The Doctor's TARDIS is larger on the inside than on the outside. How can this be achieved?

The conventional answer is that

The TARDIS is dimensionally transcendental ... the interior exists in a different, relative dimension to the exterior.


However this seems to be gobbledygook. It's a lot of technical sounding words with no real scientific basis.

Note: I am not asking about the time-travel aspect - just how a container could be bigger on the inside than on the outside.


What real science could go some way to explaining how the Tardis can be bigger inside than out?

My main solution so far is.

The Tardis has a built-in portable wormhole. When you step inside, you have entered a real normal-size space in a different part of the universe. Maybe this space exists in a bunker on some planet. The problems are (a) how do you make a wormhole portable and (b) how would the Doctor cope if someone on the other planet attacked the bunker?

Can anyone come up with a better explanation? It needs to be based at least a little in real science. No magic is allowed or shrinking of atoms. As far as I know these aren't genuine scientific concepts.

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    $\begingroup$ A TARDIS isn't a genuine scientific concept, either. $\endgroup$ – Frostfyre Jul 13 '15 at 13:15
  • $\begingroup$ @Frostfyre - Thanks. However I'm not asking about time-travel in this particular question. I'm asking about making a container that is bigger on the inside than on the outside. I'll amend my question. $\endgroup$ – chasly from UK Jul 13 '15 at 13:27
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    $\begingroup$ wouldn't this question fit much better at scifi.stackexchange.com ? $\endgroup$ – bowlturner Jul 13 '15 at 13:41
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    $\begingroup$ @bowlturner It depends: if the question is, "how does the TARDIS work," then yes; but if the question is, "how do I explain something that is bigger on the inside," then it could be on-topic here. $\endgroup$ – 2012rcampion Jul 13 '15 at 13:43
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    $\begingroup$ "spacey wacey" springs to mind... $\endgroup$ – Scott Downey Jul 13 '15 at 13:48

The interior is a dimension onto itself. Basically it is a part of the same universe that has been seperated off through a scientific method (like a bubble inside another bubble) and then the equipment is "moved" into the new bubble via a "dimensional string" (never really explained in the shows or books, but guess its like a wormhole). Part of the equipment is obviously the space-time drive, but the majority is like a holodeck.

Why a holodeck? Because other than the needed equipment, people, and things brought in from the exterior real world, there are very few actual rooms within a TARDIS. The rest of the space is mathematically induced to allow for walls, doors, privacy, etc. In all likelihood a fractal-like formula is used, since this means that the pattern for a given wall can be repeated as many times as needed. As a direct result the "near infinite space" of the interior is limited not by power (in terms of energy) but in terms of "computing power". Rooms and objects can be added, saved, removed, deleted, or even jettisoned for thrust as either matter or energy. Rooms not used in a long time may be moved deeper into the ship or "saved" for long-term storage as data (personal objects should be kept in a primary room like the console room or workshop, as they may be degraded or lost if left in a random room and digitized for long-term storage).

Another misunderstood concept is that the TARDIS has more than one floor (cause it has stairs and elevators). All rooms are EXACTLY one-room tall, regardless of appearance. If you climbed stairs to the second floor in the console room and left the room, you would either return to the main floor of the console room, or find yourself in a different part of the ship. Stairs and elevators (when not clearly within a single larger room) appear to go up or down, but in reality they move you around vastly different areas of the ship. This is because of the fractal-like mathematics of the interior design (aside from furniture and the fixings like the color of bedsheets, every bedroom is identical to every other bedroom). As a result you could swear you are walking in circles, passing the same cargo bay, stairs, corridor, and intersection while at the same time swear that you have walked a perfectly straight line for a good quarter of a mile. (Sure, they re-use the same background sets for the effect, but that's how TV shows save money).
NOTE -- this may have changed with the new series, but the original conceptual framework that most older fans go by is that the ship has a fractal design, so "deeper" into the ship always meant "further from the exit/console room". NOTE 2 -- the other concept is that there is basically only one main multi-floor room, with the console room at the top and the engines and power storage and power transfer rooms underneath the console. Everything else appears flat but is actually on an unnoticeable slant running around this main tower-like structure ... Though it can still appear that you are walking in a straight line, you are actually walking down a ramp around a coil, similar to the thread on a screw. NOTE 3 -- the new season kind of refers to this as the "desktop theme". Since we know the interior is its own dimension, and it has more or less been described as a mathematically-induced dimension, and rooms can be moved/added/etc, all movement within the ship may simply be a matter of perspective. So you could walk a straight mile, swearing that you are somehow going in circles, and end up in a room three floors directly underneath the console room.

