Physicists Just Came Up With a Mathematical Model for a Viable Time Machine

"Mathematically, it is possible."

BEC CREW

28 APR 2017

Physicists have come up with what they claim is a mathematical model of a theoretical "time machine" - a box that can move backwards and forwards through time and space.

The trick, they say, is to use the curvature of space-time in the Universe to bend time into a circle for hypothetical passengers sitting in the box, and that circle allows them to skip into the future and the past.

"People think of time travel as something as fiction. And we tend to think it's not possible because we don't actually do it," says theoretical physicist and mathematician, Ben Tippett, from the University of British Columbia in Canada.

"But, mathematically, it is possible."

Together with David Tsang, an astrophysicist at the University of Maryland, Tippett has used Einstein's theory of general relativity to come up with a mathematical model of what they're calling a Traversable Acausal Retrograde Domain in Space-time (yep, the acronym is literally TARDIS).

But before we get into the madness of legit time travel, let's put this into perspective real quick - the researchers aren't claiming to have a blueprint for a Doctor Who-style time machine that can be built tomorrow.

They say the materials we'd need to build this thing are so exotic, we haven't even discovered them yet... but we'll get to that in a minute.

Firstly, let's talk about what Tippett and Tsang are actually proposing. 

The model is based on the idea that instead of looking at the Universe in three spatial dimensions, with the fourth dimension (time) separated, we should be imagining those four dimensions simultaneously.

That allows us to consider the possibility of a space-time continuum, where different directions in space and time are all connected within the curved fabric of the Universe.

Einstein's theory of relativity links gravitational effects in the Universe to a curvature of space-time - the phenomenon thought to be behind the elliptical orbits of planets and stars.

If space-time were 'flat' or uncurved, planets would move in straight lines. But according to relativity, the geometry of space-time becomes curved in the vicinity of high-mass objects, which causes planets to bend their paths and rotate around their star instead.

What Tippett and Tsang argue is that it's not just physical space that can be bent and twisted in the Universe - time itself can also be curved in the vicinity of high-mass objects.

"The time direction of the space-time surface also shows curvature. There is evidence showing the closer to a black hole we get, time moves slower," says Tippett.

"My model of a time machine uses the curved space-time to bend time into a circle for the passengers, not in a straight line. That circle takes us back in time."

In order to harness this theoretical property, the physicists propose creating a kind of 'bubble' of space-time geometry, which carries whatever's inside it through space and time along a large circular path. 

If this bubble can hit speeds greater than the speed of light - something the pair say is mathematically possible - this would allow it to move backwards in time.

"It is a box which travels 'forwards' and then 'backwards' in time along a circular path through spacetime," the researchers explain in their paper.

"Delighted external observers would be able to watch the time travellers within the box evolving backwards in time: un-breaking eggs and separating cream from their coffee."

You can see the basic idea in the image below, with a passenger inside the bubble/time machine (person A), and an external observer standing beside it (person B). 

The arrow of time - which under normal circumstances (in our Universe, at least) always points forward, making the past become the present - is represented by the black arrows:

B. K. Tippett et. al.

Both person A and person B will experience time in dramatically different ways, the researchers explain:

"Within the bubble, A will see the B's events periodically evolve, and then reverse. Outside the bubble, observer B will see two versions of A emerge from the same location: one's clock hands will turn clockwise, the other counterclockwise."

In other words, the external observer would see two versions of the objects inside the time machine: one version evolving forwards in time, the other backwards.

While Tippett and Tsang say the maths is sound, the problem now is we don't actually have the right materials to build what they're proposing.

"While is it mathematically feasible, it is not yet possible to build a space-time machine because we need materials - which we call exotic matter - to bend space-time in these impossible ways, but they have yet to be discovered," says Tippett.

Their idea recalls another theoretical time machine - the Alcubierre drive, which would also use a shell of exotic matter to transport passengers through time and space (hypothetically).

Both ideas can't go very far without some idea of how to actually produce these space-time-bending materials, but as Tippett points out, we're never going to stop wondering about the possibilities of time travel, and this is just one more direction we can take this mind-bending physics.

"Studying space-time is both fascinating and problematic," he says.

"Experts in my field have been exploring the possibility of mathematical time machines since 1949, and my research presents a new method for doing it."

