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What we know about CrowdStrike’s update fail that’s causing global outages and travel chaos

A faulty software update issued by security giant CrowdStrike has resulted in a massive overnight outage that’s affected Windows computers around the world , disrupting businesses, airports, train stations, banks, broadcasters and the healthcare sector.

CrowdStrike said the outage was not caused by a cyberattack, but was the result of a “defect” in a software update for its flagship security product, Falcon Sensor. The defect caused any Windows computers that Falcon is installed on to crash without fully loading.

“The issue has been identified, isolated and a fix has been deployed,” said CrowdStrike in a statement on Friday . Some businesses and organizations are beginning to recover, but many expect the outages to drag on into the weekend or next week given the complexity of the fix. CrowdStrike CEO George Kurtz told NBC News that it may take “some time for some systems that just automatically won’t recover.” In a later tweet , Kurtz apologized for the disruption.

Here’s everything you need to know about the outages.

What happened?

Late Thursday into Friday, reports began to emerge of IT problems wherein Windows computers were getting stuck with the infamous “blue screen of death” — a bright blue error screen with a message that displays when Windows encounters a critical failure, crashes or cannot load.

The outages were first noticed in Australia early on Friday, and reports quickly came in from the rest of Asia and Europe as the regions began their day, as well as the United States.

Within a short time, CrowdStrike confirmed that a software update for Falcon had malfunctioned and was causing Windows computers that had the software installed to crash. Falcon lets CrowdStrike remotely analyze and check for malicious threats and malware on installed computers.

At around the same time, Microsoft reported a significant outage at one of its most used Azure cloud regions covering much of the central United States. A spokesperson for Microsoft told TechCrunch that its outage was unrelated to CrowdStrike’s incident .

Around Friday noon (Eastern time), Microsoft CEO Satya Nadella posted on X saying the company is aware of the CrowdStrike botched update and is “working closely with CrowdStrike and across the industry to provide customers technical guidance and support to safely bring their systems back online.”

What is CrowdStrike and what does Falcon Sensor do?

CrowdStrike, founded in 2011, has quickly grown into a cybersecurity giant. Today the company provides software and services to 29,000 corporate customers, including around half of Fortune 500 companies, 43 out of 50 U.S. states and eight out of the top 10 tech firms, according to its website .

The company’s cybersecurity software, Falcon, is used by enterprises to manage security on millions of computers around the world. These businesses include large corporations, hospitals, transportation hubs and government departments. Most consumer devices do not run Falcon and are unaffected by this outage.

One of the company’s biggest recent claims to fame was when it caught a group of Russian government hackers breaking into the Democratic National Committee ahead of the 2016 U.S. presidential election. CrowdStrike is also known for using memorable animal-themed names for the hacking groups it tracks based on their nationality, such as: Fancy Bear , believed to be part of Russia’s General Staff Main Intelligence Directorate, or GRU; Cozy Bear , believed to be part of Russia’s Foreign Intelligence Service, or SVR; Gothic Panda , believed to be a Chinese government group; and Charming Kitten , believed to be an Iranian state-backed group. The company even makes action figures to represent these groups, which it sells as swag .

CrowdStrike is so big it’s one of the sponsors of the Mercedes F1 team , and this year even aired a Super Bowl ad — a first for a cybersecurity company. 

Who are the outages affecting?

Practically anyone who during their everyday life interacts with a computer system running software from CrowdStrike is affected, even if the computer isn’t theirs. 

These devices include the cash registers at grocery stores, departure boards at airports and train stations, school computers, your work-issued laptops and desktops, airport check-in systems, airlines’ own ticketing and scheduling platforms, healthcare networks and many more. Because CrowdStrike’s software is so ubiquitous, the outages are causing chaos around the world in a variety of ways. A single affected Windows computer in a fleet of systems could be enough to disrupt the network. 

TechCrunch reporters around the world are seeing and experiencing outages, including at points of travel, doctors’ offices and online. Early on Friday, the Federal Aviation Administration put in effect a ground stop, effectively grounding flights across the United States, citing the disruption. It looks like so far the national Amtrak rail network is functioning as normal. 

What is the U.S. government doing so far?

Given that the problem stems from a company, there isn’t much that the U.S. federal government can do. According to a pool report, President Biden was briefed on the CrowdStrike outage, and “his team is in touch with CrowdStrike and impacted entities.” That’s in large part because the federal government is a customer of CrowdStrike and also affected.

Several federal agencies are affected by the incident, including the Department of Education , and Social Security Administration, which said Friday that it closed its offices as a result of the outage.

The pool report said Biden’s team is “engaged across the interagency to get sector by sector updates throughout the day and is standing by to provide assistance as needed.” 

In a separate tweet, Homeland Security said it was working with its U.S. cybersecurity agency CISA, CrowdStrike and Microsoft — as well as its federal, state, local and critical infrastructure partners — to “fully assess and address system outages.”

There will no doubt be questions for CrowdStrike (and to some extent Microsoft, whose unrelated outage also caused disruption overnight for its customers) from government and congressional investigators. 

For now, the immediate focus will be on the recovery of affected systems.

How do affected customers fix their Windows computers?

The major problem here is that CrowdStrike’s Falcon Sensor software malfunctioned, causing Windows machines to crash, and there’s no easy way to fix that. 

So far, CrowdStrike has issued a patch, and it has also detailed a workaround that could help affected systems function normally until it has a permanent solution. One option is for users to “reboot the [affected computer] to give it an opportunity to download the reverted channel file,” referring to the fixed file.

In a message to users , CrowdStrike detailed a few steps customers can take, one of which requires physical access to an affected system to remove the defective file. CrowdStrike says users should boot the computer into Safe Mode or Windows Recovery Environment, navigate to the CrowdStrike directory, and delete the faulty file “C-00000291*.sys.”

The wider problem with having to fix the file manually could be a major headache for companies and organizations with large numbers of computers, or Windows-powered servers in datacenters or locations that might be in another region, or an entirely different country.

CISA warns that malicious actors are ‘taking advantage’ of the outage

In a statement on Friday, CISA attributed the outages to the faulty CrowdStrike update and that the issue was not due to a cyberattack. CISA said that it was “working closely with CrowdStrike and federal, state, local, tribal and territorial partners, as well as critical infrastructure and international partners to assess impacts and support remediation efforts.”

CISA did note, however, that it has “observed threat actors taking advantage of this incident for phishing and other malicious activity.” The cybersecurity agency did not provide more specifics, but warned organizations to stay vigilant.

Malicious actors can and will exploit confusion and chaos to carry out cyberattacks on their own. Rachel Tobac, a social engineering expert and founder of cybersecurity firm SocialProof Security, said in a series of posts on X to “verify people are who they say they are before taking sensitive actions.”

“Criminals will attempt to use this IT outage to pretend to be IT to you or you to IT to steal access, passwords, codes, etc.,” Tobac said.

