Hexbyte  News  Computers Rotating Black Holes May Serve as Gentle Portals for Hyperspace Travel | JSTOR Daily

Hexbyte News Computers Rotating Black Holes May Serve as Gentle Portals for Hyperspace Travel | JSTOR Daily

Hexbyte News Computers

One of the most cherished science fiction scenarios is using a black hole as a portal to another dimension or time or universe. That fantasy may be closer to reality than previously imagined.

Black holes are perhaps the most mysterious objects in the universe. They are the consequence of gravity crushing a dying star without limit, leading to the formation of a true singularity – which happens when an entire star gets compressed down to a single point yielding an object with infinite density. This dense and hot singularity punches a hole in the fabric of spacetime itself, possibly opening up an opportunity for hyperspace travel. That is, a short cut through spacetime allowing for travel over cosmic scale distances in a short period.

Researchers previously thought that any spacecraft attempting to use a black hole as a portal of this type would have to reckon with nature at its worst. The hot and dense singularity would cause the spacecraft to endure a sequence of increasingly uncomfortable tidal stretching and squeezing before being completely vaporized.

Flying through a Black Hole

My team at the University of Massachusetts Dartmouth and a colleague at Georgia Gwinnett College have shown that all black holes are not created equal. If the black hole like Sagittarius A*, located at the center of our own galaxy, is large and rotating, then the outlook for a spacecraft changes dramatically. That’s because the singularity that a spacecraft would have to contend with is very gentle and could allow for a very peaceful passage.

The reason that this is possible is that the relevant singularity inside a rotating black hole is technically “weak,” and thus does not damage objects that interact with it. At first, this fact may seem counter intuitive. But one can think of it as analogous to the common experience of quickly passing one’s finger through a candle’s near 2,000-degree flame, without getting burned.

Hold your finger close to the flame and it will burn. Swipe it through quickly and you won’t feel much. Similarly, passing through a large rotating black hole, you are more likely to come out the other side unharmed.mirbasar/Shutterstock.com

My colleague Lior Burko and I have been investigating the physics of black holes for over two decades. In 2016, my Ph.D. student, Caroline Mallary, inspired by Christopher Nolan’s blockbuster film “Interstellar,” set out to test if Cooper (Matthew McConaughey’s character), could survive his fall deep into Gargantua – a fictional, supermassive, rapidly rotating black hole some 100 million times the mass of our sun. “Interstellar” was based on a book written by Nobel Prize-winning astrophysicist Kip Thorne and Gargantua’s physical properties are central to the plot of this Hollywood movie.

Building on work done by physicist Amos Ori two decades prior, and armed with her strong computational skills, Mallary built a computer model that would capture most of the essential physical effects on a spacecraft, or any large object, falling into a large, rotating black hole like Sagittarius A*.

Not Even a Bumpy Ride?

What she discovered is that under all conditions an object falling into a rotating black hole would not experience infinitely large effects upon passage through the hole’s so-called inner horizon singularity. This is the singularity that an object entering a rotating black hole cannot maneuver around or avoid. Not only that, under the right circumstances, these effects may be negligibly small, allowing for a rather comfortable passage through the singularity. In fact, there may no noticeable effects on the falling object at all. This increases the feasibility of using large, rotating black holes as portals for hyperspace travel.

Mallary also discovered a feature that was not fully appreciated before: the fact that the effects of the singularity in the context of a rotating black hole would result in rapidly increasing cycles of stretching and squeezing on the spacecraft. But for very large black holes like Gargantua, the strength of this effect would be very small. So, the spacecraft and any individuals on board would not detect it.

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This graph depicts the physical strain on the spacecraft’s steel frame as it plummets into a rotating black hole. The inset shows a detailed zoom-in for very late times. The important thing to note is that the strain increases dramatically close to the black hole, but does not grow indefinitely. Therefore, the spacecraft and its inhabitants may survive the journey.Khanna/UMassD

The crucial point is that these effects do not increase without bound; in fact, they stay finite, even though the stresses on the spacecraft tend to grow indefinitely as it approaches the black hole.