The research has been published in Classical and Quantum Gravity.

Physicists Discover an Unexpected Force Acting on Nanoparticles in a Vacuum ***

Physicists Discover an Unexpected Force Acting on Nanoparticles in a Vacuum

Nanoparticles can be pushed by pure nothingness.

FIONA MACDONALD

11 APR 2017

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Researchers have discovered a new and unexpected force that acts on nanoparticles in a vacuum, allowing them to be pushed around by pure 'nothingness'.

Of course, quantum physics is beginning to make it clear that 'nothingness', as we like to think of it, doesn't actually exist - even vacuums are filled with tiny electromagnetic fluctuations. This new research is further proof that we're only beginning to understand the strange forces that are at work at the smallest level of the material world, by showing how nothingness can drive lateral motion.

So how can a vacuum carry force? One of the first things we learn in classical physics is that in a perfect vacuum - a place entirely devoid of matter - friction can't exist, because empty space can't exert a force on objects travelling through it.

But, in recent years, quantum physicists have shown that vacuums are actually filled by tiny electromagnetic fluctuations that can interfere with the activity of photons - particles of light - and produce a measurable force on objects.

This is called the Casimir effect, and it was first predicted by physicists back in 1948. Now, the new study has shown that this effect is even more powerful than they imagined.

Why does that matter? This Casimir effect might only be measurable on the quantum scale, but as we start engineering smaller and smaller technology, it's becoming clear that these quantum effects can greatly influence the overall products.

"These studies are important because we are developing nanotechnologies where we're getting into distances and sizes that are so small that these types of forces can dominate everything else," said lead researcher Alejandro Manjavacas from the University of New Mexico in the US.

"We know these Casimir forces exist, so, what we're trying to do is figure out the overall impact they have [on] very small particles."

To figure out how else Casimir forces could impact nanoparticles, the team looked at what happened with nanoparticles rotating near a flat surface in a vacuum.

What they found was that the Casimir effect could actually push those nanoparticles laterally - even if they weren't touching the surface.

That's a little strange, but imagine it like this - you have a tiny sphere rotating over a surface that's constantly being bombarded with photons. While the photons slow down the rotation of the sphere, they also cause the sphere to move in a lateral direction.

University of New Mexico

In the classical physics world, friction would be needed between the sphere and the surface to achieve this lateral motion, but the quantum world doesn't follow the same results, and so it can be pushed across a surface even when it's not touching it.

"The nanoparticle experiences a lateral force as if it were in contact with the surface, even though is actually separated from it," said Manjavacas.

"It's a strange reaction but one that may prove to have significant impact for engineers."

All of this might sound a little obscure, but it could play an important role in figuring out how to develop smaller and smaller technology, as well as devices such as quantum computers.

Intriguingly, the researchers show that they could control the direction of the force by changing the distance between the particle and the surface, which could one day come in handy for engineers and researchers who are constantly looking for better ways to manipulate matter on the nano-scale.

The findings now need to be replicated and verified by other teams. But the fact that we now have evidence of an intriguing new force that could be used to direct nanoparticles within 'nothingness' is pretty exciting - and suggests we're one step closer to understanding the weird forces at work in the quantum world.

The research has been published in Physical Review Letters.

New Simulations Suggest Dark Energy Might Not Exist

68 percent of the Universe might not exist.

MIKE MCRAE

1APR 2017

Ever since the late 1990s, physicists have been fairly certain that the Universe isn't only getting bigger, it also appears to be expanding at an ever increasing rate.

A mysterious force called dark energy is currently thought to be responsible for this accelerating growth, but a new study raises the possibility that what seems to be a type of energy could be an illusion caused by the changing structure of the Universe.

Physicists from Loránd University in Hungary and the Institute for Astronomy at the University of Hawaii are now questioning if approximations in Einstein's equations introduced "serious side effects" that gave the illusion of a vast, unknown force pushing space apart.

If it exists, dark energy would make up about 68 percent of the energy in the observable Universe, but at just 10^-27 kilograms per square metre, it would be incredibly hard to spot in the laboratory.

In addition to the question of acceleration, dark energy also helps explain things like the overall shape of the Universe and the patterns of matter we see rippling through space.