What do we know about misinformation so far?

It’s easy to understand why some might have thought that this outage was a cyberattack. Sudden outages, blue screens at airports, office computers filled with error messages, and chaos and confusion. As you might expect, a fair amount of misinformation is already flying around , even as social media sites incorrectly flag trending topics like “cyberattack.”

Remember to check official sources of news and information, and if something seems too good to be true, it might just well be.

TechCrunch will keep this report updated throughout the day.

TechCrunch’s Ram Iyer contributed reporting.

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Faulty CrowdStrike update causes major global IT outage, taking out banks, airlines and businesses globally

Security giant CrowdStrike said the outage was not caused by a cyberattack, as businesses anticipate widespread disruption.

US cyber agency CISA says malicious hackers are ‘taking advantage’ of CrowdStrike outage

CISA confirmed the CrowdStrike outage was not caused by a cyberattack, but urged caution as malicious hackers exploit the situation.

These startups are trying to prevent another CrowdStrike-like outage, according to VCs

The global outage is a perfect reminder how much of the world relies on technological infrastructure.

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Twitch reinstates Trump’s account ahead of the 2024 presidential election

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This week, Google is in discussions to pay $23 billion for cloud security startup Wiz, SoftBank acquires Graphcore, and more.

CrowdStrike’s rivals stand to benefit from its update fail debacle

CrowdStrike competes with a number of vendors, including SentinelOne and Palo Alto Networks but also Microsoft, Trellix, Trend Micro and Sophos, in the endpoint security market.

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Here’s everything you need to know so far about the global outages caused by CrowdStrike’s buggy software update.

From the Sphere to false cyberattack claims, misinformation runs rampant amid CrowdStrike outage

This serves as an example for how easy it is to spread inaccurate information online during a time of immense global confusion and panic.

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When is the 2024 RNC? Full week schedule, dates, times, where to watch and livestream

The 2024 Republican National Convention kicks off Monday in Milwaukee, Wisconsin, in the wake of presumptive GOP presidential nominee Donald Trump surviving an assassination attempt .

The four-day event begins just days after shots were fired in Trump's direction at his rally in Butler, Pennsylvania, killing a rally attendee and wounding two others. The gunman, identified as Thomas Crooks , 20, was killed by Secret Service agents moments later.

Trump announced his pick for vice president, Ohio Sen. J.D. Vance , and the 78-year-old is expected to be officially nominated by the party for president at the convention. He is currently scheduled to address delegates on Thursday evening, the last day of the convention.

Here's everything you need to know about the 2024 Republican National Convention.

RNC 2024 live updates: Trump stresses new theme after shooting

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When is the 2024 RNC?

The RNC is scheduled to run from July 15-18.

How to watch and stream 2024 RNC

The RNC will livestream events across multiple online platforms.

USA TODAY will provide livestream coverage on YouTube each night of the RNC, Monday through Thursday.

The RNC will stream events live on platforms including YouTube and X.

Each television network will handle coverage slightly differently. Here's a breakdown of the major networks and their coverage plans for the RNC:

• C-SPAN will carry the entire convention uninterrupted for all four days.
• CBS television stations will have live coverage starting at 10 p.m. ET all four days.
• NBC News will broadcast "Decision 2024" live during the same time it streams the program, from 10 p.m. to 11 p.m. the first two nights of the convention, and from 9 p.m. to 11 p.m. the final two nights.
• ABC News will have live coverage from 10 p.m. to 11 p.m. all four days on its main broadcast network, hosted by David Muir.
• Fox News will air coverage during its regular prime-time lineup of shows, and will broadcast a nightly one-hour special starting at 10 p.m., hosted by Bret Baier and Martha MacCallum.
• CNN will air live coverage beginning at 2 p.m. Monday, before Trump is expected to be formally nominated via a roll call. The network will then have a combination of coverage and analysis each night from 8 p.m. to midnight, anchored by Jake Tapper and Anderson Cooper.
• MSNBC will broadcast a prime-time special from 8 p.m. to 10 p.m. Tuesday, hosted by Rachel Maddow. The network will have coverage from 8 p.m. to midnight on Wednesday and Thursday.

Full 2024 RNC schedule

Will donald trump speak at the 2024 rnc.

Yes, Trump is scheduled to address delegates on Thursday evening.

"President Trump looks forward to joining you all in Milwaukee as we proceed with our convention to nominate him to serve as the 47th President of the United States. As our party's nominee, President Trump will continue to share his vision to Make America Great Again," the RNC and the Trump campaign said in a joint statement issued Saturday.

Who else is speaking at the 2024 RNC?

So far, the list of official speakers who have confirmed they're slated to take the stage in Milwaukee this week includes Florida Gov. Ron DeSantis, former reality TV star Amber Rose, Indiana Congressman Jim Banks, and Donald Trump Jr., among others.

Iowa’s Republican Party Chair Jeff Kaufmann will deliver the RNC’s speech formally nominating Donald Trump for president,  the Des Moines Register reported Thursday .

RNC 2024: See full list of speakers

What will security look like at the 2024 RNC?

U.S. Secret Service Director Kimberly Cheatle said in a news release Monday the agency has "reviewed and strengthened" its security plan for the RNC in the wake of Saturday's shooting.

"The security plans for National Special Security Events are designed to be flexible," Cheatle said in the news release. "As the conventions progress, and in accordance with the direction of the President, the Secret Service will continuously adapt our operations as necessary in order to ensure the highest level of safety and security for convention attendees, volunteers and the City of Milwaukee."

"In addition to the additional security enhancements we provided former President Trump's detail in June, we have also implemented changes to his security detail since Saturday to ensure his continued protection for the convention and the remainder of the campaign," Cheatle said.

Contributing: Kathryn Palmer, Victoria Moorwood and Trevor Hughes, USA TODAY Network

Gabe Hauari is a national trending news reporter at USA TODAY. You can follow him on X  @GabeHauari  or email him at [email protected].

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Time Travel

There is an extensive literature on time travel in both philosophy and physics. Part of the great interest of the topic stems from the fact that reasons have been given both for thinking that time travel is physically possible—and for thinking that it is logically impossible! This entry deals primarily with philosophical issues; issues related to the physics of time travel are covered in the separate entries on time travel and modern physics and time machines . We begin with the definitional question: what is time travel? We then turn to the major objection to the possibility of backwards time travel: the Grandfather paradox. Next, issues concerning causation are discussed—and then, issues in the metaphysics of time and change. We end with a discussion of the question why, if backwards time travel will ever occur, we have not been visited by time travellers from the future.

1.1 Time Discrepancy

1.2 changing the past, 2.1 can and cannot, 2.2 improbable coincidences, 2.3 inexplicable occurrences, 3.1 backwards causation, 3.2 causal loops, 4.1 time travel and time, 4.2 time travel and change, 5. where are the time travellers, other internet resources, related entries, 1. what is time travel.

