At the start of Back to the Future there is an exchange between Doc Brown (on the phone) and Marty, who is in Doc's lab, during which all of Doctor Brown's clocks start to chime. Doc Brown explains that he had had done an experiment which set all of his clocks 25 minutes behind.

Doc: Are those my clocks I hear?
Marty: Yeah, it's 8:00.
Doc: They're late. My experiment worked. They're all exactly twenty-five minutes slow.
Marty: Wait a minute. Wait a minute, Doc. Are you telling me that it's 8:25?
Doc: Precisely.

Is there any evidence in or out of universe for what experiment Doc Brown had performed which set all of his clocks behind by twenty-five minutes?

  • 23
    He was building a working time machine... seems like an experiment was with changing time. – DVK-on-Ahch-To May 20 '14 at 1:03
  • 4
    My personal theory is that each clock ran at a different speed (it took some 59 minutes to run an hour, some 61 minutes, etc.) All of the clocks individual "phases" synchronized at 8:25 am. – Jim Green May 20 '14 at 17:48
  • 1
    Localized time warp field? – user16696 Jun 13 '15 at 2:28
  • So there's one method some people use it to set your alarm clock to this time you want to actually get up or leave to go smile. So assuming if doc Brown had AD(H)D found the method of setting the clocks to the wrong time to trick the brain a sense of urgency. Some people with ADHD ADD would use this method. OR Doc Brown accidently traveled around 25-35 minutes and ended up not realizing it but saw all good clocks on the wrong time and being so fixated on time he hyper focused on resetting all the clocks to "the correct time" But realized later that he was wrong and was hyper focused on the DeL – Mr. Randall Oct 3 '20 at 23:18

It is one of the many things in the opening sequence of the movie that point to the fact that Doc Brown is...eccentric, to say the least. He leaves all the machines in his lab running, including his wake-up-and-make-breakfast machine, for several days. He leaves a speaker hooked up to his electrical equipment in such a way that it creates so much feedback as to blow out the speakers and send Marty flying into the wall.

And, somehow, he set his clocks, all of them, to go off exactly 25 minutes slow despite not having been there for days if his other equipment is any indication.

Now let's consider that past bit of information - somehow, he managed to set his clocks back 25 minutes, all of them, without having checked on any of his equipment in the past several days. What kind of event could cause such a discrepency in time?

Time Travel.

Doc Brown has been experimenting with his time machine. In fact, I think it's safe to say that his experiment with Marty is not the first time travelling experiment he has undergone - it's distinctly possible that he's run some small-scale tests with lower-wattage devices, and the state of his lab is the result of these experiments.

This, however, is all speculation - his lab's status could be the result of some other experiments. Remember, when Marty meets Doc Brown in the past, he's been experimenting with a mind-reading device. The time machine is the first one that really worked out the way he had hoped. It's not unreasonable to assume he's been doing a lot of other experiments as well.

So in short, there's two possibilities:

  1. It's all part of his experiments in time travel.
  2. It's part of some other experiment we aren't privy to, due to coming in during the middle of it as Marty does.
  • The breakfast machine is an example of a Rube Goldberg machine by the way – Zommuter Oct 29 '15 at 19:55
  • 3
    Why couldn't they have been 25 minutes slow days ago? – OrangeDog Jul 3 '16 at 18:28
  • @OrangeDog They could have been, but this wouldn't invalidate either theory - we don't know how long he's been experimenting on time travel, nor how long his other experiments have been going on. Nor do we know when Marty last came by for a visit. All we know is that Doc Brown's lab is in a state of disarray, and when Doc Brown hears all the clocks go off at once, he gets very excited - he specifically says "it worked!" as if some experiment has been a success, and the clocks going off at that exact time were proof of it. – Zibbobz Jul 5 '16 at 12:52
  • 1
    @KlaymenDK Nope - Marty may have connected his guitar to the setup, but when Doc Brown calls and Marty complains about the equipment being left in disarray, Doc explicitly tells Marty that there could be very dramatic feedback from hooking up to the amp. So, it's entirely Doc's fault and he knew it would happen. – Zibbobz Apr 11 '18 at 13:22
  • 1
    ...aaand I've just realised this is an old answer! Dunno why this was bumped in my feed? Well, a +1 is a +1!! – Kwola-T Jun 27 '18 at 19:32

When he calls to his lab, we are certain he already has a complete time Delorean ready.( "Could you meet me at Twin Pines Mall at 1:00AM? I made a major breakthrough..." )This before he gets all excited about all the clocks being 25mins slow, so, we can deduce this is unrelated to any kind of R&D or testing for the time Delorean.