The thing is, right now it's little more than an empty box without any other properties to describe the nature of its existence.

As such, it's currently assumed to be a fundamental part of empty space known as the cosmological constant, represented by the Greek letter lambda (Λ).  

Back in the early 20^th century, Einstein proposed the cosmological constant as a kind of fudge-factor to explain why all the mass scattered through the Universe wasn't pulling back together under the attraction of its own gravity.

When Edwin Hubble made it clear the Universe wasn't just resisting collapse, but actually expanding, the cosmological constant was thrown in the bin.

It's now known that the Universe appeared to grow at a slower rate in its youth than today, making the cosmological constant useful again as a way to explain this increase in speed.

Put together with another hypothetical 'black box' factor – dark matter, which would comprise of a further 27 percent of the known Universe – we get the Lambda Cold Dark Matter (ΛCDM) model to explain how the Universe evolved.

While Einstein's general theory of relativity was responsible for laying much of the groundwork for this model, the mathematics isn't always so easy to apply, prompting physicists to crunch parts of it down using educated assumptions.

But in this latest study, the researchers argue these approximations have ignored potentially significant influences of large scale structures within the Universe.

"Einstein's equations of general relativity that describe the expansion of the Universe are so complex mathematically that for a hundred years no solutions accounting for the effect of cosmic structures have been found," said László Dobos from Eötvös Loránd University.

If it were possible to step outside of the Universe for a moment and look down upon it, there'd be threads of galaxies called super clusters lining what look like relatively empty spaces.

The ΛCDM model assumes a uniform expansion that progressively gets faster thanks to the increasing push of dark energy overcoming the pull of dark and normal matter distributed evenly throughout space.

Yet according to the physicists involved in this new research, the large scale structures – 'bubbles' of seemingly empty space and the galaxies surrounding them – would create zones where expansion occurs at different rates, almost like mini-universes.

By mathematically modelling the effect of gravity on millions of particles representing dark matter, the team managed to recreate the bunching up of matter in the early Universe in such a way that it looked like the large scale galaxy structures.

While the Universe in their model still expands, the individual differences in how these bubbles expand averages out to an overall acceleration.

"Our findings rely on a mathematical conjecture which permits the differential expansion of space, consistent with general relativity, and they show how the formation of complex structures of matter affects the expansion," said Dobos.

"These issues were previously swept under the rug but taking them into account can explain the acceleration without the need for dark energy." 

The model makes its own necessary assumptions, but if it stands up to scrutiny it could explain why the Universe's expansion seems to be accelerating, all without the need for negative pressure.

While the idea itself is new, the search for ways to get around the need for a mysterious type of energy has produced a number of creative solutions in recent years.

Earlier this year, a study published in Science suggested dark energy could be explained as a kind of deficit, as if the Universe was 'leaking energy' at some point in its evolution.

While it breaks one of the big rules of physics (energy can't be lost or created) it would also take care of the nagging question mark over what 68 percent of the Universe is made out of.

There's no doubting dark energy is a tough nut to crack, so it might take thinking outside the box – if not outside the whole Universe – to find a solution.

This research was published in Monthly Notices of the Royal Astronomical Society.

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Physicists Have Detected a Friction-Like Force in a Perfect Vacuum

Without breaking the fundamental laws of physics.

BEC CREW

27 FEB 2017

One of the most fundamental tenets of modern physics is that in a perfect vacuum - a place entirely devoid of matter - no friction can possibly exist, because empty space cannot exert a force on objects travelling through it.

But despite the conventional wisdom, physicists in the UK discovered that a decaying atom travelling through a complete vacuum would experience a friction-like force, and now they've figured out how this reinforces - rather than breaks - Einstein's theory of general relativity.

"We spent ages searching for the mistake in the calculation and spent even more time exploring other strange effects until we found this (rather simple) solution," one of the team, Matthias Sonnleitner from the University of Glasgow told Lisa Zyga at Phys.org.

Sonnleitner and his colleagues were performing calculations to predict the behaviour of a decaying atom moving through a perfect vacuum when they noticed something strange.

For years, physicists have known that a perfect vacuum cannot exert any forces on an atom, but it can still interact with it.