There is a number of rather different scenarios which would seem, intuitively, to count as ‘time travel’—and a number of scenarios which, while sharing certain features with some of the time travel cases, seem nevertheless not to count as genuine time travel: [ 1 ]

Time travel Doctor . Doctor Who steps into a machine in 2024. Observers outside the machine see it disappear. Inside the machine, time seems to Doctor Who to pass for ten minutes. Observers in 1984 (or 3072) see the machine appear out of nowhere. Doctor Who steps out. [ 2 ] Leap . The time traveller takes hold of a special device (or steps into a machine) and suddenly disappears; she appears at an earlier (or later) time. Unlike in Doctor , the time traveller experiences no lapse of time between her departure and arrival: from her point of view, she instantaneously appears at the destination time. [ 3 ] Putnam . Oscar Smith steps into a machine in 2024. From his point of view, things proceed much as in Doctor : time seems to Oscar Smith to pass for a while; then he steps out in 1984. For observers outside the machine, things proceed differently. Observers of Oscar’s arrival in the past see a time machine suddenly appear out of nowhere and immediately divide into two copies of itself: Oscar Smith steps out of one; and (through the window) they see inside the other something that looks just like what they would see if a film of Oscar Smith were played backwards (his hair gets shorter; food comes out of his mouth and goes back into his lunch box in a pristine, uneaten state; etc.). Observers of Oscar’s departure from the future do not simply see his time machine disappear after he gets into it: they see it collide with the apparently backwards-running machine just described, in such a way that both are simultaneously annihilated. [ 4 ] Gödel . The time traveller steps into an ordinary rocket ship (not a special time machine) and flies off on a certain course. At no point does she disappear (as in Leap ) or ‘turn back in time’ (as in Putnam )—yet thanks to the overall structure of spacetime (as conceived in the General Theory of Relativity), the traveller arrives at a point in the past (or future) of her departure. (Compare the way in which someone can travel continuously westwards, and arrive to the east of her departure point, thanks to the overall curved structure of the surface of the earth.) [ 5 ] Einstein . The time traveller steps into an ordinary rocket ship and flies off at high speed on a round trip. When he returns to Earth, thanks to certain effects predicted by the Special Theory of Relativity, only a very small amount of time has elapsed for him—he has aged only a few months—while a great deal of time has passed on Earth: it is now hundreds of years in the future of his time of departure. [ 6 ] Not time travel Sleep . One is very tired, and falls into a deep sleep. When one awakes twelve hours later, it seems from one’s own point of view that hardly any time has passed. Coma . One is in a coma for a number of years and then awakes, at which point it seems from one’s own point of view that hardly any time has passed. Cryogenics . One is cryogenically frozen for hundreds of years. Upon being woken, it seems from one’s own point of view that hardly any time has passed. Virtual . One enters a highly realistic, interactive virtual reality simulator in which some past era has been recreated down to the finest detail. Crystal . One looks into a crystal ball and sees what happened at some past time, or will happen at some future time. (Imagine that the crystal ball really works—like a closed-circuit security monitor, except that the vision genuinely comes from some past or future time. Even so, the person looking at the crystal ball is not thereby a time traveller.) Waiting . One enters one’s closet and stays there for seven hours. When one emerges, one has ‘arrived’ seven hours in the future of one’s ‘departure’. Dateline . One departs at 8pm on Monday, flies for fourteen hours, and arrives at 10pm on Monday.

A satisfactory definition of time travel would, at least, need to classify the cases in the right way. There might be some surprises—perhaps, on the best definition of ‘time travel’, Cryogenics turns out to be time travel after all—but it should certainly be the case, for example, that Gödel counts as time travel and that Sleep and Waiting do not. [ 7 ]

In fact there is no entirely satisfactory definition of ‘time travel’ in the literature. The most popular definition is the one given by Lewis (1976, 145–6):

What is time travel? Inevitably, it involves a discrepancy between time and time. Any traveller departs and then arrives at his destination; the time elapsed from departure to arrival…is the duration of the journey. But if he is a time traveller, the separation in time between departure and arrival does not equal the duration of his journey.…How can it be that the same two events, his departure and his arrival, are separated by two unequal amounts of time?…I reply by distinguishing time itself, external time as I shall also call it, from the personal time of a particular time traveller: roughly, that which is measured by his wristwatch. His journey takes an hour of his personal time, let us say…But the arrival is more than an hour after the departure in external time, if he travels toward the future; or the arrival is before the departure in external time…if he travels toward the past.

This correctly excludes Waiting —where the length of the ‘journey’ precisely matches the separation between ‘arrival’ and ‘departure’—and Crystal , where there is no journey at all—and it includes Doctor . It has trouble with Gödel , however—because when the overall structure of spacetime is as twisted as it is in the sort of case Gödel imagined, the notion of external time (“time itself”) loses its grip.

Another definition of time travel that one sometimes encounters in the literature (Arntzenius, 2006, 602) (Smeenk and Wüthrich, 2011, 5, 26) equates time travel with the existence of CTC’s: closed timelike curves. A curve in this context is a line in spacetime; it is timelike if it could represent the career of a material object; and it is closed if it returns to its starting point (i.e. in spacetime—not merely in space). This now includes Gödel —but it excludes Einstein .

The lack of an adequate definition of ‘time travel’ does not matter for our purposes here. [ 8 ] It suffices that we have clear cases of (what would count as) time travel—and that these cases give rise to all the problems that we shall wish to discuss.

Some authors (in philosophy, physics and science fiction) consider ‘time travel’ scenarios in which there are two temporal dimensions (e.g. Meiland (1974)), and others consider scenarios in which there are multiple ‘parallel’ universes—each one with its own four-dimensional spacetime (e.g. Deutsch and Lockwood (1994)). There is a question whether travelling to another version of 2001 (i.e. not the very same version one experienced in the past)—a version at a different point on the second time dimension, or in a different parallel universe—is really time travel, or whether it is more akin to Virtual . In any case, this kind of scenario does not give rise to many of the problems thrown up by the idea of travelling to the very same past one experienced in one’s younger days. It is these problems that form the primary focus of the present entry, and so we shall not have much to say about other kinds of ‘time travel’ scenario in what follows.