The clocks are different, some are AC powered, some on batteries some old windups, enough to prove he sent that whole damn building 25mins into the future. Presumably without it moving 88MPH horizontally. Its showing that Doc had other ways of time traveling from the start, aside from his Delorean.

  • 7
    This could be quite a good answer if you edited it with a chainsaw and added some paragraphs. – Valorum Aug 15 '14 at 8:42
  • Why assume he sent the whole building into the future, as opposed to just gathering the clocks and stuffing them into the DeLorean? – Hypnosifl Jun 19 '15 at 3:49
  • 2
    @Hypnosifl This was my thought. At the mall, he calls Einstein the first time traveler, but never said it was the DeLorean's first trip through time. – Michael Itzoe Jun 19 '15 at 14:25
  • 3
    @Michael Itzoe - A point against this theory is that when Doc was talking into the video camera before sending Einstein through time, he said. "this is temporal experiment number one". Maybe you could imagine it was just the first formal experiment he named, but that comment combined with his excitement over the "temporal displacement" kind of suggests that previous time jumps would go against the spirit of the scene. Maybe his earlier experiment was something as simple as a universal remote for all his clocks that could offset all their readings by the same amount when he wasn't home! – Hypnosifl Jun 19 '15 at 16:00

I think Doc went back in time first, an staged all of this to teach Marty a lesson an so he would not make the mistakes in his future. He set the clock in the beginning of the first movie, back 25 minutes and then went a few days back in the future. Made the call an confirmed he had went Back in Time. What do you think? The reason he had him record it an had the Einstein go first was to show Marty how it worked. That's why he had the letter an vest at end. An told him he would draw there fire. Why not get in time machine? He was never dead. Well part of my theory is in the the above exsplination. But when doc goes to get more plutonium it looks like 2 have been used. The first one. An one on bottom row.

  • 1
    Do you have any evidence to support this theory? – Often Right Jun 13 '15 at 1:56

I always thought they were his control group and that he set them 25 min slow. Every other clock (except the tower ;) would show 8:25. But I'm not sure why you'd want to, other than setting up a plot coupon that later helps us understand why Einstein's watch is one minute fast.

Doc: They're [all set] late. [By the way] My experiment worked. They're all [still set] exactly twenty-five minutes slow [just like my watch, that was set 25 minutes slow; sent through time for 25 minutes, and now shows 8:00, unlike your watch, you slacker].


The obvious answer is that because Marty had been to 1955, Doc Brown already had knowledge of dates and times for when the original time displacement needed to happen due to the fact that he had seen the entire video back in his lab in 1955. The entire movie gives clues to this, Marty's watch constantly not telling the correct time, Doc's clocks being 25 minutes slow... Doc set everything up so that he would make sure Marty was right on time so everything would go off without a hitch. I'm surprised nobody caught this. Another example would be him encouraging Goldie Wilson to be mayor. The only things that blows a hole in my theory is the fact that the mall changes name after he destroys one of the "twin pines" and you could also reference the name change of the ravine in the 3rd instalment.

  • Wait so why were they slow? Could you edit to make your answer a bit clearer? – Edlothiad Jun 27 '18 at 8:52
  • A nice theory, but like you point out the present (1985) isn't changed until after Marty goes back in time. The mall sign, Marty's family, Biff, the 4x4 truck, and Doc. – Xantec Jun 27 '18 at 10:41

Another hypothesis (not really an answer because I can't show a specific experiment):

The clocks were never 25 minutes slow - Doc's watch/clock on the other end of the phone line was 25 minutes fast.