It's impossible for physicists to physically create a perfect void, because no amount of decontamination can guarantee that a stray atom hasn't crept in, but calculations have predicted that a theoretically perfect vacuum would actually be buzzing with its own strange energy, filled with 'virtual' particle-antiparticle pairs that pop in and out of existence.

This 'empty but not empty' description of a perfect vacuum stems from an aspect of quantum mechanics called Heisenberg's uncertainty principle, which states that countless virtual particles could theoretically be appearing and disappearing at random moments in the void.

These quantum shifts produce randomly fluctuating electric fields, and the Glasgow team's calculations describe how they could interact with an atom travelling through a vacuum, causing it to absorb energy and enter an excited state.

As the excited atom decays to a lower energy state, it emits a photon (or light particle) in a random direction.

When the team calculated what happens when a photon is emitted while the atom is moving in the opposite direction to the photon, they detected a friction-like force that appeared to result in a loss of velocity.

If true, this would violate the principle of relativity, because it implies that 'observers' of the behaviour would see the atom moving at different speeds depending on where they were in relation to the atom.

Sonnleitner told Tim Wogan at Physics World that the team spent "weeks questioning their sanity" before figuring out the answer, and it all came down to E = mc².

They realised that as the moving atom decays to a lower energy state and emits a photon in a random direction, this causes it to lose a tiny amount of energy, which corresponds to a tiny amount of mass. 

This tiny amount of mass is known as the mass defect, and as Lisa Zyga reports for Phys.org, it's an amount so tiny, it has never been measured in this context before.

"This is the mass in Einstein's famous equation E = mc², which describes the amount of energy required to break up the nucleus of an atom into its protons and neutrons," says Zyga.

"This energy, called the 'internal binding energy', is regularly accounted for in nuclear physics, which deals with larger binding energies, but is typically considered negligible in the context of atom optics (the field here), because of the much lower energies."

When the researchers plugged this mass defect value into their calculations, using E = mc² to solve it, they found that by losing a tiny bit of mass as it decays, the atom actually loses momentum, not velocity.

If we look at the relationship between friction, velocity, and momentum, instead of seeing friction result from a change in momentum due to a loss of velocity, the scientists actually detected a loss of momentum due to a tiny change in its mass. Its velocity remains constant, as it should.

So instead of violating relativity by indicating friction in the vacuum, the phenomenon results in something that the principles of relativity actually predict - the decrease in mass causes the atom to lose a tiny amount of momentum, just as predicted by the conservation of energy and momentum in special relativity.

"[W]e have shown that, yes, a decaying atom sees a force resembling friction," the team concludes in their paper. "However, this force is a change in momentum due to a change in internal mass energy, and is not connected to decelerated motion."

The team says the next step will be to see if the phenomenon occurs when an atom absorbs - rather than emits - a photon.

And maybe someone will use it to help explain another study that hinted at friction in a perfect vacuum - in a 2011 study, physicists proposed that a vacuum could actually have friction if there are more of those 'virtual' particles pushing up against a spinning object than there are moving in the same direction.

The jury's still out on that, but one thing's for sure - strange things really do happen in the void.

The study has been published in Physical Review Letters.

پیشنهادی بر یک علم جدید: ریاضیات فیزیکی

یک علم جدید: ریاضیات فیزیکی (۰۷۳-۰۰۳)

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اسفند ۲۰, ۱۳۹۴
نویسنده: آقای "دی داد" پژوهشگر فلسفه و علم
ریاضیات, علمی, فلسفه ی علم, فلسفی, فیزیک

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ریاضیات و فیزیک دو شق از مهمترین شاخه های معرفت بشری هستند. شباهت ها و تفاوت های گوناگونی بین این دو حوزه قابل ذکر است.

از نگرگاه فلسفی مهمترین تفاوت همانا ذات این دو قسم از دانش است بنحویکه ریاضیات، تحلیلی و فیزیک، ترکیبی است. گزاره های ریاضیات احتمالا به عالم مُثُلِ افلاطون مربوطند اما گزاره های فیزیک به جهانِ عینی. در باب شباهت هم می توان از کمی بودن هر دو سخن به میان آورد. هدفی که من در این نوشتار دنبال خواهم کرد بحث تحویل این دو زمینه ی دانش به یکدیگر است.