One objection to the possibility of time travel flows directly from attempts to define it in anything like Lewis’s way. The worry is that because time travel involves “a discrepancy between time and time”, time travel scenarios are simply incoherent. The time traveller traverses thirty years in one year; she is 51 years old 21 years after her birth; she dies at the age of 100, 200 years before her birth; and so on. The objection is that these are straightforward contradictions: the basic description of what time travel involves is inconsistent; therefore time travel is logically impossible. [ 9 ]

There must be something wrong with this objection, because it would show Einstein to be logically impossible—whereas this sort of future-directed time travel has actually been observed (albeit on a much smaller scale—but that does not affect the present point) (Hafele and Keating, 1972b,a). The most common response to the objection is that there is no contradiction because the interval of time traversed by the time traveller and the duration of her journey are measured with respect to different frames of reference: there is thus no reason why they should coincide. A similar point applies to the discrepancy between the time elapsed since the time traveller’s birth and her age upon arrival. There is no more of a contradiction here than in the fact that Melbourne is both 800 kilometres away from Sydney—along the main highway—and 1200 kilometres away—along the coast road. [ 10 ]

Before leaving the question ‘What is time travel?’ we should note the crucial distinction between changing the past and participating in (aka affecting or influencing) the past. [ 11 ] In the popular imagination, backwards time travel would allow one to change the past: to right the wrongs of history, to prevent one’s younger self doing things one later regretted, and so on. In a model with a single past, however, this idea is incoherent: the very description of the case involves a contradiction (e.g. the time traveller burns all her diaries at midnight on her fortieth birthday in 1976, and does not burn all her diaries at midnight on her fortieth birthday in 1976). It is not as if there are two versions of the past: the original one, without the time traveller present, and then a second version, with the time traveller playing a role. There is just one past—and two perspectives on it: the perspective of the younger self, and the perspective of the older time travelling self. If these perspectives are inconsistent (e.g. an event occurs in one but not the other) then the time travel scenario is incoherent.

This means that time travellers can do less than we might have hoped: they cannot right the wrongs of history; they cannot even stir a speck of dust on a certain day in the past if, on that day, the speck was in fact unmoved. But this does not mean that time travellers must be entirely powerless in the past: while they cannot do anything that did not actually happen, they can (in principle) do anything that did happen. Time travellers cannot change the past: they cannot make it different from the way it was—but they can participate in it: they can be amongst the people who did make the past the way it was. [ 12 ]

What about models involving two temporal dimensions, or parallel universes—do they allow for coherent scenarios in which the past is changed? [ 13 ] There is certainly no contradiction in saying that the time traveller burns all her diaries at midnight on her fortieth birthday in 1976 in universe 1 (or at hypertime A ), and does not burn all her diaries at midnight on her fortieth birthday in 1976 in universe 2 (or at hypertime B ). The question is whether this kind of story involves changing the past in the sense originally envisaged: righting the wrongs of history, preventing subsequently regretted actions, and so on. Goddu (2003) and van Inwagen (2010) argue that it does (in the context of particular hypertime models), while Smith (1997, 365–6; 2015) argues that it does not: that it involves avoiding the past—leaving it untouched while travelling to a different version of the past in which things proceed differently.

2. The Grandfather Paradox

The most important objection to the logical possibility of backwards time travel is the so-called Grandfather paradox. This paradox has actually convinced many people that backwards time travel is impossible:

The dead giveaway that true time-travel is flatly impossible arises from the well-known “paradoxes” it entails. The classic example is “What if you go back into the past and kill your grandfather when he was still a little boy?”…So complex and hopeless are the paradoxes…that the easiest way out of the irrational chaos that results is to suppose that true time-travel is, and forever will be, impossible. (Asimov 1995 [2003, 276–7]) travel into one’s past…would seem to give rise to all sorts of logical problems, if you were able to change history. For example, what would happen if you killed your parents before you were born. It might be that one could avoid such paradoxes by some modification of the concept of free will. But this will not be necessary if what I call the chronology protection conjecture is correct: The laws of physics prevent closed timelike curves from appearing . (Hawking, 1992, 604) [ 14 ]

The paradox comes in different forms. Here’s one version:

If time travel was logically possible then the time traveller could return to the past and in a suicidal rage destroy his time machine before it was completed and murder his younger self. But if this was so a necessary condition for the time trip to have occurred at all is removed, and we should then conclude that the time trip did not occur. Hence if the time trip did occur, then it did not occur. Hence it did not occur, and it is necessary that it did not occur. To reply, as it is standardly done, that our time traveller cannot change the past in this way, is a petitio principii . Why is it that the time traveller is constrained in this way? What mysterious force stills his sudden suicidal rage? (Smith, 1985, 58)

The idea is that backwards time travel is impossible because if it occurred, time travellers would attempt to do things such as kill their younger selves (or their grandfathers etc.). We know that doing these things—indeed, changing the past in any way—is impossible. But were there time travel, there would then be nothing left to stop these things happening. If we let things get to the stage where the time traveller is facing Grandfather with a loaded weapon, then there is nothing left to prevent the impossible from occurring. So we must draw the line earlier: it must be impossible for someone to get into this situation at all; that is, backwards time travel must be impossible.

In order to defend the possibility of time travel in the face of this argument we need to show that time travel is not a sure route to doing the impossible. So, given that a time traveller has gone to the past and is facing Grandfather, what could stop her killing Grandfather? Some science fiction authors resort to the idea of chaperones or time guardians who prevent time travellers from changing the past—or to mysterious forces of logic. But it is hard to take these ideas seriously—and more importantly, it is hard to make them work in detail when we remember that changing the past is impossible. (The chaperone is acting to ensure that the past remains as it was—but the only reason it ever was that way is because of his very actions.) [ 15 ] Fortunately there is a better response—also to be found in the science fiction literature, and brought to the attention of philosophers by Lewis (1976). What would stop the time traveller doing the impossible? She would fail “for some commonplace reason”, as Lewis (1976, 150) puts it. Her gun might jam, a noise might distract her, she might slip on a banana peel, etc. Nothing more than such ordinary occurrences is required to stop the time traveller killing Grandfather. Hence backwards time travel does not entail the occurrence of impossible events—and so the above objection is defused.

A problem remains. Suppose Tim, a time-traveller, is facing his grandfather with a loaded gun. Can Tim kill Grandfather? On the one hand, yes he can. He is an excellent shot; there is no chaperone to stop him; the laws of logic will not magically stay his hand; he hates Grandfather and will not hesitate to pull the trigger; etc. On the other hand, no he can’t. To kill Grandfather would be to change the past, and no-one can do that (not to mention the fact that if Grandfather died, then Tim would not have been born). So we have a contradiction: Tim can kill Grandfather and Tim cannot kill Grandfather. Time travel thus leads to a contradiction: so it is impossible.

Note the difference between this version of the Grandfather paradox and the version considered above. In the earlier version, the contradiction happens if Tim kills Grandfather. The solution was to say that Tim can go into the past without killing Grandfather—hence time travel does not entail a contradiction. In the new version, the contradiction happens as soon as Tim gets to the past. Of course Tim does not kill Grandfather—but we still have a contradiction anyway: for he both can do it, and cannot do it. As Lewis puts it:

Could a time traveler change the past? It seems not: the events of a past moment could no more change than numbers could. Yet it seems that he would be as able as anyone to do things that would change the past if he did them. If a time traveler visiting the past both could and couldn’t do something that would change it, then there cannot possibly be such a time traveler. (Lewis, 1976, 149)

Lewis’s own solution to this problem has been widely accepted. [ 16 ] It turns on the idea that to say that something can happen is to say that its occurrence is compossible with certain facts, where context determines (more or less) which facts are the relevant ones. Tim’s killing Grandfather in 1921 is compossible with the facts about his weapon, training, state of mind, and so on. It is not compossible with further facts, such as the fact that Grandfather did not die in 1921. Thus ‘Tim can kill Grandfather’ is true in one sense (relative to one set of facts) and false in another sense (relative to another set of facts)—but there is no single sense in which it is both true and false. So there is no contradiction here—merely an equivocation.

