Why odd numbers are dodgy, evens are good, and 7 is everyone's favourite

The Japanese love odd numbers. When you give gifts you must always give three, five or seven items. Photograph: D. Hurst / Alamy/Alamy

Think of the number 7. Do you like it? Do you love it? Do you remain unmoved?

You may think these are frivolous questions, but when I launched an online survey asking people to submit their favourite numbers – and explain the reasons why – almost 4,000 people declared a devotion to 7.

"[It] cheers me up and gives me a feeling of comfort," said a female participant, aged 48, from Norway.

"[It] has great symbolic value as an expression of Muslim belief and the miracles of God," wrote a 25-year-old man in Lebanon.

"[It] is the best. Like a nice and clever woman," added a Hungarian man, aged 20.

Seven polled the highest in my global survey, making it – in my opinion – the world's favourite number, a result I revealed last week on myGuardian blog, and which was written up in news outlets across the world.

The survey, which attracted 44,000 participants, was self-selecting and therefore did not conform to the rigorous standards of a laboratory experiment. (Although I would wager than any professional poll would find the same results.) Yet academic studies that have investigated our emotional responses to numbers have found that they follow clear patterns.

Marisca Milikowski of the University of Amsterdam set up an experiment in which participants were shown all the numbers between 1 and 100 and asked to rank each number on a scale between good and bad, and between excitable and calm. Her results showed quite clearly that, in general, even numbers are seen as good, and odd numbers bad. Numbers ending 1, 2 or 3 are generally more excitable than the others, and even numbers are the most calm.

Dan King of the National University of Singapore and Chris Janiszewski of the University of Florida asked participants whether they liked, disliked or felt neutral about every number between 1 and 100, as the numbers appeared in random order on a screen. Data from this experiment showed that even numbers and ones ending in 5 are much better liked than the other odd numbers.

In other words, when asked to project non-mathematical meanings on to numbers, or to react emotionally to them, our responses are remarkably coherent. And these responses reflect numerical properties, most clearly size and divisibility by either 2 or 5.

It is interesting that our favourite number is 7, an odd number, when even numbers are more liked and seen as calmer and better than odd numbers. In fact, in my survey, favourite numbers are much more likely to be odd than even, with a ratio of 60/40. Counter-intuitively, our favourite numbers are generally not the ones we like best or rate as good. Like is very different from love.

We can explain the popularity of 7 as a favourite number by looking at a classic psychology experiment. When asked to think of a random number between 1 and 10, most people will think of 7. Our response is determined by arithmetic. The numbers 1 and 10 don't feel random enough, neither does 2, nor the other even numbers, nor 5, which is right in the middle … So we quickly eliminate all the numbers, leaving us with 7, since 7 is the only number that cannot be divided or multiplied within the first 10. Seven "feels" more random. It feels different from the others, more special, because – arithmetically speaking – it is.

Terence Hines of Pace University in the US conducted another experiment that helps explain why we view odd and even numbers differently. He displayed pairs of digits on a screen. These would be both odd, like 1 and 3; both even, like 6 and 8; or one of each, like 1 and 6. Participants were asked to press a button only when either both digits were even or both digits were odd. On average it took respondents 20% longer to press the button when both digits were odd. He calls it the "odd effect" – it takes our brains longer to process odd numbers. They are literally more thought-provoking.

When people explained their choices in my favourite number survey, their reasons were varied and surprisingly tender, such as 2 because the respondent has 2 piercings, 6 because the sixth track on the respondent's favourite albums is always the best, 17 for the number of minutes the respondent takes to cook rice, 24 because the respondent sleeps with her left leg kicked out like a 4 and her boyfriend sleeps like a 2 on his side, and 1,000,000,007 because it is the highest prime number he can remember.

"Having a favourite number means that you get a little buzz every time you happen to be sitting in seat 53 on a train, or notice that the time is 9.53," said one submission. "I can't think of a reason not to have a favourite number."

We learn at school that numbers are tools for counting, but our relationship with numbers is quite clearly a deep and complex one, dependent on many cultural and psychological factors.