(I like this hypothesis better than my previous one, but I guess I'll leave the other there just in case it helps someone else find a better explanation)

Supporting research for Doc's watch being 25 minutes fast

Doc said the clocks were "exactly 25 minutes slow", but we don't know what he was comparing them to. They could have been slow relative to a watch that he had been experimenting on. So, a more accurate statement may have been that the watch he was comparing the clocks to was 25 minutes fast (because it came from the future maybe?). But, Marty hangs up on him to rush off to school before Doc could have potentially explained that.

This theory is backed up by a later suggestion in the film that experiments have been done on Doc's watch(es) that make other clocks/watches appear to be running slow. Primarily when Marty first starts recording Doc before they put Einstein in the time machine. Doc time stamps the recording as 1:18 AM and Marty seems puzzled and thinks maybe his watch has stopped (which he awkwardly holds to his ear as if he could hear a digital watch tick). This suggests that Doc's watches are ahead of the time Marty expects them to be making Marty think his watch had stopped.

However, I don't think the time discrepancy observed by Marty at the mall is the same 25 minute discrepancy he observed at the beginning of the movie. In order for Doc's watch to have been 25 minutes ahead when it was reading 1:18 AM, Marty's watch (and presumably the mall sign) would have needed to read something along the lines of 12:53 AM. But, we know the mall sign said 1:16 before Marty started on his way to the van.

Marty didn't compare his watch to the mall sign that we saw though. So, at the point Marty was at the mall sign either:

1) Doc's previous experiment(s) affected the mall sign in addition to his stopwatches (allowing them all to potentially be 25 minutes ahead), but not Marty's watch - and Marty didn't notice (or at least wasn't shown noticing) the sign was 25 minutes off from his own watch


2) Marty's watch and the mall sign were both set to 1:16 (makes sense because Doc asked Marty to be there at 1:15) and Doc's watches were at 1:17-ish (stopwatches can't be 25 minutes ahead because they read 1:19 a couple of minutes later in the film)

While I do like the simplicity of there being only one previous experiment making a single 25 minute discrepancy (which fits with the one missing container of plutonium that @user46913 pointed out in his answer), option 2 sounds more likely to me than Doc's experiment affecting the mall sign. So, I like to think Marty's watch said 1:17 when Doc said his watch was 1:18. This is also somewhat solidified by Doc only sending Einstein one minute into the future (ie. maybe that's what he did in his most recent experiment with his watches also).

This doesn't allow for much time to pass between Marty being at the mall sign at 1:16 and filming Doc at 1:17, but this is Hollywood. They put 4+ minutes of film between the two clips of the stop watches that showed only 3 minutes had passed. So, I don't consider one minute of Marty/Doc's story being told using a little more than a minute of film to be too much of a stretch for the usual Hollywood time distortion.

And, I say Doc did experiments directly on his watch(es) rather than experiments on himself or Einstein that affected the watches because Doc does explicitly say that "Einstein has just become the worlds first time traveler" after he sends him a minute into the future. So, I doubt Doc sent himself or any other living thing worthy of the title "time traveler" before then. But, he left the possibility for experiments on other non-living things - ie just experimenting on clocks/watches.

Lack of evidence for clocks being 25 minutes slow

The only reference outside of Marty and Doc's conversation about the clocks in his workshop being slow was when Marty was explaining his reasons for being late to school to his girlfriend. But, this is questionable because Marty is apparently always late for school (late four times in a row according to his girlfriend and the school principal). Which means he could have been late even without clocks being slow. But, before his girlfriend could comment on his statement about Doc setting the clocks 25 minutes slow, the principal interrupted them. Perhaps she was about to say, "But Marty, you're only 2 minutes late." I guess we'll never know. :)

The only time pieces outside of Doc's workshop that could have backed up this explanation are the watch on Marty's wrist, and a clock outside a business when Marty is hanging off the jeep on the way to school. Unfortunately neither are in focus enough to see the time. You can almost see the time on the clock in town, but we don't know how long the ride was from Doc's workshop to the clock outside of the business anyway.

