I used to think those are random events but someone over at physics.stackexchange.com insists that randomness means something else so I am at a loss here. Can someone help me out?

What do you call an event that happens without a cause?

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    spon·ta·ne·ous spänˈtānēəs/ adj. "performed or occurring as a result of a sudden inner impulse or inclination and without premeditation or external stimulus." "Happening or arising without apparent external cause; self-generated."
    – Kris
    Sep 12, 2013 at 13:21
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    Observer, it is more natural to ask questions like this with the wording "What do you call". Saying "How do you call" is unnatural and not really used by native speakers.
    – Tristan
    Sep 12, 2013 at 13:26
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    Does anything happen without a cause? Sep 12, 2013 at 15:55
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    Whether something can happen without a cause is an irrelevant philosphical question, and is not necessary to have in order to express the idea in language. Language has to be able to express imaginary ideas, hypotheses that are later refuted, fiction and of course plain old lies.
    – Kaz
    Sep 12, 2013 at 18:22
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    @RoaringFish Quantum mechanics
    – Izkata
    Sep 12, 2013 at 19:32

15 Answers 15


I would say a spontaneous event.

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    +1, but I can't vouch that physicists don't have some other meaning for "spontaneous" that they consider more important as well. Cranky lot.
    – T.E.D.
    Sep 12, 2013 at 13:54
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    @T.E.D. we certainly are, but I can't think of a technical meaning that would conflict. A quantum physicist on the other hand...
    – Chris H
    Sep 12, 2013 at 14:19
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    @T.E.D. Yeah. Grammar folk are never cranky.
    – mawcsco
    Sep 12, 2013 at 17:12
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    OK, I'll play the cranky scientist. Spontaneous means an event that can occur without a specific trigger, it does not mean that it has no cause. In a non-technical sense, I could spontaneously break into song but I would still have a reason for doing it. Presumably I would be very happy, or drunk or something.
    – terdon
    Sep 12, 2013 at 17:41
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    I remember spontaneous in chemistry as meaning the reaction would just happen when the two reactants came in contact. A non-spontaneous reaction would require an ignition or heat input. Baking soda and vinegar react spontaneously. A match igniting requires a trigger. Sep 12, 2013 at 19:06

It seems that the concept without cause is not a true criterion. Assuming we are not talking about supernatural events, there are physical, biological, social, political things that happened that contributed to the ultimate event.

The real sense behind the phrase is no known cause or no understood cause. I would therefore propose inexplicable

not capable of explanation; unexplainable

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    What you say may turn out to be true, but it's essentially a philosophical position. Linguistically, I think you could still assert that the word "causeless" has an underlying 'basic' meaning of "without cause" on some level -- even though, as you say, it might turn out that in real-world pragmatics that effectively boils down to "without known cause" or "without directly detectable cause" etc. Sep 12, 2013 at 14:36
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    @NeilCoffey The phrase without a cause can have numerous denotative and connotative meanings. Consider the film Rebel without a Cause. There are numerous indications of factors (causes) contributing to the characters' rebellion, but they all lack a commitment to a principle (a cause).
    – bib
    Sep 12, 2013 at 14:45
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    There are two sides to this: One is the disposition of said event and the other is the understanding of the event by the observer. To the extent that the Observer may not be able to explain the cause makes INEXPLICABLE a good choice. As to the root nature of the event however, the fact that the observer cannot explain the cause does not impact the facts around the cause itself. It could be argued that every event has a cause - it is only our lack of understanding that makes it INEXPLICABLE or believe it to be chaotic. Sep 12, 2013 at 18:28
  • Things may happen without a reason, but they never happen without a cause.
    – bill s
    Sep 13, 2013 at 4:49
  • @bib I agree, but that's of course not really the use of 'without cause' that I'm referring to. (Write it as a formal logic expression if it helps to avoid this kind of silly argument.) Sep 13, 2013 at 19:05

Well, there is always the word causeless: so you could simply say a causeless event. A rough synonym is fortuitous.

You could potentially say a random event or chance event.

The commentators on the physics forum are correct: as a scientific term, that isn't the technical meaning of random. But unless you're intending to use it as a technical term, so what? -- there are plenty of words that have a different everyday meaning to their technical meaning.

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    there are plenty of words that have a different everyday meaning to their technical meaning. That is unfortunately true, literally! Sep 12, 2013 at 18:52
  • "Fortuitous" gets my vote. Sep 12, 2013 at 20:56
  • Causeless makes a determination that the event had no cause (arguable) and does not consider that it was simply beyond the observer to understand it. Fortuitous as a primary definition may be appropriate but leans toward an event that was of good fortune (versus bad), which the OP did not imply. Nov 29, 2015 at 23:54

From OED...

acausal - not causal; independent of or not involving the relationship of cause and effect.

Here's an NGram showing how usage has increased during the Quantum era it fits so well with.

enter image description here

  • Looking it up in the OED is cheating :). Good find, +1.
    – terdon
    Sep 12, 2013 at 23:17
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    @terdon: I honestly couldn't say whether I actually remembered coming across it, or just took it for granted that it was bound exist (standard a- prefix meaning "without"). But I had OED open, and it was easier to get a definition there than fight Google telling me I probably meant to search for define causal Sep 12, 2013 at 23:53
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    Hmmm... I wonder if acausal events have actually increased since the Quantum era. ;-P
    – Simon East
    Sep 13, 2013 at 0:36

How about unprecipitated or unprompted?