In the far east, superstitions about numbers are more noticeable than in the west. For example, 4 is unlucky for speakers of Mandarin, Cantonese, Japanese and Korean because the word for "4" sounds the same as that for death. Brands avoid product lines with a 4 in them, hotels don't have fourth floors and aircraft don't have fourth rows. (This is more disruptive than western fear of 13, primarily since, being smaller, 4 occurs more often than 13).

Eight is a lucky number in east Asia, however, because it sounds like the word for prosperity. A study of newspaper adverts in China, Taiwan and Hong Kong showed that 8 is by far the most popular non-zero digit in a price (for example in ¥6,800, ¥280). If you put an 8 in your price you make the product seem much more alluring.

These superstitions are not lightly held. Indeed, the association of 4 with death has become a self-fulfilling prophecy. US health records show that, for Chinese and Japanese Americans, the chance of suffering a fatal heart attack is 7% higher on the 4th of the month than would be expected.

East Asians hold deep superstitions about numbers, yet outperform western nations in the international league tables of mathematical performance, which suggests that strong mystical beliefs about numbers are not an impediment to learning arithmetic skills.

In fact, I would argue that having any sort of belief about numbers encourages a playfulness and an intimacy with them, which ultimately makes you less scared of mathematics and better at sums. It pays to have a favourite number.

Alex Bellos's latest book is Alex Through The Looking-Glass, Bloomsbury, £18.99. To buy a copy for £15.19 with free UK p&p call 0330 333 6846 or visit guardianbookshop.co.uk. He tweets at@alexbellos

• This article was amended on Sunday 13 April 2014. We said originally that participants were asked to press a button only when both digits were odd. This should have read participants were asked to press a button only when either both digits were even or both digits were odd. This has been corrected.

THE ODD COUNTRY

■ The Japanese love odd numbers. When you give gifts, you must always give three five, or seven items.

■ When giving cash at a wedding, the preferred amounts are ¥30,000, ¥50,000 and ¥100,000. If, however, you don't want to pay more than ¥20,000, you have to "odd things out" by dividing that sum into one ¥10,000 and two ¥5,000 bills.

■ The obsession with odd numbers is so great in Japan, according to Professor Yutaka Nishiyama of the Osaka University of Economics, that when in 2000 the government released a ¥2,000 note, no one ever used it.

■ Odd numbers underlie more than just Japanese ideas about money. Inikebana, the traditional form of flower arranging, only odd numbers of stems are used, following the Buddhist belief that asymmetry reflects nature.

■ A restaurant serving kaiseki, a form of multi-course haute cuisine, serves always an odd number of dishes.

■ The annual children's celebration is called the Seven Five Three festival, in which only children who are aged seven, five and three can take part.

The remarkable self-organization of ants

To speed their foraging excursions, army ants build bridges with their own bodies, allowing others to race across a gap. Photograph: Alamy

Original story reprinted with permission from Quanta Magazine, an editorially independent division of SimonsFoundation.org, whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences.

Give a colony of garden ants a week and a pile of dirt, and they'll transform it into an underground edifice about the height of a skyscraper in an ant-scaled city. Without a blueprint or a leader, thousands of insectsmoving specks of dirt create a complex, spongelike structure with parallel levels connected by a network of tunnels. Some ant species even build living structures out of their bodies: army ants and fire ants in Central and South America assemble themselves into bridges that smooth their path on foraging expeditions, and certain types of fire ants cluster into makeshift rafts to escape floods.

How do insects with tiny brains engineer such impressive structures?

Scientists have been studying the social behavior of ants and other insects for decades, searching for chemical cues and other signals that the insects use to coordinate behavior. Much of this work has focused on understanding how ants decide where to forage or build their homes. But new research combining observations of ant behavior with modern imaging techniques and computational modeling is beginning to reveal the secrets of ant construction. It turns out that ants perform these complex tasks by obeying a few simple rules.

"People are finally starting to crack the problem of producing these structures, which are either made out of soil or the ants themselves," said Stephen Pratt, a biologist at Arizona State University. The organization of insect societies is a marquee example of a complex decentralized system that arises from the interactions of many individuals, he said.