می دانیم که می توان فیزیک را به ریاضیات تحویل کرد. کمتر پژوهشگری در تقدم ریاضیات بر فیزیک شک می کند. اگرچه رشته ای تحت عنوان فیزیک ریاضیاتی داریم اما حقیقتا نمی توان این زمینه را قدر مشترک این دو حوزه دانست زیرا من بر این باورم که در این حوزه از علم، نقش ریاضیات بیشتر از جنس یک ابزار است، نه چیزی بیشتر! البته در خودِ علم فیزیک نیز نقش ریاضیات “ابزاری” است اما خودِ علم فیزیک، ذاتی تجربی دارد در صورتیکه رشته ی فیزیکِ ریاضیاتی (Mathematical Physics) تا حد بیشتری انتزاعی است، همین.

من بر این باورم که قدر مشترک این دو حوزه علم جدیدی است که بیشتر می توان آن را از جنس ریاضیات دانست. یک مثال برای این قسم از علم، نظریه ی نسبیت عام است. من سابقا این شق جدید از علم را ریاضیات تجربی نامیده ام. حتی می توان از اسم ریاضیات فیزیکی نیز بهره جُست. در این نوع از علم، ما می توانیم به عالمی دست پیدا کنیم که تلفیق دو عالَم افلاطونی و عالم عینی است. کیفیت این جهان چیزی متفاوت اما در عین حال مشترک با هر دو این جهان هاست. طبیعتا گزاره های چنین علمی شق جدیدی از گزاره ها خواهند بود.

وقتی کریپکه می گوید که گزاره ی “H₂O آب است.” گزاره ای را نشان می دهد که دادن حکمی من باب تحلیلی و یا ترکیبی بودن آن به این سادگی ها محقق نمی گردد. از یک طرف این گزاره یک گزاره ی همانگویانه و یا بعبارتی تحلیلی است. از طرف دیگر رسیدن به این حکم که H₂O آب است، خود یک مسئله ی ترکیبی است. تفسیری که من روی این گزاره ارایه می دهم این است که موضوع گزاره یعنی H₂O، خود یک گزاره ی ترکیبی است. این گزاره ی ترکیبی در عالَم شیمی ساخته شده و سپس در یک ساختار منطقی قرار گرفته است.

البته می توان شق دیگری از آن را نیز متصور بود که در آن یک گزاره ی تحلیلی چونان موضوع یک گزاره ی ترکیبی قرار بگیرد. مثلا بگوئیم: “اینکه مثلث ۳ ضلع دارد بیان یک واقعیت بیرونی است.” در این مورد دوم، یک گزاره ی تحلیلی (مثلث ۳ ضلع دارد) چونان موضوع یک گزاره ی ترکیبی قرار گرفته و “واقعیت داشتن” چونان محمولِ آن گزاره ی ترکیبی بر موضوع آن حمل شده است. شق دوم شاید جذابیت کمتری برای دانش منطق و فلسفه داشته باشد ولی شق اول (وارد کردن یک گزاره ی ترکیبی به مثابه موضوع در یک گزاره ی تحلیلی) حقیقتا جذاب تر است.

جذابیت این نمونه از آنجایی نشات می گیرد که مسایلی ترکیبی در ساختارهایی تحلیلی بیان می شوند و آنگاه مشمول حکم های تماما صحیح و یا تماما غلط (مطلقات) خواهند شد. من این دست گزاره ها را برای سهولت بیشتر در نامیدن، گزاره های ترلیلی (یعنی ترکیبی در تحلیلی) و با معادل انگلیسی synlytical نامگذاری می کنم. این گزاره های دوجنسیتی به زعم من رقم زننده ی جنس گزاره های این شق جدید از علم خواهند بود. گزاره های این چنینی با موضوعات ترکیبی و حاصله از فیزیک شروع شده و به روابطی تحلیلی و حاصله از ریاضیات منتهی خواهند شد. بنظر من تمامی گزاره های نسبیت عام از جنس گزاره های ترکیبی در تحلیلی (سینلیتیکال) هستند.