  • 2
    I think your "Lack of Evidence" argument is stronger than you give it credit for. The fact that he told Doc that he was late for school immediately upon finding out that the clocks were running slow is a very strong argument that the clocks were actually slow and not related to Doc's watch being fast. – psubsee2003 Jul 3 '16 at 0:07
  • 1
    Your argument would be believable if his "I'm late for school" statement didn't happen immediately after learning the clocks were "slow". Yes, he may have a habit of being habitually late, but I don't see why he would react like he did if he thought he wasn't on-time. – psubsee2003 Jul 3 '16 at 0:14
  • 1
    They never showed us that he ever looked at the watch on his wrist during the phone conversation with Doc. He even asked Doc, "Are you telling me that it's 8:25?" despite there being a watch on his wrist. When Doc replies then Marty says "I'm late for school." So, his statement was still based on what Doc said as far as I can tell and is not evidence for anything other than there being a time difference between whatever time piece Doc was looking at on the other end of the phone and the clocks in Doc's workshop. – David Woodward Jul 3 '16 at 0:20

I've formed my own hypothesis that Doc Brown was doing a small side experiment to test the theory of parallel realities with time travel. (ie. the theory you can go back and kill your great grandfather without erasing your own existence because the reality you went back to is different than the reality you came from)

So, for example, maybe he decided to make sure he wasn't at home for a specific period of time (hence the piled up dog food and such) so that he could come back from another timeline (potentially another reality) and set his clocks back 25 minutes without fear of running into himself. If he found that his clocks were suddenly 25 minutes slow upon returning home (or when Marty came by in this case) then he knew he was able to affect his own reality/timeline by traveling forward/backwards in time. That would prove that the reality you originate from and the destination reality are one in the same (ie. don't kill your grandfather because then you're dead).

Setting the clocks would be a subtle way of proving this without tipping his hand to his past self about future events as might be done if he used notes on futuristic paper or with odd hand writing due to an injured finger that hadn't happened yet, etc.

Note that he could have come back and set the clocks from any point in the future. In other words, it was indeed "temporal experiment number one" that Marty saw with Einstein, because it was some future time travel experiment (between say part 1 and 2) that Doc Brown went back and set the clocks back 25 minutes as a message to himself.

This also allows for him to surprise himself by having set the clocks back before he knew time travel was possible (because as of experiment #1 he couldn't know with any certainty about experiment #5 where he went back and changed the clocks). And, he still didn't know if his experiment at 1:00am was going to work because he didn't know what point in the future he came from to set the clocks. It could have been some experiment a month away.

Why so many clocks? I dunno. Because he's a little nuts I guess. :)

  • 1
    Do you have any evidence to support this fan-theory? – Valorum Jul 2 '16 at 11:34
  • Sorry for wasting your time @Valorum. I have not one single shred of evidence - unless you count the piled up dog food. As Zibbobz said in his popular answer, "This is all speculation.". That's why my first sentence says it's a hypothesis. I just wanted to throw it out there as a starting point for further investigation in case some else has more time than myself to go digging into the matter. – David Woodward Jul 2 '16 at 17:21
  • TBH I have much the same problem with his answer as I do with this one. Fan-theories are fun, but without any justification, they're just pure guesswork. – Valorum Jul 2 '16 at 17:23
  • 2
    I'll remove my answer if I see any "evidence" or something other than "fun fan-theories" posted as answers here. Until then I think my answer offers just as much as the rest of them. Or a mod can take it down - whatever. I'm not exactly invested in this community. I doubt I ever will be if "fun fan-theories" get down voted. Without that "fun" it seems like the forum is just a bunch of people offering references to video/audio time stamps and book page/paragraph numbers for "evidence" - sounds like court case research. The fun discussions are part of the appeal of fictional works for me. – David Woodward Jul 2 '16 at 18:36
  • 1
    The purpose of SE is to provide answers that are definitive. That (generally) means evidence-driven. While it's perfectly acceptable to post an answer based on guesswork, it needs to be informed guesswork. – Valorum Jul 2 '16 at 18:38

Not the answer you're looking for? Browse other questions tagged or ask your own question.