Cracking these problems could lead to improvements in swarm robotics, large numbers of simple robots working together, as well as self-healing materials and other systems capable of organizing and fixing themselves. More broadly, identifying the rules that ants obey could help scientists understand how biologically complex systems emerge — for example, how groups of cells give rise to organs.

"Self-organizing mechanisms are present everywhere in nature, from the development of an embryo to the organization of large animal populations," said Simon Garnier, a biologist at the New Jersey Institute of Technology.

Guy Theraulaz, a behavioral biologist at the Research Center on Animal Cognition in Toulouse, France, and collaborators have been studying insect nests for the last 20 years, building more complex and realistic models as their data improved. They have discovered that three basic guidelines governing when and where ants pick up and drop off their building materials are sufficient to create sophisticated, multilayered structures.

"It all results from local interactions between the individuals," said Garnier, a former student of Theraulaz's who now studies living ant bridges. "The final structure emerges without central coordination."

Theraulaz's team painstakingly analyzed videos of ants crawling across petri dishes as they attempted to build a shelter, noting each time that an ant picked up or dropped off a grain of sand. The researchers discovered three main rules: The ants picked up grains at a constant rate, approximately 2 grains per minute; they preferred to drop them near other grains, forming a pillar; and they tended to choose grains previously handled by other ants, probably because of marking by a chemical pheromone.

The researchers used these three rules to build a computer model that mimicked the nest-building behavior. In the model, virtual ants moved randomly around a three dimensional space, picking up pieces of virtual sand soaked in a virtual pheromone. The model ants created pillars that looked just like those made by their biological counterparts. The researchers could alter the pillars' layout by changing how quickly the pheromone evaporates, which could explain why different environmental conditions, such as heat and humidity, influence the structure of ant nests. (They published a preliminary version of the model in a conference report in 2011 but haven't yet published the more refined version, which better mimics real ants.)

"The real novelty here is our newly acquired ability to observe in detail the formation and the transformations of these structures," Theraulaz said. "We finally have access to precise data on how living things get together to form complex yet fully functional and reactive structures."

After a weeklong simulation, the virtual ants created something that looked like a real nest; layers stacked together with connections between them. The connections themselves were not explicitly written into the rules, Theraulaz said.

"For the longest time, people never would have believed this is possible," said Chris Adami, a physicist and computational biologist at Michigan State University, who was not involved in the study. "When looking at complex animal behavior, people assumed they must be smart animals."

Cracking these problems could lead to improvements in swarm robotics. Photograph: Gert Brovad/Zoological Museum Co/PA

Living architecture

For David Hu and collaborators at the Georgia Institute of Technology, researching ant architecture is both a livelihood and a workplace headache. Hu's team studies living architecture in which "ants are the bricks and the brick layers," Hu said. But the fire ants in Hu's lab are also adroit escape artists. They build towers to escape their enclosures and creep under locked doors. Hu is terrified of three-day weekends, which give the ants more time to break free and build bivouacs — nests made of hundreds of thousands of ants — under his colleagues' desks. When everyone returns to work, he receives panicked calls from infested offices.

"We have ants escaping from our lab all the time," Hu said. "The bivouacs are sophisticated, with tunnels and windows that can open and close in response to humidity and temperature."

In his research, Hu is focused on first understanding a simpler structure — ant rafts. The insects can escape floods in their habitat by assembling into rafts made up of up to 100,000 members. The surprisingly buoyant structures, which can be as large as a dinner plate, can float for weeks, enabling the colony to survive and find a new home.

Hu and collaborators had previously shown that after a spoonful of ants is dropped into water, the blob of insects transforms into a pancakelike raft through a simple process: each ant walks randomly on the surface of the blob until it hits the water's edge. "An individual ant can't know how big the raft is, where it is in the raft and what other ants are doing," Hu said. "The only communication goes on at the edge of the structure — that's where the structure grows." Hu's team used these simple rules to build a virtual ant raft that had the same dynamics as one made by real ants.