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    Unprompted literally translates to French as impromptu, which, taken back into English, has a much closer meaning to "without a cause" than unprompted. Impromptu includes the concept of spontaneity, whereas unprompted simply means "without being encouraged or assisted to say or do something".
    – Kaz
    Sep 12, 2013 at 20:17

Random neither implies nor precludes a cause in itself. Causeless is an option: TFD: "having no justifying cause or reason"


A non-deterministic event. See http://en.wikipedia.org/wiki/Indeterminism.

Non-causal or acausal are also used in filter & systems theory.


An "act of God" is often used to denote an event that is out of anyone's control, and therefore "just happens". As a non-believer, I must confess a certain pleasure in describing "an event that happens without a cause" as an "act of God."

  • The French language root (and is used in many English legal papers) is "Force Majeure" and whilst providing a very vague definition, hearkens to the days when, lacking facts, people believed the Earth was flat, our Sun revolved around the Earth, etc. There are probably better answers here to describe the case of an observer who does not understand the cause behind an event versus accepting that events are without cause or that the Earth is flat - conditions that simply punctuate our lack of understanding of the situation. Nov 30, 2015 at 0:01

Yes random events are not necessarily causeless. I can think of a few words:




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    It's easily understood, but I must admit I've never come across unincited before. The spellchecker in my Google Chrome browser doesn't recognise it, and it "flatlines" in NGrams by comparison with unprovoked (and even by comparison with the latest technical buzzword "acausal"). Sep 12, 2013 at 21:11
  • How about unsolicited?
    – Jim L.
    Sep 13, 2013 at 3:21
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    Unincited is simply morphology at work: un plus a word. Not every possible English word is in dictionaries or in wide use, just like not every possible English sentence has been written down and cataloged as part of the language. Of course dictionaries do not list every possible "un" word; it is space-wasting and counterproductive to do so. Also, it's just a quirk of orthography that "un" is written without a space from the word that follows. What if the rules for writing were such that it was written "un incited"? Then of course, both words would be in your dictionary, and that is that.
    – Kaz
    Sep 13, 2013 at 5:36

For a more literary word choice, you could also consider deus ex machina to explain things without apparent, erm, explanation.

Latin for "God from the machine", it's a plot cliche first lamented by Horace way back in the day. As the translation implies, it used to literally mean having a god (usually Zeus) descend down at the climax of a play or story to conveniently intervene and solve whatever problems were being presented.

Today the term is usually used to describe media where an event happens seemingly out of the blue. For example, the Naval officer passing by at the end of William Golding's The Lord of The Flies who rescues the boys, or the various machinations of Douglas Adams's Infinite Improbability Drive.

In any case, an event with no obvious cause, especially one which thwarts expectations or otherwise introduces chaos, is by definition a deus ex machina, since any explanation you ascribe to it is as good as the next.

  • The problem is that deus ex machina cannot be easily disentangled of its connotations of "cheesy plot twist" so that it can be used to simply denote a causeless event.
    – Kaz
    Sep 12, 2013 at 20:20
  • I agree completely, I think deus ex machina requires a certain context and connotation, I just like options when I'm picking words to describe things.
    – Kyle Hale
    Sep 13, 2013 at 13:38

Depending on context also consider self-generated

self-generated adjective 1. happening or arising without apparent external cause; "spontaneous laughter"; "spontaneous combustion"; "a spontaneous abortion" [syn: spontaneous] [ant: induced] 2. originating from the self

Another apt word is unengendered from


etymology engender (v.) Look up engender at Dictionary.com early 14c., "beget, procreate," from Old French engendrer (12c.) "engender, beget, bear; cause, bring about," from Latin ingenerare "to implant, engender, produce," from in- "in" (see in- (2)) + generare "beget, create" (see generation). Meaning "cause, produce" is mid-14c. Related: Engendered; engendering.

Other alternatives along similar etymological lines are



giving the sense of having no beginning or cause (self-existent).

en·gen·der verb \in-ˈjen-dər, en-\ : to be the source or cause of (something)



a spontaneous event is an event that happens spontaneously like a spring not with out a cause necessarily


The word I have most seen in this context is, quite simply, uncaused.


Idiopathic seems like the right choice.


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    Idiopathic is just a fancy word we use in the biological sciences to mean I dunno why. It is used to indicate, for example, that the cause of a patient's illness is something specific to that patient, not that there is no cause.
    – terdon
    Sep 12, 2013 at 17:46
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    And doesn't the suffix pathic imply pathological? Sep 12, 2013 at 21:03

an event without cause, should be the first event of history. it's called God, according to Assisi AFAIK.

To speak to a wider audience without rejection (on religious grounds), you may call this a "god-event" ala the so-called 'god-particle'

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    This assumes that there is a primary event, and secondly that there is only one. If there can be multiple primary events, then time effectively has multiple independent starting points.
    – Kaz
    Sep 12, 2013 at 20:35
  • @NewAlexandria: Yeah, nice edit. sincerely.
    – SDReyes
    Sep 12, 2013 at 21:21

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