Another response is that of Vihvelin (1996), who argues that there is no contradiction here because ‘Tim can kill Grandfather’ is simply false (i.e. contra Lewis, there is no legitimate sense in which it is true). According to Vihvelin, for ‘Tim can kill Grandfather’ to be true, there must be at least some occasions on which ‘If Tim had tried to kill Grandfather, he would or at least might have succeeded’ is true—but, Vihvelin argues, at any world remotely like ours, the latter counterfactual is always false. [ 17 ]

Return to the original version of the Grandfather paradox and Lewis’s ‘commonplace reasons’ response to it. This response engenders a new objection—due to Horwich (1987)—not to the possibility but to the probability of backwards time travel.

Think about correlated events in general. Whenever we see two things frequently occurring together, this is because one of them causes the other, or some third thing causes both. Horwich calls this the Principle of V-Correlation:

if events of type A and B are associated with one another, then either there is always a chain of events between them…or else we find an earlier event of type C that links up with A and B by two such chains of events. What we do not see is…an inverse fork—in which A and B are connected only with a characteristic subsequent event, but no preceding one. (Horwich, 1987, 97–8)

For example, suppose that two students turn up to class wearing the same outfits. That could just be a coincidence (i.e. there is no common cause, and no direct causal link between the two events). If it happens every week for the whole semester, it is possible that it is a coincidence, but this is extremely unlikely . Normally, we see this sort of extensive correlation only if either there is a common cause (e.g. both students have product endorsement deals with the same clothing company, or both slavishly copy the same influencer) or a direct causal link (e.g. one student is copying the other).

Now consider the time traveller setting off to kill her younger self. As discussed, no contradiction need ensue—this is prevented not by chaperones or mysterious forces, but by a run of ordinary occurrences in which the trigger falls off the time traveller’s gun, a gust of wind pushes her bullet off course, she slips on a banana peel, and so on. But now consider this run of ordinary occurrences. Whenever the time traveller contemplates auto-infanticide, someone nearby will drop a banana peel ready for her to slip on, or a bird will begin to fly so that it will be in the path of the time traveller’s bullet by the time she fires, and so on. In general, there will be a correlation between auto-infanticide attempts and foiling occurrences such as the presence of banana peels—and this correlation will be of the type that does not involve a direct causal connection between the correlated events or a common cause of both. But extensive correlations of this sort are, as we saw, extremely rare—so backwards time travel will happen about as often as you will see two people wear the same outfits to class every day of semester, without there being any causal connection between what one wears and what the other wears.

We can set out Horwich’s argument this way:

• If time travel were ever to occur, we should see extensive uncaused correlations.
• It is extremely unlikely that we should ever see extensive uncaused correlations.
• Therefore time travel is extremely unlikely to occur.

The conclusion is not that time travel is impossible, but that we should treat it the way we treat the possibility of, say, tossing a fair coin and getting heads one thousand times in a row. As Price (1996, 278 n.7) puts it—in the context of endorsing Horwich’s conclusion: “the hypothesis of time travel can be made to imply propositions of arbitrarily low probability. This is not a classical reductio, but it is as close as science ever gets.”

Smith (1997) attacks both premisses of Horwich’s argument. Against the first premise, he argues that backwards time travel, in itself, does not entail extensive uncaused correlations. Rather, when we look more closely, we see that time travel scenarios involving extensive uncaused correlations always build in prior coincidences which are themselves highly unlikely. Against the second premise, he argues that, from the fact that we have never seen extensive uncaused correlations, it does not follow that we never shall. This is not inductive scepticism: let us assume (contra the inductive sceptic) that in the absence of any specific reason for thinking things should be different in the future, we are entitled to assume they will continue being the same; still we cannot dismiss a specific reason for thinking the future will be a certain way simply on the basis that things have never been that way in the past. You might reassure an anxious friend that the sun will certainly rise tomorrow because it always has in the past—but you cannot similarly refute an astronomer who claims to have discovered a specific reason for thinking that the earth will stop rotating overnight.

Sider (2002, 119–20) endorses Smith’s second objection. Dowe (2003) criticises Smith’s first objection, but agrees with the second, concluding overall that time travel has not been shown to be improbable. Ismael (2003) reaches a similar conclusion. Goddu (2007) criticises Smith’s first objection to Horwich. Further contributions to the debate include Arntzenius (2006), Smeenk and Wüthrich (2011, §2.2) and Elliott (2018). For other arguments to the same conclusion as Horwich’s—that time travel is improbable—see Ney (2000) and Effingham (2020).

Return again to the original version of the Grandfather paradox and Lewis’s ‘commonplace reasons’ response to it. This response engenders a further objection. The autoinfanticidal time traveller is attempting to do something impossible (render herself permanently dead from an age younger than her age at the time of the attempts). Suppose we accept that she will not succeed and that what will stop her is a succession of commonplace occurrences. The previous objection was that such a succession is improbable . The new objection is that the exclusion of the time traveler from successfully committing auto-infanticide is mysteriously inexplicable . The worry is as follows. Each particular event that foils the time traveller is explicable in a perfectly ordinary way; but the inevitable combination of these events amounts to a ring-fencing of the forbidden zone of autoinfanticide—and this ring-fencing is mystifying. It’s like a grand conspiracy to stop the time traveler from doing what she wants to do—and yet there are no conspirators: no time lords, no magical forces of logic. This is profoundly perplexing. Riggs (1997, 52) writes: “Lewis’s account may do for a once only attempt, but is untenable as a general explanation of Tim’s continual lack of success if he keeps on trying.” Ismael (2003, 308) writes: “Considered individually, there will be nothing anomalous in the explanations…It is almost irresistible to suppose, however, that there is something anomalous in the cases considered collectively, i.e., in our unfailing lack of success.” See also Gorovitz (1964, 366–7), Horwich (1987, 119–21) and Carroll (2010, 86).