Wanting to understand exactly what gives the ant rafts their remarkable strength and buoyancy, Hu's team peeked inside the structure. They froze rafts of ants and then created images of them using computed tomography (also known as CT scans).

The findings, which will be published in an upcoming paper in the Journal of Experimental Biology, reveal that ants weave themselves into something like three-dimensional Gore-Tex, a fabric that is both breathable and waterproof. The ants form air pockets by pushing away from whichever ants they are connected to, creating highly buoyant rafts that are 75% air. The weave of the ant fabric is held together by multiple connections among individual ants, which orient themselves perpendicular to one another. "What's happening at the big scale is the result of lots of interactions at the small scale," Hu said. The result is a water-repellant lattice that enables even the ants at the bottom of the structure to survive.

As an engineer, Hu views ant conglomerates like any other material, studying their properties much as one might study plastic, steel or honey. Ants, however, have the unusual ability to act as either a liquid or a solid, and Hu hopes further research into this ability will help engineers design self-healing structures such as bridges capable of sensing and mending cracks.

To find his ant architects, Garnier sometimes spends days with his collaborators wandering the rainforest on an island in the Panama Canal. But once in close range, the target is easy to spot: Huge swaths of army ants in search of food for their voracious young sometimes cover the length and almost half the width of a football field. Ants from this nomadic species, named for their characteristic marching columns, blanket their surroundings. To expedite their relentless foraging, the ants rapidly build bridges over gaps in their path or across trees, using their own bodies as building blocks to create a smooth and expedient path for their kin. Scientists have long studied these curious creatures, exploring the evolutionary advantages of their foraging and bridge-building tactics, but Garnier and collaborators are among the first to study exactly how the structures form. They build obstacles in the path of the marching column and record the ants as they build a bridge.

Like fire ant rafts, bridges are built based on simple rules and possess surprising strength and flexibility. As soon as an ant senses a gap in the road, it starts to build a bridge, which can reach a span of tens of centimeters and involve hundreds of ants. Once the structure is formed, the ants will maintain their position as long as they feel traffic overhead, dismantling the bridge as soon as the traffic lightens. "The exact timing of their decision to join or leave the structure maximizes stability as a function of traffic on the trail," Garnier said. "The rules of behavior in forming and dismantling the bridge are optimally designed to handle the traffic."

Garnier's team is now studying how individual ants cling to one another to create the structure and how ants at the fastening points can hold the weight of 100 comrades. "I think this is a new, very exciting approach," said Bert Hölldobler, an evolutionary biologist at Arizona State University who has been studying ants for more than 40 years.

One of the most exciting findings to emerge from studies of living architecture "is how dynamic and rich this process is," said Scott Turner, a biologist at the State University of New York College of Environmental Science and Forestry in Syracuse. Garnier's work shows that ants build and disassemble bridges according to changing needs. Preliminary work from Hu's group, which also studies bridges, shows that the structure's properties, such as strength and integrity, evolve with changing conditions.

Although Hölldobler is excited about all three projects, he cautions that just because a model mimics real ant behavior doesn't mean it reflects what's actually happening. He cites the case of a model of desert ants that re-created their complex foraging expeditions without the need for a chemical trail marker, created at a time when scientists had found no evidence for one. But Hölldobler's team later discovered that the insects do indeed use chemical markers, limiting the usefulness of the model.

Also currently missing is an evolutionary approach to understanding the ant behavior. "If we can understand how rules emerge from other rules and how they change with the environment, that would be extraordinarily fruitful," said Adami, who is planning to work with Garnier on this question.

Meanwhile, engineers are already dreaming up useful applications. They hope to use ant construction principles to design modular robots that can self-organize. Adami imagines a swarm of robots sent to Mars to build a structure from Martian soil ahead of the arrival of humans. The beauty of a decentralized system is that a project can succeed even if individual parts fail.

Dynamic ant architecture might also provide insight into how to make buildings more adaptive, changing its properties based on how many people are inside, for example. To make a living building, "you need to continually monitor the environment and what effect the swarm has on the environment," Turner said.

