Professor Michael Milford and his colleague Juxi Leitner assess the scientific plausibilities of Thor: Ragnarok and finds them difficult but not always impossible.

Thor: Ragnarok is the latest Marvel movie out today that sees Chris Hemsworth back as Thor, but he’s not on friendly home turf. Instead he finds himself imprisoned on the opposite side of the universe from his beloved Asgard, and out of his depth in a gladiatorial contest with the Incredible Hulk (Mark Ruffalo).

But Hulk isn’t his only problem. Ragnarok (the end of his homeland of Asgard) is looming and Thor has new villains to deal with, including the warlike Hela, played by Cate Blanchett.

Other new characters include the eccentric Grandmaster (Jeff Goldblum), the fallen warrior Valkyrie (Tessa Thompson), the conflicted Asgardian Skurge (Karl Urban) and the hilarious Korg (played in motion capture by the director Taika Waititi himself).

Given the light-hearted tone of the movie, we’re going to have some fun looking at the “science” of Thor: Ragnarok.

We’ll take it as a given that there are superheroes with magical capabilities, and look instead at the numbers behind some of the characters and events. As usual, there are some minor spoilers ahead.

How do Hulk’s pants stay on?

Hulk is infamous for his pants staying on through his transformations, both from Bruce Banner to Hulk and back again. Given that these are normal pants, is this possible?

First we can calculate how much they need to stretch. In the movie, Hulk is about 259cm (8ft 6ins) tall and very solidly built, as explained by VFX supervisor Jake Morrison. Banner, according to some sources, is about 178cm (5ft 10ins) tall, and actor Mark Ruffalo says he’s around 175cm. He has similar stature to me (Michael) and my waist measures about 40cm across at the front.

So in transitioning from Banner to Hulk, his height goes up by a factor of 1.46, while his waist circumference goes up by about 1.75 times – more than his height because in Hulk form he’s more bulky.

So his pants would need to stretch by about 75%.

Finding stretchiness factors for jeans is challenging. Fashion websites quote figures up to 4% for stretch jeans. A scientific study found “stretchability” of up to 34% (after a few washes). So conventional jeans are probably out.

Pure spandex pants, on the other hand, are viable – they can stretch by more than 100% and then return to their original size. So if Banner is willing to accept certain fashion choices, he can maintain decency while morphing both ways.

Verdict: It’s stretching science a bit, but plausible.

Calling Mjölnir

Thor’s hammer, also known as Mjölnir, has an unpleasant run-in with Hela in the movie. With some abuse of physics, we can examine how Thor might be able to call his hammer back at high speed.

If Thor is using and abusing normal physics, he might call the hammer back by playing with masses. The hammer looks to accelerate back to Thor faster than normal Earth gravity (9.81m/s²) would make it fall – so let’s say it accelerates back twice as fast – about 20m/s² – and he calls it back from 100 metres away.

There are at least two possibilities here: Thor increases his mass magically in a way that only affects the hammer, or the hammer increases its mass in a way that only interacts with a (magically unmoveable) Thor.

Either way, one of them has to temporarily have a much greater mass:

acceleration = gravitational constant × mass of large body / distance²

mass of large body = acceleration × distance² / gravitational constant

= ( 20 × 100² ) / ( 6.673 × 10^-11 )

= 3 × 10¹⁵kg (or 3,000,000,000,000,000kg)

This is quite close to the weight of the Mediterranean sea (but concentrated in one extremely dense superhero) – so there would definitely have to be some way for the increased mass to only gravitationally affect Thor and the hammer – otherwise the environment around them would get ripped to shreds as well.

Verdict: Real-world physics takes a bit of a hammering.

Thor versus Hulk: Who would win in a fight?

The movie addresses this controversial and much-debated question in one way. Fans have disagreed on it forever. They draw upon reference material from the comics and movies, and arguments around Thor being a deity and Hulk being capable of near-infinite strength based on his rage.

What we can look at is what sort of strength it would take for Thor to throw the much bigger Hulk around in a gladiatorial fight.

Hulk probably has a specific weight. We can calculate it by scaling up the weight of a bulky human bodybuilder to Hulk’s height. Weight will scale up with the cube law.

One of the biggest bodybuilders in the world right now is Mamdouh Elssbiay, who is 178cm tall and weighs in at about 144kg in the offseason. We can scale his weight up:

Hulk weight = bodybuilder weight × height ratio³

= 144 × (259 / 178)³

= 444kg

This weight is in the range that Marvel provides of 408-635kg for Hulk.

Thor seems to knock him straight through the air about 50 metres along a fairly flat trajectory, let’s say accelerating him up to a speed of 300km/h (83.33m/s).

Assuming perfect energy transfer (in reality there would be loss), Thor would have imparted the following energy to Hulk:

Hulk kinetic energy = 0.5 × mass × v²

= 0.5 × 444 × 83.33²

= 1,540,000 joules

The energy in a human punch depends on the sport, the intention of the punch, and the size and training level of the human, but it appears to be in the range of a few hundred joules.

So Thor’s punches would have to impart about 10,000 times more energy than a human punch to toss Hulk around like he does.

From a momentum perspective, for Thor to not shoot backwards when he punches Hulk, he would either have to temporarily have a great mass or have some other magical power that defies conservation of momentum laws.

Verdict: Lucky Thor’s a god.

Super superheroes or wretched Ragnarok?

Thor: Ragnarok is a fantastically funny movie, the best in the Thor series, and one that finally addresses some unanswered questions that comic fans have long debated.

The movie mixes elements that stay somewhat true to real-world physics (Hulk’s weight) and others that require blatant violations of them (Thor’s hammer; fighting).

Most importantly, we have calculated that it’s plausible for Hulk’s pants to stay on, maintaining decency through Banner to Hulk transitions and back again.