There are a few important simplifying assumptions and resulting caveats in the context of Mallary’s model. The main assumption is that the black hole under consideration is completely isolated and thus not subject to constant disturbances by a source such as another star in its vicinity or even any falling radiation. While this assumption allows important simplifications, it is worth noting that most black holes are surrounded by cosmic material – dust, gas, radiation.

Therefore, a natural extension of Mallary’s work would be to perform a similar study in the context of a more realistic astrophysical black hole.

Mallary’s approach of using a computer simulation to examine the effects of a black hole on an object is very common in the field of black hole physics. Needless to say, we do not have the capability of performing real experiments in or near black holes yet, so scientists resort to theory and simulations to develop an understanding, by making predictions and new discoveries.


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This article is republished from The Conversation under a Creative Commons license. Read the original article.

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By: Sethanne Howard

Journal of the Washington Academy of Sciences, Vol. 97, No. 2 (Summer 2011), pp. 1-28

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Hexbyte  Hacker News  Computers Viewpoint: Black Hole Evolution Traced Out with Loop Quantum Gravity

Hexbyte Hacker News Computers Viewpoint: Black Hole Evolution Traced Out with Loop Quantum Gravity

Hexbyte Hacker News Computers

  • Carlo Rovelli, Center of Theoretical Physics, CNRS, Aix-Marseille University and Toulon University, Marseille, France

Physics 11, 127

Loop quantum gravity—a theory that extends general relativity by quantizing spacetime—predicts that black holes evolve into white holes.

Hexbyte  Hacker News  Computers Figure captionHexbyte  Hacker News  Computers expand figure

F. Vidotto/University of the Basque Country

Figure 1: Artist rendering of the black-to-white-hole transition. Using loop quantum gravity, Ashtekar, Olmedo, and Singh predict that black holes evolve into white holes.

Black holes are remarkable entities. On the one hand, they have now become familiar astrophysical objects that have been observed in large numbers and in many ways: we have evidence of stellar-mass holes dancing around with a companion star, of gigantic holes at the center of galaxies pulling in spiraling disks of matter, and of black hole pairs merging in a spray of gravitational waves. All of this is beautifully accounted for by Einstein’s century-old theory of general relativity. Yet, on the other hand, black holes remain highly mysterious. We see matter falling into them, but we are in the dark about what happens to this matter when it reaches the center of the hole.

Abhay Ashtekar and Javier Olmedo at Pennsylvania State University in University Park and Parampreet Singh at Louisiana State University, Baton Rouge, have taken a step toward answering this question [1]. They have shown that loop quantum gravity—a candidate theory for providing a quantum-mechanical description of gravity—predicts that spacetime continues across the center of the hole into a new region that exists in the future and has the geometry of the interior of a white hole. A white hole is the time-reversed image of a black hole: in it, matter can only move outwards. The passage “across the center” into a future region is counterintuitive; it is possible thanks to the strong distortion of the spacetime geometry inside the hole that is allowed by general relativity. This result supports a hypothesis under investigation by numerous research groups: the future of all black holes may be to convert into a real white hole, from which the matter that has fallen inside can bounce out. However, existing theories have not been able to fully show a way for this bounce to happen. That loop quantum gravity manages to do it is an indication that this theory has ripened enough to tackle real-world situations.

The reason why we are in the dark about aspects of black hole physics is that quantum phenomena dominate at the center and in the future of these objects. Classical general relativity predicts that a black hole lives forever and that its center is a “singularity” where space and time end. These predictions are not realistic because they disregard quantum effects. To tackle these effects we need a quantum theory of gravity. We don’t yet have consensus on such a theory, but we have candidates, some of which are now reaching the point of allowing actual calculations on the quantum behavior of black holes. Loop quantum gravity, which has a clean conceptual structure and a well-defined mathematical formulation based on representing the fabric of space as a spin network that evolves in time, is one such theory.