Ants might even shed light on the complex organization of the organ we use to study them — the brain. The behavior of an ant community resembles the organization of neurons into a functioning brain, Hölldobler said. "Each neuron is relatively dumb, but if you take billions of neurons, they interact in a way that we have only scratched the surface of understanding."

Original story reprinted with permission from Quanta Magazine, an editorially independent division of SimonsFoundation.org whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences

Particle Fever: the film that brings the Higgs boson to life

A natural: Monica Dunford, one of the Cern physicists who brings the search for the Higgs boson to life in Particle Fever.

A new documentary, Particle Fever, achieves the almost impossible: it makes the workings of the Large Hadron Collider comprehensible – and exciting – to even the most science-phobic viewer. Mark Levinson, the film's director, first visited Cern, home of the LHC on the Swiss-French border, in 2007 and kept going back until July 2012, when the crack team of physicists concluded a two-decade quest to find the Higgs boson.

Particle Fever follows half a dozen diverse characters – out of more than 10,000 scientists from more than 100 countries – who work on the world's largest and most expensive science experiment. It shows them theorising, arguing, playing table tennis. Levinson, 59, has been a sound editor since the 1980s – notably on many of Anthony Minghella's films – but he gained a PhD in particle physics before that.

You've said you don't think Particle Fever is a science documentary. What is it then?
I think it's about man's pursuit of understanding. I wanted to make a film that would appeal to people who may not even think they were interested in science but can relate to this absolutely amazing human endeavour. The Large Hadron Collider can be hard to justify in terms of expense – but, although it may not be needed for our survival, it is something that makes us human and important.

When you started filming, did you imagine that the Cern scientists would find the Higgs particle?
No. I definitely thought there would be the Higgs or something like it, but would they find it while we were filming? I did not think that. Almost all of the physicists said that the Higgs was so hard to find that it was probably going to take years of collecting data. In fact everybody thought that if they saw something it would maybe be a new particle, but not the Higgs.

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Physics appears to be a lot of staring at computer screens with numbers on them. How do you make that dramatic?
Luckily there was a lot of natural drama. We didn't have to invent it, we just had to recognise it and adapt to it as it happened. I've worked for a long time in the fiction world – I've written scripts, I directed a feature film before, but if I was scripting I don't think I could have actually done a better job in terms of creating the tension.

Are you referring to 2008, when the LHC closed down for more than a year because of a problem with the magnets? 
The accident was 10 days after I started shooting. My immediate reaction was: "Oh my God, there's my film!" But I realised they'd probably get it going again and that it was a great dramatic hook. There was a lot of pressure because of the accident, so it made the next startup even more tense, and then the result, which is really a cliffhanger about what's going to happen next.

How important was your own background in physics in making the film?
Oh, it was essential, I think. I was able to jump right in and I didn't have to do research into the physics that somebody who was just starting out would have to do. In some senses, physics hadn't changed much since I got out of it in the 80s, because they didn't have the LHC. So I knew what the situation was, I knew the people, I knew what their lives were like and I already knew what the stakes were.

At the heart of the film is the odd dynamic between theoretical and experimental physicists. Can you explain?
The stereotype is the solitary theorist sitting in a room by himself like Einstein and walking up to a board occasionally. They are very mathematical, abstract and, in some senses, the elite. But they need people to design experiments for them to give them feedback and point them in the right direction. The conflict often comes between their timescales. A theorist can wake up in the morning, suddenly erase an equation and rewrite it. An experimentalist, meanwhile, has been working on building a machine for 10 years to prove that theory.

You shot more than 500 hours of footage – how did the scientists feel about you following them around all that time? 
Many of them are film buffs and they loved the fact that I was a feature film-maker. They thought I was crazy shooting all this stuff but there was also the excitement that, who knows, maybe I'll introduce somebody to Nicole Kidman or something like that.

What's Cern like?
It feels very much like a university. There is probably more security than on many campuses, but once you get in, you can wander around – though there are certain places, like the underground cavern, you can't go. But most of the buildings are just open offices and then there's a first-class cafeteria with French chefs. That's a real hub, socially, but also a lot of people meet there and discuss physics while eating choucroute or fillets of fish. The French pastries are probably better than at any university I've ever been to and there's a big coffee culture.