نیروی جاذبه که در بدو امر بشکل تجربی و ترکیبی کشف و صورتبندی شده است، حال در یک نظام نظری محض و تحلیلی یعنی هندسه ی ریمانی (هندسه های نااقلیدسی و تجربی) توصیف می شود و تمامی این توصیفات همانا این همانی های ریاضیاتی هستند. جادوی این مسئله در این جا نهفته است. ما قادر خواهیم بود تا با دقت ریاضیاتی در رابطه با مسائل غیرریاضیاتی صحبت کنیم. گفتگو پیرامون مسائل ترکیبی (مثلا نیروهای کیهان) به این ترتیب فرصت بیان شدن در یک چارچوب یقینی را پیدا کرده و این چیزی است که ما بسیار برای نظریه ی همه چیز بدآن نیاز خواهیم داشت.

در این علم جدید (ریاضیات تجربی) ما قادر خواهیم بود ریسمان یا رشته ی فیزیکی تشکیل دهنده ی واقعیت کیهان را بعنوان موضوع در یک رابطه ی ریاضیاتی محض تحلیل کنیم و صفات آن را مورد مطالعه قرار دهیم، مثلا بگوئیم که طول آن چند واحد یقینیِ ریاضیاتی است و یا اینکه از چند نقطه ی تجربی (ذره ی بنیادین) تشکیل شده و چند عدد از آن ها می توانند در جهان وجود داشته باشد و غیره… در این ساحت است که ما با یک جهان توامان از-پیشی و از-پسی مواجه می شویم.

این نظریه جایگاهی است که در آن کارکردهای ذهن بشر قادر خواهند بود  بر مسایل ترکیبی حکم کرده و فارغ از مشاهده دست به پیش بینی بزنند. در این وادی است که می توان ریاضیات را به فیزیک تبدیل کرد. روابط حقیقی ریاضیاتی در این مقطع از جنس واقعیت فیزیکی جهان شده و با جهان مرتبط می شوند. تکرار می کنم، گزاره های نسبیت عام از چه جنسی هستند؟! همانطور که در بالا ذکر کردم، من آن ها را گزاره هایی ترلیلی می نامم.

یکی از مهمترین چالش های پیش رو علم در حال حاضر عدم پیوستن نیروی جاذبه به چارچوب کوانتومی است که در آن توانسته ایم ۳ نیروی دیگر کیهان را با هم متحد کنیم. علت نهفته در پس این عدم یکپارچه سازی را من نوعی ایراد فلسفی برمی شمارم. همانطور که می دانید کوانتوم از گزاره های ترکیبی و تئوری جاذبه ی نسبیتی از گزاره های ترلیلی استفاده می کند و یکی نبودن ذات این گزاره ها، هرگونه اتحادی را ناممکن می سازد.

گزاره های کوانتوم نیز می بایست ترلیلی گردند زیرا این شق از گزاره ها به حقیقت جهان نزدیک ترند. اگرچه نظریه ی مکانیک کوانتومی پیشرفته ترین و در عین حال مهمترین دستاورد علمی تاریخ است اما به گمان من، روش نسبیت عام، روش غایی است: توضیح جهان فیزیکی بتوسط جملات ریاضیاتی (نه فورمول های فیزیکی) که در آن ریاضیات صرفا یک ابزار محاسبه گر نیست. من نظریه ی نسبیت عام را اولین شاخه این علم جدید می دانم.

نظریه ی نسبیت عام با آن هندسه ی ریمانی اش که قادر است با ابزاری صرفا ریاضیاتی دست به پیش بینی در جهان عینی بزند، یک ریاضیات فیزیکی (Physical Mathematics) است. این ریاضیات تجربی با آن گزاره های ویژه، شرایطی را محقق می کند که علاوه بر یکپارچه شدن کل نظریات، بتوانیم به نظریه ای غایی برای همه چیز (tUToE) نایل آییم.

نظریه ی رشته ها (ریسمان) بعنوان ستون فقرات نظریه ی M، اگر ریاضیات تجربی دی دادی را اقتباس کند، قادر خواهد بود تا این وحدت بزرگ را در خلال کالبد خود تحقق بخشد. این علم جدید فضایی است که در آن تمامی نظریات تشکیل دهنده ی نظریه ی واحد به یک زبان (ترلیلی) صحبت کرده و قادر خواهند بود تا گفتمانی رویت پذیر را تحقق بخشند.