During the last few years, a number of research groups have applied loop theory to explore the evolution of black holes. These efforts are building a compelling picture based on a black-to-white-hole transition scenario (Fig. 1), which can be summarized as follows [2]. At the center of the black hole, space and time do not end in a singularity, but continue across a short transition region where the Einstein equations are violated by quantum effects. From this region, space and time emerge with the structure of a white hole interior, a possibility suggested in the 1930s by physicist John Lighton Synge [3]. As the hole’s center evolves, its external surface, or “horizon,” slowly shrinks because of the emission of radiation—a phenomenon first described by Stephen Hawking. This shrinkage continues until the horizon reaches the Planck size (the characteristic scale of quantum gravity) or earlier [4, 5], at which point a quantum transition (“quantum tunneling”) happens at the horizon, turning it into the horizon of a white hole (Fig. 2). Thanks to the peculiar distorted relativistic geometry, the white hole interior born at the center joins the white horizon, completing the formation of the white hole.

Hexbyte  Hacker News  Computers Figure captionHexbyte  Hacker News  Computers expand figure
Figure 2: Diagram representing the spacetime evolution of a black hole into a white hole via a quantum transition. The vertical axis represents time; the horizontal axis represents distance from the center.

Loosely speaking, the full phenomenon is analogous to the bouncing of a ball. A ball falls to the ground, bounces, and then moves up. The upward motion after the bounce is the time-reversed version of the falling ball. Similarly, a black hole “bounces” and emerges as its time-reversed version—a white hole. Collapsing matter does not disappear at the center: it bounces up through the white hole. Energy and information that fell into the black hole emerge from the white hole. The configuration where the compression is maximal, which separates the black hole from the white hole, is called a “Planck star.” Because of the huge time distortion allowed by relativity, the time for the process to happen can be short (microseconds) when measured from inside the hole but long (billions of years) when measured from the outside. Black holes might be bouncing stars seen in extreme slow motion.

This is a compelling picture because it removes the singularity at a black hole’s center and resolves the paradox of the apparent disappearance of energy and information into a black hole. Until now, this black-to-white-hole picture was not derived from an actual quantum theory of gravity; it was just conjectured—and implemented with ad hoc modifications to Einstein’s general relativity equations. Ashtekar, Olmedo, and Singh have shown that a crucial ingredient of this scenario, the transition at the center, follows from a genuine quantum gravity theory, namely, loop theory. The result was obtained through an approximation of the full loop-quantum-gravity equations [6]—similar to the one employed in previous work aimed at resolving the big bang singularity [7].

It is important to note that the Ashtekar-Olmedo-Singh model addresses only the transition at the center of the hole. To complete the picture, we also need the calculation of the tunneling at the horizon [5]. Preliminary steps in this direction have been taken, but the problem is open. Its solution would lead to a complete understanding of the quantum physics of black holes.

It is not implausible that empirical observations could support this scenario. Models suggest that several observed astrophysical phenomena could be related to the black-to-white-hole transition [8]. Among these are fast radio bursts (FRBs) and certain high-energy cosmic rays. Both could be produced by matter and photons that were trapped in black holes produced in the early Universe and liberated by the black-to-white-hole transition. For the moment, however, the astrophysical data are insufficient to determine whether the statistical properties of observed FRBs and cosmic rays confirm this hypothesis [8]. Another intriguing possibility is that small holes produced by the black-to-white-hole transition may be stable: in which case, these “remnants” could be a component of dark matter [9].

We are only beginning to understand the quantum physics of black holes, but in this still speculative field, the Ashtekar-Olmedo-Singh result gives us a welcome fixed point: loop gravity predicts that the interior of a black hole continues into a white hole. The importance of any progress in this field goes beyond understanding black holes. The center of a black hole is where our current theory of spacetime, as given by Einstein’s general relativity, fails. Understanding the physics of this region would mean understanding quantum space and quantum time.

This research is published in Physical Review Letters and Physical Review D.