Unusually, there's no narrator for the documentary. Why not?
We wanted it to feel like a drama, a character-based film, and if you have this omniscient narrator it just says "science documentary". So the idea was always to keep it more organic and weave it in so you almost don't realise you are being lectured in any way. It's more like personal tutoring.

Physicist-turned-film-maker: Mark Levinson, director of Particle Fever, has a PhD in the subject. Photograph: Daniel Zuchnik/WireImage

There are some fantastic communicators in the film – particularly a physicist called Monica Dunford. Did you have to interview hundreds to find the people you got?
I didn't interview hundreds. Monica was in the first dozen that I interviewed and I was lucky, because it was clear straight away that she had something special. Look, it's not only in science: the majority of people are not necessarily interesting, articulate and charismatic. I don't think these were totally exceptional, but I do think we happen to have some of the best.

Women have a prominent role in the film. Is that your experience of Cern or science in general?
No, and in fact I worried that we were maybe a little too woman-heavy because it was not representative. But we went with the best characters and I'm very happy it has ended up this way, because it's so clear that women are under-represented. You can see in the bigger shots in the control rooms, there's a number of women, but it's still maybe 30%, which is really low. It would be so satisfying if the film could have an impact on that.

Now is a boom time for popular science – do you plan to continue in that area?
I was spoiled in the subject here, but it has catalysed an interest in looking at science from a storytelling perspective. There's a book I'd like to adapt next – all I'll say is it has to do with molecular biology and music. Hopefully, there continues to be a hunger for these films.

An Imax screening of Particle Fever – with Mark Levinson and Monica Dunford in conversation with broadcaster and Guardian journalist Alok Jha – takes place at the Science Museum in London on 16 April (tickets available at sciencemuseum.org.uk)

Starwatch: Mars at its closest

Mars as seen from Earth in 1999 – the last time the two planets were similarly placed. Photograph: NASA/STScI

Mars comes closer to the Earth on 14 April than at any time since early 2008. Even so, it appears only 15.2 arcsec across through our telescopes and we need good observing conditions, and some patience, to appreciate its surface detail. Just don't expect as sharp a view as that in our Hubble image which dates from 1999, the last time that Mars and the Earth were similarly placed.

Mars was at opposition on 8 April when, by definition, it stood opposite the Sun in the sky so that it rose in the E as the sun set and was highest in the S in the middle of the night, about 01:00 BST. Mars, though, follows a relatively eccentric orbit and is now inbound from its farthest point so that its closest approach has been postponed by a few days. However, at 92.4 million km, it is only 450,000 km closer on the 14th than it was on the 8th.

There is no mistaking the distinctive glow of the Red Planet as it stands 5° above the full Moon on the evening of the 14th and shines at magnitude –1.4 to rival Sirius. Mars lies 9° NW of Virgo's main star Spica and is tracking westwards to pass 1.4° S of the famous binary star Porrima, or Gamma Virginis, on 3 May.

Overnight on the 14/15th, the Moon approaches Spica and begins to enter the fringe of the Earth's shadow as it sets at dawn for Britain. The resulting lunar eclipse is total for the Americas between 03:07 and 04:25 EDT, with at least some of the Moon's disc lying within the southern part of Earth's dark umbral shadow between 01:58 and 05:33 EDT.

Since Mars takes 687 days to orbit the Sun, the Earth overtakes it, and it comes to opposition, every 2 years and 7 weeks on average. That eccentric orbit, though, means that some oppositions are better than others. It may be closer than it has been since 2008, but in 2016 it is closer still and in 2018 it comes within 58 million km of us and its small globe, only 6,792 km across, swells to 24 arcsec. On the other hand, both these upcoming oppositions occur with Mars further S and lower in our sky. Indeed, in 2018 it is 2° further S in our summer night sky than is the Sun at midwinter – far from ideal for telescopic study.

