents couldn’t have children. That my father and my grandfather were so desperate for a powerful heir, to prevent the end of the Malfoy line, that they . . . that they used a Time-Turner to send my mother back . . .

ALBUS: To send her back where?

ROSE: The rumor is that he’s Voldemort’s son, Albus.

—Harry Potter and the Cursed Child

In other words, Scorpius was not conceived after Voldemort's death; he was conceived before his death. Then, presumably, his mother traveled back to her present (eleven years prior to that scene, give or take) and gave birth to him. Or at least, that's how the rumor would have it.

Answer 2

The rumour is likely to have gotten started (and persisted) for the simple reason that most celebrity rumours get started; there's no solid evidence that the rumour is genuinely true, but it's true that it's a genuine rumour.

Rodolphus Lestrange told at least one person (his daughter) that Voldemort had fathered a love-child with the wife of one of his Death-eaters. It's conceivable that he was also telling others or maybe even heard the rumour from someone else.

It wouldn't have taken much for Voldemort's surviving followers to have been aware of this rumour swirling around his inner-circle of confidants and had begun to spread their own version of these rumours after realising that Draco hadn't fathered a child with his wife until after several years of marriage, suggesting that he might be impotent/infertile.

Answer 3

Two further points, one is mentioned by Draco himself:

Draco:

[...] Our child, Scorpius was born ... it was the best day of both our lives, although it weakened Astoria considerably. We hid ourselves away, the three of us. I wanted to conserve her strength ... and so the rumours started.

Harry:

I can't imagine what that was like.

Draco:

Astoria always knew that she was not destined for old age. She wanted me to have somebody when she left, because ... it is exceptionally lonely, being Draco Malfoy. I will always be suspected. There is no escaping the past. I never realised, though, that by hiding him away from this gossiping, judgemental world, I ensured that my son would emerge shrouded in worse suspicion than I ever endured.

Harry Potter and the Cursed Child - pp.278-9 - Little, Brown - Act Four, Scene Four)

It's a bit like the rumours about Ariana that Rita Skeeter rejuvenated in Deathly Hallows. You hide things away, people start to wonder, their imaginations run wild, and before you know it you've got a conspiracy theory that's weirder and worse than what you were trying to keep secret.

I don't wanna rub anyone up the wrong way, so I'll refrain from mentioning specifics, but there are some pretty wild conspiracies out there in the Muggle world, particularly if the government or the military is ever trying to keep anything under wraps.

The second point is fear. It's like the opposite of what Fudge and the Daily Prophet did in The Order of the Phoenix. People are terrified. They were terrified that Voldemort would come back after his attack on Harry. Then he did. Now he's gone, but is he really? It's too easy for people to convince themselves that he

had a child, who will return to carry on his legacy.

I don't know if you know cancer survivors, but my mum has a friend who survived breast cancer, and she's still not free of the fear it will return and sadly, she probably never will be.