Hexbyte Hacker News Computers References

  1. A. Ashtekar, J. Olmedo, and P. Singh, “Quantum transfiguration of Kruskal black holes,” Phys. Rev. Lett. 121, 241301 (2018); “Quantum extension of the Kruskal spacetime,” Phys. Rev. D 98, 126003 (2018).
  2. E. Bianchi, M. Christodoulou, F. D’Ambrosio, H. M. Haggard, and C. Rovelli, “White holes as remnants: A surprising scenario for the end of a black hole,” Class. Quant. Grav. 35, 225003 (2018).
  3. J. L. Synge, “The gravitational field of a particle,” Proc. Roy. Irish Acad. A 53, 83 (1950).
  4. C. Rovelli and F. Vidotto, “Planck stars,” Int. J. Mod. Phys. D 23, 1442026 (2014).
  5. H. M. Haggard and C. Rovelli, “Quantum-gravity effects outside the horizon spark black to white hole tunneling,” Phys. Rev. D 92, 104020 (2015).
  6. L. Modesto, “Black hole interior from loop quantum gravity,” Adv. High Energy Phys. 2008, 459290 (2008).
  7. I. Agullo and P. Singh, “Loop quantum cosmology: A brief review,” Loop Quantum Gravity, 100 Years of General Relativity Vol. 4, edited by A. Ashtekar and J. Pullin (World Scientific, Singapore, 2017)[Amazon][WorldCat].
  8. A. Barrau, B. Bolliet, F. Vidotto, and C. Weimer, “Phenomenology of bouncing black holes in quantum gravity: A closer look,” J. Cosmol. Astropart. Phys. 2016, 022 (2016); A. Barrau, K. Martineau, and F. Moulin, “Status report on the phenomenology of black holes in loop quantum gravity: Evaporation, tunneling to white holes, dark matter and gravitational waves,” Universe 4, 102 (2018).
  9. C. Rovelli and F. Vidotto, “Small black/white hole stability and dark matter,” Universe 4, 127 (2018).

Hexbyte Hacker News Computers About the Author

Hexbyte  Hacker News  Computers Image of Carlo Rovelli

Carlo Rovelli received his Ph.D. from the University of Padova in 1986. He was on the faculty of the University of Pittsburgh from 1990 to 2000 and then went to the Aix-Marseille University in France, where he leads the quantum gravity research group. His activities range from quantum gravity to the foundations of quantum physics and the philosophy of physics. He has been awarded the 1995 Xanthopoulos Award, the Laurea Honoris Causa from the Universidad de San Martin, Buenos Aires, and the Honorary Professorship of the Beijing Normal University in China. He is a senior member of the Institut Universitaire de France and a member of the Académie Internationale de Philosophie des Sciences.


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Hexbyte  Tech News  Wired Watch the New ‘Men in Black International’ Trailer Now

Hexbyte Tech News Wired Watch the New ‘Men in Black International’ Trailer Now

Hexbyte Tech News Wired

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Tessa Thompson and Chris Hemsworth suit up in the new Men in Black International trailer.

Giles Keyte

It’s time for the final pre-holiday edition of The Monitor, WIRED’s roundup of the latest in the world of culture, from box-office news to announcements about hot new trailers. In today’s installment: the Men in Black are back; To All the Boys I’ve Loved Before is officially a Netflix franchise; and Aquaman is doing swimmingly at the box office.

Here Come the (New) Men in Black

“You are the best-kept secret in the universe,” notes Agent M, the newbie alien-seeker played by Tessa Thompson, in the first trailer for next summer’s Men in Black International. And for a while, this latest MiB entry was a bit of a mystery itself, with early rumors indicating it would be a crossover film featuring characters from Sony’s hit 21 Jump Street series. Instead, the first MiB sequel in seven years features Thompson teaming up with the veteran Agent H (Chris Hemsworth) in an attempt to thwart a new alien threat (helping them are higher-ups played by Liam Neeson and Emma Thompson). The action takes place in London, which we know because the trailer features a shot of a bridge in London, accompanied by Fergie’s “London Bridge.” What? No room for Will Smith’s 1997 theme song? It’s a glaring oversight—but we’ll let it slide, just this once.