The day on Mars is 40 minutes longer than on the Earth, so our view changes only a little if we observe at the same time from night to night. As in the Hubble image, the north polar cap is obvious as a white button, while other surface features process slowly across the disc as the planet turns. One of the more prominent, Syrtis Major, is the dark wedge that lies near the meridian on the image. This low-level shield volcano has darker rocks which are wind-swept relatively clear of the lighter-hued and rusty iron-rich sand and dust that blanket large areas of the surface. If we observe near midnight BST on the 22/23 April, then our view of Mars and of Syrtis Major should be almost identical to that in our image.

The north polar cap, mainly of water ice and tipped 22° towards us, was larger during the Martian winter when it had an additional dusting of frozen carbon dioxide. However, the summer solstice in Mars' northern hemisphere occurred two months ago, and much of the carbon dioxide has sublimed back into the atmosphere.

Nasa supplies to launch despite critical outage at International Space Station

Nasa astronaut Michael Hopkins during the previous attempt to repair the International Space Station. Photograph: Nasa/Reuters

Nasa is pressing ahead with Monday's planned launch of a supply ship despite a critical computer outage at the International Space Station, having determined that the situation is safe.

Mission managers decided on Sunday to proceed with the countdown for the SpaceX Dragon capsule, which is already a month late in delivering more than two tons of cargo. "We're good to go," said Nasa space station program manager Mike Suffredini.

Suffredini noted the many important supplies aboard the Dragon, including a new spacesuit and repair parts for the older spacesuits already in orbit. "We need to get it on board as soon as we practically can," he told reporters.

The backup computer, located on the outside of the space station, stopped working on Friday. The main computer kept operating perfectly, and the six-man crew was never in any danger. Nasa debated whether to delay the SpaceX mission and, on Sunday, determined the station has sufficient redundancy to safely support the visiting vessel.

A spacewalk will be required to replace the bad computer. Engineers don't know why it failed.

Suffredini said the spacewalk will be conducted by a pair of astronauts on 22 April, using suits outfitted with new fan components to avoid the near-disaster that occurred last summer. An Italian astronaut almost drowned when his helmet flooded with water from the suit's cooling system.

A 22 April spacewalk will give SpaceX two chances to get its unmanned Dragon capsule flying. Good weather is forecast for Monday's 4.58pm launch. If that doesn't work, the next launch attempt for the California company's Falcon rocket would come on Friday.

Nasa is paying SpaceX Space Exploration Technologies and Virginia-based Orbital Sciences to make station deliveries.

As soon as the Dragon soars, the space station's solar panels will be moved into the proper position for its arrival, Suffredini said. That will guard against any complications resulting from additional computer breakdowns.

More than a dozen of these computers, called MDMs or multiplexer-demultiplexers, are located on the exterior of the space station.

Fewer international science students come to 'unwelcoming' UK

Tough immigration rules are putting science students off the UK, says report. Photograph: Reuters

An "unwelcoming UK" has seen a drop in the number of international students studying science, technology, engineering and maths (Stem subjects), according to a House of Lords report.

The report says the policy on immigration has had a negative impact oninternational student enrolments on UK Stem courses, which have fallen by more than 10% in the past two years.

Produced by the House of Lords science and technology committee, the report urges the government to rethink its policy on immigration, and remove international students from net migration figures.

Complicated rules, a constantly shifting immigration policy, expensive visas and insufficient time to seek work after study all contribute to making the UK appear unwelcoming, the report finds.

Lord Krebs, chair of the science and technology committee, says: "When we really need to send the message that international Stem students will get a warm welcome in the UK, they're getting the cold shoulder and heading elsewhere."

Krebs says changes to the immigration rules have played a direct part in putting overseas students off the UK.

"The rules are seen as too complex and subject to endless changes, the visa costs are not competitive, and the rules relating to work after study are so limiting that prospective students are heading to the US, Australia, Canada and elsewhere," says Krebs.

The report offers some key recommendations for the Home Office, including removing students from migration targets, improving the way information is provided to prospective students to ensure "welcoming and clear language is used", a two-year government review of the package for international students to make sure it's globally competitive, and reinstating the post-study work visa – scrapped in 2012 – which the report claims was "simple and effective".