There have been two different kinds of defense of time travel against the objection that it involves mysteriously inexplicable occurrences. Baron and Colyvan (2016, 70) agree with the objectors that a purely causal explanation of failure—e.g. Tim fails to kill Grandfather because first he slips on a banana peel, then his gun jams, and so on—is insufficient. However they argue that, in addition, Lewis offers a non-causal—a logical —explanation of failure: “What explains Tim’s failure to kill his grandfather, then, is something about logic; specifically: Tim fails to kill his grandfather because the law of non-contradiction holds.” Smith (2017) argues that the appearance of inexplicability is illusory. There are no scenarios satisfying the description ‘a time traveller commits autoinfanticide’ (or changes the past in any other way) because the description is self-contradictory (e.g. it involves the time traveller permanently dying at 20 and also being alive at 40). So whatever happens it will not be ‘that’. There is literally no way for the time traveller not to fail. Hence there is no need for—or even possibility of—a substantive explanation of why failure invariably occurs, and such failure is not perplexing.

3. Causation

Backwards time travel scenarios give rise to interesting issues concerning causation. In this section we examine two such issues.

Earlier we distinguished changing the past and affecting the past, and argued that while the former is impossible, backwards time travel need involve only the latter. Affecting the past would be an example of backwards causation (i.e. causation where the effect precedes its cause)—and it has been argued that this too is impossible, or at least problematic. [ 18 ] The classic argument against backwards causation is the bilking argument . [ 19 ] Faced with the claim that some event A causes an earlier event B , the proponent of the bilking objection recommends an attempt to decorrelate A and B —that is, to bring about A in cases in which B has not occurred, and to prevent A in cases in which B has occurred. If the attempt is successful, then B often occurs despite the subsequent nonoccurrence of A , and A often occurs without B occurring, and so A cannot be the cause of B . If, on the other hand, the attempt is unsuccessful—if, that is, A cannot be prevented when B has occurred, nor brought about when B has not occurred—then, it is argued, it must be B that is the cause of A , rather than vice versa.

The bilking procedure requires repeated manipulation of event A . Thus, it cannot get under way in cases in which A is either unrepeatable or unmanipulable. Furthermore, the procedure requires us to know whether or not B has occurred, prior to manipulating A —and thus, it cannot get under way in cases in which it cannot be known whether or not B has occurred until after the occurrence or nonoccurrence of A (Dummett, 1964). These three loopholes allow room for many claims of backwards causation that cannot be touched by the bilking argument, because the bilking procedure cannot be performed at all. But what about those cases in which it can be performed? If the procedure succeeds—that is, A and B are decorrelated—then the claim that A causes B is refuted, or at least weakened (depending upon the details of the case). But if the bilking attempt fails, it does not follow that it must be B that is the cause of A , rather than vice versa. Depending upon the situation, that B causes A might become a viable alternative to the hypothesis that A causes B —but there is no reason to think that this alternative must always be the superior one. For example, suppose that I see a photo of you in a paper dated well before your birth, accompanied by a report of your arrival from the future. I now try to bilk your upcoming time trip—but I slip on a banana peel while rushing to push you away from your time machine, my time travel horror stories only inspire you further, and so on. Or again, suppose that I know that you were not in Sydney yesterday. I now try to get you to go there in your time machine—but first I am struck by lightning, then I fall down a manhole, and so on. What does all this prove? Surely not that your arrival in the past causes your departure from the future. Depending upon the details of the case, it seems that we might well be entitled to describe it as involving backwards time travel and backwards causation. At least, if we are not so entitled, this must be because of other facts about the case: it would not follow simply from the repeated coincidental failures of my bilking attempts.

Backwards time travel would apparently allow for the possibility of causal loops, in which things come from nowhere. The things in question might be objects—imagine a time traveller who steals a time machine from the local museum in order to make his time trip and then donates the time machine to the same museum at the end of the trip (i.e. in the past). In this case the machine itself is never built by anyone—it simply exists. The things in question might be information—imagine a time traveller who explains the theory behind time travel to her younger self: theory that she herself knows only because it was explained to her in her youth by her time travelling older self. The things in question might be actions. Imagine a time traveller who visits his younger self. When he encounters his younger self, he suddenly has a vivid memory of being punched on the nose by a strange visitor. He realises that this is that very encounter—and resignedly proceeds to punch his younger self. Why did he do it? Because he knew that it would happen and so felt that he had to do it—but he only knew it would happen because he in fact did it. [ 20 ]

One might think that causal loops are impossible—and hence that insofar as backwards time travel entails such loops, it too is impossible. [ 21 ] There are two issues to consider here. First, does backwards time travel entail causal loops? Lewis (1976, 148) raises the question whether there must be causal loops whenever there is backwards causation; in response to the question, he says simply “I am not sure.” Mellor (1998, 131) appears to claim a positive answer to the question. [ 22 ] Hanley (2004, 130) defends a negative answer by telling a time travel story in which there is backwards time travel and backwards causation, but no causal loops. [ 23 ] Monton (2009) criticises Hanley’s counterexample, but also defends a negative answer via different counterexamples. Effingham (2020) too argues for a negative answer.

Second, are causal loops impossible, or in some other way objectionable? One objection is that causal loops are inexplicable . There have been two main kinds of response to this objection. One is to agree but deny that this is a problem. Lewis (1976, 149) accepts that a loop (as a whole) would be inexplicable—but thinks that this inexplicability (like that of the Big Bang or the decay of a tritium atom) is merely strange, not impossible. In a similar vein, Meyer (2012, 263) argues that if someone asked for an explanation of a loop (as a whole), “the blame would fall on the person asking the question, not on our inability to answer it.” The second kind of response (Hanley, 2004, §5) is to deny that (all) causal loops are inexplicable. A second objection to causal loops, due to Mellor (1998, ch.12), is that in such loops the chances of events would fail to be related to their frequencies in accordance with the law of large numbers. Berkovitz (2001) and Dowe (2001) both argue that Mellor’s objection fails to establish the impossibility of causal loops. [ 24 ] Effingham (2020) considers—and rebuts—some additional objections to the possibility of causal loops.

4. Time and Change

Gödel (1949a [1990a])—in which Gödel presents models of Einstein’s General Theory of Relativity in which there exist CTC’s—can well be regarded as initiating the modern academic literature on time travel, in both philosophy and physics. In a companion paper, Gödel discusses the significance of his results for more general issues in the philosophy of time (Gödel 1949b [1990b]). For the succeeding half century, the time travel literature focussed predominantly on objections to the possibility (or probability) of time travel. More recently, however, there has been renewed interest in the connections between time travel and more general issues in the metaphysics of time and change. We examine some of these in the present section. [ 25 ]

The first thing that we need to do is set up the various metaphysical positions whose relationships with time travel will then be discussed. Consider two metaphysical questions:

• Are the past, present and future equally real?
• Is there an objective flow or passage of time, and an objective now?