To All the Boys I’ve Loved Before, Again

Netflix has confirmed it’s moving ahead with a sequel to this year’s To All the Boys I’ve Loved Before, the rom-com that proved to be a breakout hit for leads Lara Condon and Noah Centineo (both actors will return, as will original Boys screenwriter Sofia Alvarez). Adapted from a best-selling book trilogy by Jenny Han, Boys was all but inescapable over the summer, turning its cast members into social-media superstars, fueled in part by Netflix’s sizable teen audience. The streamer never reveals specific viewership figures, but if you want an idea of how big Boys became, we dare you to try standing in a high school parking lot with a sign offering “FREE NOAH CENTINEO SMOOCHES,” and see how long you last without getting trampled.

Aquaman Is About to Be Swimming in Cash

In case you were wondering, this weekend’s box office champ has already surfaced: Aquaman, which is expected to top the long pre-holiday weekend (the film’s already earned more than $250 million overseas, including a mighty opening in China). It will likely be followed by Disney’s Mary Poppins Returns and the Transformers spin-off Bumblebee, in what will be one of the most competitive Christmas openings in years—the first December without a new Star Wars movie since 2014. If Aquaman—which has earned mixed reviews—can sustain its commercial momentum, it will hint at a possibly not-terrible future for the big-screen DC Universe, which stumbled last year with Justice League, the big-budget, 120-minute-long MacBook screensaver that was accidentally released into theaters.


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Hexbyte  Hacker News  Computers The truth about Black Friday and Cyber Monday

Hexbyte Hacker News Computers The truth about Black Friday and Cyber Monday

Hexbyte Hacker News Computers

At Cloudflare we handle a lot of traffic on behalf of our customers. Something we all see and hear a lot about at this time of year are Black Friday (23 November this year) and Cyber Monday (26 November) – but just how important are these days on the Internet?

Black Friday by Per-Olof Forsberg, license: CC BY 2.0

To try and answer this question, we took a look at anonymised samples of HTTP requests crossing our network. First of all, let’s look at total page views from across our global network from the last few weeks and see if we can spot Black Friday and Cyber Monday:

All page views

So this is total page views by day (UTC) from November 19 (a week before Cyber Monday) until Monday December 3. Other than follow-the-sun fluctuations in a repeating daily pattern, each whole day is pretty similar in shape and size compared to the last. Black Friday and Cyber Monday aren’t visible in overall traffic patterns.

Get specific

We have a very diverse set of customers across 12 million domain names and not all of them are selling products or doing so directly online. To identify those websites that are, I used metadata from the wonderful HTTP Archive project to export a list of domains using Cloudflare that were also running ecommerce software.

Here are the page views for these ecommerce sites over the same time period:

Ecommerce page views

So we can see clearly that our ecommerce customers are seeing a big increase in page views on November 23 and 26. Black Friday and Cyber Monday are most certainly a thing. This year Black Friday was quite a bit busier than Cyber Monday – around 22% busier in terms of page views. If we compare the page views of each day to the week prior, we can see the changes clearly:

% page view change vs previous week

The uplift starts on Wednesday but really kicks in during Thanksgiving with an increase of more than 100% on Black Friday.

Browsing vs Buying

So we’ve established that these shopping days are important in terms of visitor activity. More pages are being viewed on these days – but is anyone buying anything?

We’re dealing with trillions of requests across a really large data set of different websites without any specific knowledge of what a purchase transaction would look like for each – so to approximate this I took a crude approach, which is to look for successful checkout interactions in the data. If you imagine a typical ecommerce application makes a purchase with a HTTP request like “POST /store/checkout HTTP/1.1” we can look for requests similar to this to understand the activity.

% of checkout interactions vs prior week

We can see here that Black Friday has an almost 200% increase in checkout interactions compared to the previous Friday.