Krebs says: "Allowing just four months for a student to find work after graduation is more or less tantamount to telling overseas students they'd be better off going to study elsewhere."

This follows findings from a Higher Education Funding Council of England (Hefce) report showing a drop in the number of international students studying in UK universities for the first time in 29 years. The report also shows a 50% drop in the number of postgraduate students coming from India and Pakistan.

"This is further evidence that we are losing international students to other nations due to the UK's restrictive policy on post-study work visas," says Libby Hackett, chief executive of University Alliance.

Hackett adds: "This is harming our economy as well as our universities. There is a simple fix: reintroduce two-year post-study work visas for all graduates from trusted UK universities.

"Around 83% of international students are studying in the UK so that they can get a good job. We know that international students want to ensure that in addition to their time at university they will have the opportunity to undertake in-work placements and to contribute back to the UK."

Dr Jo Beall, director of education and society at the British Council, says: "Any drop in students must be investigated as the UK cannot afford a brain drain of the world's most ambitious young people.

"We support the committee's recommendation that calls for the re-classification of students in immigration data. For the UK to remain globally competitive, the focus must be on attracting and supporting international students."

A spokesperson from the Home Office says: "We do not accept that the UK's immigration rules are deterring international students and there is no clear evidence in the report to support that argument.

"The UK remains the second most popular destination for internationalhigher education students and our universities saw increases of new enrolments from key markets, including China (+6%), Malaysia (+3%) and Hong Kong (+18%) last year.

"The student visa system we inherited was weak and open to widespread abuse. We are controlling immigration while still attracting the brightest and the best."

Other countries have also experienced falling numbers of Indian students, with the US seeing a 6% drop and Australia a 40% drop over the past five years.

Despite the UK experiencing a drop in the number of international students studying Stem subjects, new figures show that overall numbers of students studying Stem in the UK is at an all-time high.

T rex skeleton embarks on cross-country road trip to Smithsonian

Pat Leiggi checks the contents of a crate containing fossilized bones from a Tyrannosaurus rex in Bozeman, Montana Photograph: Sepp Jannotta/AP

The rare and nearly intact skeleton of a Tyrannosaurus rex that roamed the earth 65 million years ago will set off from Montana on Friday on a cross-country road trip, its first, bound for the Smithsonian Institution in Washington DC.

The fossil of the 38-foot-long carnivore, found on federal lands in Montana in 1988, has played a starring role in scientific research at the Museum of the Rockies in Bozeman since its excavation by paleontologists led by curator Jack Horner.

The seven-ton skeleton of a dinosaur that may have been an opportunistic eater rather than a stone-cold killer is to be mounted at the Smithsonian Institution in an exhibit that will open in 2019 and is expected to attract 8 million visitors a year, Horner said. The dinosaur is on loan to the Smithsonian for 50 years.

The so-called Wankel T rex – named after Kathy Wankel who discovered it – was about 18-years-old when it died and is considered second for extensiveness and preservation only to Sue, the famed T rex at The Field Museum in Chicago, he said. Its gender is not known.

The loan of the T rex to the Smithsonian National Museum of Natural History is on par with the museum's 1929 acquisition of the priceless Hope diamond, said museum spokesman Randall Kremer. The Smithsonian until now has only displayed a cast of a T rex but not the real thing, he said.

Technology will speed the four-day road trip of the largest carnivorous dinosaur in the United States. Its hundreds of bones are packed in 16 crates installed in a 53-foot-long semi that hauler FedEx emblazoned with T rex images.

FedEx pledges to give the prehistoric creature "the first and best ride of his life" in a truck to be constantly monitored for such factors as barometric pressure, said spokeswoman Parul Bajaj.

Horner, adviser for the trio of Jurassic Park films, said his research suggests T rex was a scavenger tied to findings that it had bone-crushing teeth like animals that are not usually apex predators.

"But I'm glad they're gone. Otherwise, it would be a dangerous world. The only charming dinosaurs were the ones that didn't eat you," he said.

A send-off celebration at the Museum of the Rockies is to see hundreds of dinosaur fans escort the T rex through downtown Bozeman to the interstate.