Michael Milford is a professor at Queensland University of Technology and Juxi Leitner is a research fellow in Robotics & AI at Queensland University of Technology

This article was originally published on The Conversation. Read the original article.

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The Spinoff’s science content is made possible thanks to the support of The MacDiarmid Institute for Advanced Materials and Nanotechnology, a national institute devoted to scientific research.

As New Zealanders rally our collective efforts in the pursuit of the ‘crazy and ambitious’ goal of a Predator Free New Zealand by 2050, we mustn’t lose our hearts, writes Nicola Toki.

In 2003, freshly minted with a Zoology degree, I began my first job with the Department of Conservation. It only took a couple of morning tea conversations with some experienced rangers in my local office to realise that my understanding of what conservation meant in New Zealand was rather limited. These wild and woolly folks were goat cullers, tahr shooters, stoat trappers and rat killers. They carried guns, spent days or weeks outside and devoted their time to trapping, baiting and shooting the introduced mammals that wreak havoc on our fragile and unique ecology. It was a rude awakening to realise that protecting New Zealand’s native wildlife often meant killing other species of animals in order to give the local flora and fauna a chance at survival.

Last month a tiny rural school in the North Island sparked international online outrage due to their planned annual “possum hunt” fundraising activity. Animal welfare groups in the United States put so much pressure on the school that they were forced to cancel it. The opponents to the hunt were appalled that New Zealand children were being encouraged to kill small furry animals as part of a school fund-raising opportunity. But in their vociferous opposition, all ecological context was lost.

Our wildlife is like nothing else on earth

New Zealand’s native wildlife is so unique, ancient and frankly bizarre that it has been described by author Jared Diamond as “the closest we will get to the opportunity to study life on another planet.”

In a country with no native land mammals other than two species of tiny bats, anything with four legs and fur and sharp gnashers has contributed to the steep decline and even extinction of many of our species that evolved over 80 million years in a ‘land without teeth’.

In the blink of time since humans and their furry friends set foot on Aotearoa’s shores, 50 species of birds have disappeared forever. Until very recently we had three species of native bats, but when a rat plague swept across South West Cape Island in the 1960s, the greater short-tailed bat was wiped off the planet. Fossil records show that tuatara were once found right across New Zealand, but they disappeared from the mainland after kiore arrived.

New Zealand’s poster child for threatened species conservation is the kākāpō, now restricted to a handful of predator-free offshore islands. What you may not know is that those big green nocturnal parrots were once as common as sparrows, and just 150 years ago explorer Charlie Douglas talked of “simply shaking the tree or bush till they tumbled on the ground, something like shaking down apples. I have seen as many as a half a dozen Kakapos knocked off one tutu bush this way.”

By 1991 there were only 51 kākāpō left, which we have only just managed to triple in the past 25 years.

The moment that the first kiore leaped off a waka and scuttled up the beach, and the kuri bounded into the bush, time started to run out for many of our most beloved species. Some 600 years later when our European ancestors made it to New Zealand, the onslaught of mammalian invaders they brought with them would prove to be a tide of teeth that might not have been turned back. Until now. With the Predator Free movement that has been building in momentum over the past five years, culminating in an announcement by the Prime Minister in 2016 that we would aspire to a ‘‘Predator Free New Zealand by 2050’, government agencies, businesses, communities, individuals and iwi have taken up the challenge to eradicate small furry animals with great gusto.

Bringing back the dawn chorus – the real reason for a Predator Free 2050

The bit that occasionally gets lost in this rallying cry is the reason we have taken up arms against those introduced mammals. We’re not doing it because we enjoy the thought of killing other creatures and that a body count is the target. We’re doing this out of necessity because these introduced mammals are killers that our ancient wildlife could never hope to keep up with, and because we simply do not have the benefit of time. In order to give our wildlife a chance to survive and thrive, it is necessary that we remove the threats.

For those of us who love animals, the New Zealand context of conservation can be a bitter pill to swallow. The myriad introduced animals that have made it to our shores did not choose to be here.

It is not the fault of stoats, rats or possums that they are here and doing such damage to our many precious native species. While we have very clear goals to remove them, and an urgent need to do so swiftly, we need to proceed with respect and understanding, and to make sure that we treat those animals in a way that is as humane, effective and justifiable as possible.

Stone cold killers?

I wrote recently of attending the launch of the Jane Goodall Institute in New Zealand. In our conversations, they’ve questioned the appropriateness of encouraging young people to trap and they have pointed out that children who are cruel to animals can grow up to be cruel to other people. There is some research to suggest that they are right.

I agree that we should not be encouraging our young people to be cruel to other living things. For families involved in pest control activities like trapping, context is king. Kiwi kids who want to do trapping (like these two Wellington girls) tend to have a good understanding of why they’re doing it and full credit to their parents and others for making that clear.

I also reckon that we should encourage our children to take a moment to think about the animal’s life that has just been taken. Many hunters and indigenous cultures pay respect to the animal they have dispatched, so why not spare a thought for the animals we find in our traps? I have changed my views on this over time. I once spoke of the need for “everyone to go out and snot some small furry animal” and now I think that was flippant and unkind. It’s not easy to kill another living thing, and nor should it be.

There has been criticism of the plethora of social media photos of grinning Kiwi faces dangling a dead rat by the tail, or thrusting a squashed stoat toward the camera. My take on the rise of ‘stoat selfies’ is that the grins aren’t about the death of a fellow animal, but the celebration of yet another important step in the journey to bringing back our native wildlife.

True kaitiakitanga and guardianship of our native wildlife is making sure that our birds, reptiles and invertebrates have a safe place to live. The key to getting it right is to hold onto empathy for other living things along the way.