Using this raw number of checkout interactions to compare with the page views we have something approximating a conversion %. This is not a true conversion figure – calculating a true conversion figure would require data that identifies individuals and detailed action tracking for each website. What we have is the total number of page views (HTTP requests that return HTML successfully) compared to the total number of POST requests to a checkout. This gives us a baseline to compare changes in “conversion” over these big November shopping days:

% of checkout interactions / page views vs prior week

Each bar on this chart represents the % change in checkout interactions as a proportion of page views compared to the same day the previous week. We can see this increased by 45% on Black Friday compared to the Friday before (boring old beige Friday November 16). The following Saturday was booming at 60% – because we’re dealing with time in UTC, a UTC Saturday actually includes Black Friday traffic for some parts of the world, the same can be said of Tuesday which contains overlap from Cyber Monday – we’ll break this down a bit later.

On Cyber Monday, the increase actually beats Black Friday, meaning page views lead to cart interactions 57% more often than the prior Monday (boring old vanilla Monday November 19), albeit from a lower number of transactions.

What devices are people buying on?

What we see here is just how much more browsing people do on mobiles today vs desktop, with mobile winning most days:

Page Views by Device Type

When it comes to checkout interactions though, we can see the situation is switched with visitors more likely to interact with the checkout on a desktop overall, but even more so on Black Friday (14% more likely) and Cyber Monday (20% more likely).

Checkout Interaction as % of Page Views

Let’s look at a specific region to understand more, starting with the US:

USA Page Views (PST)

We can see a more normal weekday pattern on the prior Thursday & Friday (15 & 16 Nov) whereby desktop page views eclipse mobile during the daytime while people are at their desks. In the evenings and weekends, mobile takes over. What we see from the 21st onward is evidence of people taking time off work and doing more with their mobile devices. Even on Thanksgiving, there is still a big rise in activity as people start gearing up for Friday’s deals or finding ways to avoid political discussion with relatives at home!

On Cyber Monday, traffic earlier in the day is lower as people return to work, however we are seeing heavy use of desktop devices. As the working day ends, mobile once again dominates. Things begin to settle back into a more regular pattern from Tuesday November 27 onwards.

Let’s take a look at checkout interaction over the Black Friday to Cyber Monday weekend by device type.

USA Checkout Interaction % (PST)

Despite all of that mobile browsing activity, desktop devices are more commonly used for checkout actions. People seem to browse more on mobile, committing to buy more often with desktop, it may also just be that mobile users have more distractions both on the device and in the real world and are therefore less likely to complete a purchase. From personal experience, I also think the poor mobile optimisation of some sites’ checkout flows make desktop preferrable – and when customers are incentivised with discounts & deals, they are more likely to switch devices to complete a transaction if they hit an issue.

Is Black Friday / Cyber Monday international?

It might be obvious if you’re reading this from the UK, but despite the fact that Thanksgiving is not a holiday here, retailers have very much picked up the mantle from US retailers and seized the opportunity to drive sales over this weekend.

UK Page Views (UTC)

Page views to ecommerce websites on Cloudflare look very similar in shape to the US on Black Friday. However, mobile is more dominant in the UK, even during working hours. It’s worth noting one big difference here – Cyber Monday in the UK was only 22% up in terms of page views compared to the prior Monday – in the US the increase was more than 4x that.

UK Checkout Interaction as % of Page Views

When it comes to checkout, it also looks like UK visitors to ecommerce sites commit more with their mobile, but desktop is still more likely to lead to more conversion.

Taking Germany as another example, here’s how page views look:

Germany Page Views (CET)

Desktop use during typical working hours is much more pronounced in Germany. Black Friday and Cyber Monday show higher page views than a normal Friday / Monday but the difference is much smaller than regions such as the US & UK.

Conclusions

Black Friday is spreading internationally despite these still being normal working days for the rest of the world. Cyber Monday is also increasing ecommerce activity internationally but tends to be quieter than Black Friday. Overall, mobile browsing eclipses desktop, but those desktop page views tend to lead to checkout more often.

Retailers should continue to invest in making their mobile & desktop ecommerce experiences fast & resilient to seize on these key days.

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