We can label some views on the first question as follows. Eternalism is the view that past and future times, objects and events are just as real as the present time and present events and objects. Nowism is the view that only the present time and present events and objects exist. Now-and-then-ism is the view that the past and present exist but the future does not. We can also label some views on the second question. The A-theory answers in the affirmative: the flow of time and division of events into past (before now), present (now) and future (after now) are objective features of reality (as opposed to mere features of our experience). Furthermore, they are linked: the objective flow of time arises from the movement, through time, of the objective now (from the past towards the future). The B-theory answers in the negative: while we certainly experience now as special, and time as flowing, the B-theory denies that what is going on here is that we are detecting objective features of reality in a way that corresponds transparently to how those features are in themselves. The flow of time and the now are not objective features of reality; they are merely features of our experience. By combining answers to our first and second questions we arrive at positions on the metaphysics of time such as: [ 26 ]

• the block universe view: eternalism + B-theory
• the moving spotlight view: eternalism + A-theory
• the presentist view: nowism + A-theory
• the growing block view: now-and-then-ism + A-theory.

So much for positions on time itself. Now for some views on temporal objects: objects that exist in (and, in general, change over) time. Three-dimensionalism is the view that persons, tables and other temporal objects are three-dimensional entities. On this view, what you see in the mirror is a whole person. [ 27 ] Tomorrow, when you look again, you will see the whole person again. On this view, persons and other temporal objects are wholly present at every time at which they exist. Four-dimensionalism is the view that persons, tables and other temporal objects are four-dimensional entities, extending through three dimensions of space and one dimension of time. On this view, what you see in the mirror is not a whole person: it is just a three-dimensional temporal part of a person. Tomorrow, when you look again, you will see a different such temporal part. Say that an object persists through time if it is around at some time and still around at a later time. Three- and four-dimensionalists agree that (some) objects persist, but they differ over how objects persist. According to three-dimensionalists, objects persist by enduring : an object persists from t 1 to t 2 by being wholly present at t 1 and t 2 and every instant in between. According to four-dimensionalists, objects persist by perduring : an object persists from t 1 to t 2 by having temporal parts at t 1 and t 2 and every instant in between. Perduring can be usefully compared with being extended in space: a road extends from Melbourne to Sydney not by being wholly located at every point in between, but by having a spatial part at every point in between.

It is natural to combine three-dimensionalism with presentism and four-dimensionalism with the block universe view—but other combinations of views are certainly possible.

Gödel (1949b [1990b]) argues from the possibility of time travel (more precisely, from the existence of solutions to the field equations of General Relativity in which there exist CTC’s) to the B-theory: that is, to the conclusion that there is no objective flow or passage of time and no objective now. Gödel begins by reviewing an argument from Special Relativity to the B-theory: because the notion of simultaneity becomes a relative one in Special Relativity, there is no room for the idea of an objective succession of “nows”. He then notes that this argument is disrupted in the context of General Relativity, because in models of the latter theory to date, the presence of matter does allow recovery of an objectively distinguished series of “nows”. Gödel then proposes a new model (Gödel 1949a [1990a]) in which no such recovery is possible. (This is the model that contains CTC’s.) Finally, he addresses the issue of how one can infer anything about the nonexistence of an objective flow of time in our universe from the existence of a merely possible universe in which there is no objectively distinguished series of “nows”. His main response is that while it would not be straightforwardly contradictory to suppose that the existence of an objective flow of time depends on the particular, contingent arrangement and motion of matter in the world, this would nevertheless be unsatisfactory. Responses to Gödel have been of two main kinds. Some have objected to the claim that there is no objective flow of time in his model universe (e.g. Savitt (2005); see also Savitt (1994)). Others have objected to the attempt to transfer conclusions about that model universe to our own universe (e.g. Earman (1995, 197–200); for a partial response to Earman see Belot (2005, §3.4)). [ 28 ]

Earlier we posed two questions:

Gödel’s argument is related to the second question. Let’s turn now to the first question. Godfrey-Smith (1980, 72) writes “The metaphysical picture which underlies time travel talk is that of the block universe [i.e. eternalism, in the terminology of the present entry], in which the world is conceived as extended in time as it is in space.” In his report on the Analysis problem to which Godfrey-Smith’s paper is a response, Harrison (1980, 67) replies that he would like an argument in support of this assertion. Here is an argument: [ 29 ]

A fundamental requirement for the possibility of time travel is the existence of the destination of the journey. That is, a journey into the past or the future would have to presuppose that the past or future were somehow real. (Grey, 1999, 56)

Dowe (2000, 442–5) responds that the destination does not have to exist at the time of departure: it only has to exist at the time of arrival—and this is quite compatible with non-eternalist views. And Keller and Nelson (2001, 338) argue that time travel is compatible with presentism:

There is four-dimensional [i.e. eternalist, in the terminology of the present entry] time-travel if the appropriate sorts of events occur at the appropriate sorts of times; events like people hopping into time-machines and disappearing, people reappearing with the right sorts of memories, and so on. But the presentist can have just the same patterns of events happening at just the same times. Or at least, it can be the case on the presentist model that the right sorts of events will happen, or did happen, or are happening, at the rights sorts of times. If it suffices for four-dimensionalist time-travel that Jennifer disappears in 2054 and appears in 1985 with the right sorts of memories, then why shouldn’t it suffice for presentist time-travel that Jennifer will disappear in 2054, and that she did appear in 1985 with the right sorts of memories?

Sider (2005) responds that there is still a problem reconciling presentism with time travel conceived in Lewis’s way: that conception of time travel requires that personal time is similar to external time—but presentists have trouble allowing this. Further contributions to the debate whether presentism—and other versions of the A-theory—are compatible with time travel include Monton (2003), Daniels (2012), Hall (2014) and Wasserman (2018) on the side of compatibility, and Miller (2005), Slater (2005), Miller (2008), Hales (2010) and Markosian (2020) on the side of incompatibility.

Leibniz’s Law says that if x = y (i.e. x and y are identical—one and the same entity) then x and y have exactly the same properties. There is a superficial conflict between this principle of logic and the fact that things change. If Bill is at one time thin and at another time not so—and yet it is the very same person both times—it looks as though the very same entity (Bill) both possesses and fails to possess the property of being thin. Three-dimensionalists and four-dimensionalists respond to this problem in different ways. According to the four-dimensionalist, what is thin is not Bill (who is a four-dimensional entity) but certain temporal parts of Bill; and what is not thin are other temporal parts of Bill. So there is no single entity that both possesses and fails to possess the property of being thin. Three-dimensionalists have several options. One is to deny that there are such properties as ‘thin’ (simpliciter): there are only temporally relativised properties such as ‘thin at time t ’. In that case, while Bill at t 1 and Bill at t 2 are the very same entity—Bill is wholly present at each time—there is no single property that this one entity both possesses and fails to possess: Bill possesses the property ‘thin at t 1 ’ and lacks the property ‘thin at t 2 ’. [ 30 ]

Now consider the case of a time traveller Ben who encounters his younger self at time t . Suppose that the younger self is thin and the older self not so. The four-dimensionalist can accommodate this scenario easily. Just as before, what we have are two different three-dimensional parts of the same four-dimensional entity, one of which possesses the property ‘thin’ and the other of which does not. The three-dimensionalist, however, faces a problem. Even if we relativise properties to times, we still get the contradiction that Ben possesses the property ‘thin at t ’ and also lacks that very same property. [ 31 ] There are several possible options for the three-dimensionalist here. One is to relativise properties not to external times but to personal times (Horwich, 1975, 434–5); another is to relativise properties to spatial locations as well as to times (or simply to spacetime points). Sider (2001, 101–6) criticises both options (and others besides), concluding that time travel is incompatible with three-dimensionalism. Markosian (2004) responds to Sider’s argument; [ 32 ] Miller (2006) also responds to Sider and argues for the compatibility of time travel and endurantism; Gilmore (2007) seeks to weaken the case against endurantism by constructing analogous arguments against perdurantism. Simon (2005) finds problems with Sider’s arguments, but presents different arguments for the same conclusion; Effingham and Robson (2007) and Benovsky (2011) also offer new arguments for this conclusion. For further discussion see Wasserman (2018) and Effingham (2020). [ 33 ]

We have seen arguments to the conclusions that time travel is impossible, improbable and inexplicable. Here’s an argument to the conclusion that backwards time travel simply will not occur. If backwards time travel is ever going to occur, we would already have seen the time travellers—but we have seen none such. [ 34 ] The argument is a weak one. [ 35 ] For a start, it is perhaps conceivable that time travellers have already visited the Earth [ 36 ] —but even granting that they have not, this is still compatible with the future actuality of backwards time travel. First, it may be that time travel is very expensive, difficult or dangerous—or for some other reason quite rare—and that by the time it is available, our present period of history is insufficiently high on the list of interesting destinations. Second, it may be—and indeed existing proposals in the physics literature have this feature—that backwards time travel works by creating a CTC that lies entirely in the future: in this case, backwards time travel becomes possible after the creation of the CTC, but travel to a time earlier than the time at which the CTC is created is not possible. [ 37 ]

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Mass IT outage: here's a list of companies and operations affected

• A huge global IT outage is disrupting flights, banks, retailers, and media outlets.
• The widespread disruptions have been linked to an issue with the cybersecurity firm CrowdStrike.
• Operations affected include airlines in the US and Europe, supermarkets, and some 911 lines.

A mass IT outage has hit flights, banks, retailers, and media outlets around the world.

The issues appear to be linked to the cybersecurity firm CrowdStrike .

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Delta and American had both canceled their ground stops by 7 a.m. ET.

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The major UK airports Heathrow, Gatwick, and Luton have reported issues, with some warning of delays and disruption.

Related stories

An X post from Gatwick Express , a train service for the airport, said the company was unable to access driver diagrams at certain locations, "leading to potential short-notice cancelations, particularly on the Thameslink and Great Northern networks."

A spokesperson for Belfast International Airport confirmed to BI that whiteboards were being used to handwrite flight information before systems were later restored. Whiteboards were also used at Singapore Changi Airport.

Hospitals and doctors' surgeries

Several hospitals and doctors' practices appear to have been affected by the outage.

In the UK, the NHS' EMIS system, which doctors use to book appointments, view patient notes, order prescriptions, and make referrals, appears to be having issues .

A spokesperson for the NHS told BI in a statement: "The NHS is aware of a global IT outage and an issue with EMIS, an appointment and patient record system, which is causing disruption in the majority of GP practices."

They said that long-standing measures were in place to manage disruption and that there was no known impact on 999 or emergency services, so people should use these services as normal.

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Two German hospitals canceled elective operations scheduled for Friday, Reuters reported.

NYCT Subway

Commuters in New York City and DC may also face delays Friday morning.

In an X post, the NYCT subway said: "Train arrival information is unavailable for A/B/C/D/E/F/G/J/M/N/Q/R/Z/Rockaway Park Shuttle/Franklin Av Shuttle due to a worldwide technical outage. Train service is unaffected."

The post said the tech outage also impacted Subway officials' ability to see train locations.

Broadcasters

Sky News also appears to have been hit by the outage. The UK news channel has been showing archive footage and briefly displaying an error message.

The news site appears to be up and running at the time of writing.

London Stock Exchange

The London Stock Exchange's website was also experiencing issues.

"RNS news service is currently experiencing a third-party global technical issue, preventing news from being published on www.londonstockexchange.com ," the company said in a statement.

"Technical teams are working to restore the service. Other services across the group, including London Stock Exchange, continue to operate as normal," it continued.

Retailers and fast-food giants

Bloomberg reported that McDonald's Japan suspended about a third of its stores in the country on Friday. The issue was with the stores' cash registers, the report said.

The grocery-store chain Woolworths told BI that some stores had "been impacted as a result of the global IT issue." All but six stores were open for business, but some had fewer functioning checkouts.

Delivery delays

FedEx and UPS are warning of delivery delays because of the outage.

In a statement on the company's website , FedEx said it was experiencing "substantial disruptions throughout our networks due to a global IT outage experienced by a third-party software vendor." The company said parcels due to be delivered on Friday might face delays.

A UPS spokesperson told BI that it continues to operate effectively but there may be some service delays due to third-party outage "impacting some UPS computer systems in the U.S. and Europe."

Some US state driver services are down

Drivers in some states are unable to access services because of the outage.

Georgia's Department of Driver Services posted on X that "due to the global Microsoft/Crowdstrike outage, DDS services are unavailable at this time."

Tennessee's Department of Safety and Homeland Security said some Driver Services Centers may not be able to process transactions, according to a post on X.

North Carolina's Department of Motor Vehicles driver license and plate agencies are also impacted and unable to assist customers, according to a CNN report.

Bloomberg reported that at the Ocean Park Marriott in Hong Kong, staff were using pen and paper to check guests in and said the outage was affecting their systems globally.

Marriott International later told CNN in a statement that "certain hotel systems" have been affected.

"We are actively working with our vendors to resolve issues that have impacted certain hotel systems," the company said in a statement to the publication. "We apologize for any inconvenience that guests may experience."

Watch: Global computer glitch grounds flights, knocks out 911

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The Time Travel Handbook

In the tradition of The Anti-Gravity Handbook and The Free-Energy Device Handbook, science and UFO author David Hatcher Childress takes us into the weird world of time travel and teleportation. Not just a whacked-out look at science fiction, this book is an authoritative chronicling of real-life time travel experiments, teleportation devices and more. The Time Travel Handbook takes the reader beyond the government experiments and deep into the uncharted territory of early time travelers such as Nikola Tesla and Guglielmo Marconi and their alleged time travel experiments, as well as the Wilson Brothers of EMI and their connection to the Philadelphia Experiment; the U.S. Navy's forays into invisibility, time travel, and teleportation. Childress looks into the claims of time traveling individuals, and investigates the unusual claim that the pyramids on Mars were built in the future and sent back in time. A highly visual, large format book, with patents, photos and schematics. Be the first on your block to build your own time travel device!

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