The "eye of harmony" (a captured blackhole) is mostly used to power the space-time drive, though a small amount of is power is converted into electro-static plasma or electricity or whatever the lights/computers/etc need. Originally the Eye of Harmony was hidden on Gallifrey and powered the various TARDISes through dimensional strings (meaning that a ship could be controlled remotely from Gallyfrey. You could override that control, but only to a limited degree. It was possible to completely cut that remote-control link, but it generally meant cutting off your main power supply too -- though you could also refuel at various time-rifts like the one in Torchwood's base in Cardiff, or find/install your own high-power energy source (meaning shorter trips with more frequent recharging stops. In the Peter Davidson 5th Doctor era the Master equipped his own TARDIS with its own power source in order to keep the Time Lords from tracking him via the power-link)

When the doors are closed, passage between the inside and outside becomes, for the most part, impossible. Often the TV show and books describe a police-box flying around, but that would really only apply in special circumstances. What you normally would see, if anything, would be a small probe-like device with various scanners/sensors (maybe the cube in the "flatline" episode is this device with all its vulnerable bits pulled in). Power is supplied to these sensors, and the data gathered, is transmitted via this "dimensional string". The "police box" is a hologram-like projection used to hide the real exterior which is even smaller (various sources quote it as a cold plasmic shell within a force-field, rendering it nearly impossible to damage), Each TARDIS can maintain several of these dimensional strings, with most of them being small energy/data types. When the ship lands/materializes, the tiny sensor-probe is instructed to "build up" a disguisable housing for the dimensional gateway/door.
Note - flying the ship with the doors closed but disguise (police box) materialized was considered risky at best and had potentially catastrophic risks involved. Never mind a bird flying in and pooping on the console, having the doors accessible meant there was the risk they might be forced open, and if the shields failed or were overloaded, one can imagine the damage a meteor could do if it hit the console.

In the event of instability of the interior dimension, an emergency door to a safe location would be created. However it was energy-expensive to form and maintain (farther from console room means deeper into the ship, making it more costly) so it would close as soon as any lifesigns in that part of the TARDIS were through it (to not only save power but to protect them from a possible explosion), and the door could lead anywhere in space/time (though generally "close to" the ship). (5th Doctor, Peter Davidson era, episode Terminus).

The "police box" disguise of the Doctor's TARDIS is, as described, "a flaw in the chameleon circuit". Older generations of TARDIS were basically limited to a phone-booth sized object to small rocket-ships, but always were the same thing -- an object with a hidden door. New generations (final ep of 2015, not the 2015 Xmas special) show that the exterior can now be very complex (is, a 1970's diner) with the door to the interior hidden as any object (freezer door, bathroom door, access door of a pop-can machine, etc) though objects and people in this complex exterior are left behind when it leaves (though a few fabric writers theorize that if you did a bit of technical trickery you could hop a ride this way, though it's not recommended as the air might also be left behind and you could be exposed to radiation or other such hazards such as the cold of deep space: though a local jump of a few minutes to the next county down the road might be survivable).

Smaller outside as better? This way the actual ship is quite tiny (think of gas mileage comparisons between a motorcycle, car, humvee, and a 747 are like. Travel in time is expensive, and getting from one galaxy to another in a few hours, no matter the method used, is expensive, so the smaller the ship can be made, the less power/fuel needed).


From the descriptions I've read it's something similar to this;

If you were to take a region of space-time and maintain a constant gravitational gradient, or at minimum, a 'natural' one - whilst 'throwing' the region down a gravity well - you would end up with what looks like a black hole on the outside but would be perfectly habitable on the inside. This artifact would need a power source capable of maintaining the structure of the warped space within it.

The space within isn't 'anywhere', it technically hasn't moved (note what has been described thus far is not a TARDIS nor is it capable of time travel - for that you need the in-universe 'time vortex').

It was best described (for me) as an ant walking up to a hole that is wider at the base than at the mouth, the ant can walk over the 'lip' and experience the signature "it's smaller on the outside" sense that the TARDIS gives it's passengers.


I grew up on DW and long before I learned anything significant about science, I came up with this rather childish, semi-scientific explanation...

When you put more than quart of water in a quart-size steel bottle, it works because the water compresses down smaller to fit. The water takes on different values in some of its characteristics, most notably in the rather nebulous trait called 'pressure'. It is still water and functions very much like it would outside of the bottle, its just smaller and a little heavier. Now imagine that you show your steel bottle to a very primitive scientist who does not yet know about pressure. He would think that the steel bottle is bigger on the inside than on the outside because that is the most intuitive explanation in the absence of the idea of pressure,

I don't know scientific history adequately to tell how long we have known about pressure, but I would guess that it is no more than a thousand years or so. If the Tardis creators are millions of years ahead of us in their exploration of science, I bet they know more than a few things which would confuse our intuition.

The greatest failing of Science in any age, is the tendency of its practitioners to believe that their current knowledge approximates all that can be known.

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    $\begingroup$ That is one strong quart bottle. To compress water by a factor of four you would need over 75,000 atmospheres of pressure. Don't know a more accurate number because the bulk modules (compressibility) of water is not constant. I am pretty sure the water would interpenetrate the steel at that pressure. Of course, the steel itself also undergoes compression, though water is about 70 times more compressible than steel. Hope it does not spring a leak. $\endgroup$ – Gary Walker Jul 23 '15 at 10:34
  • $\begingroup$ Thanks for the correction. I guess, even in my adulthood, I am not much of a scientist. I will change my example to a more realistic compression level. $\endgroup$ – Henry Taylor Jul 23 '15 at 14:27


Maybe Doctor Who shrinks when he enters the TARDIS? The inner space doesn't need to be bigger than the outer space if the objects that enter the TARDIS just shrink when they enter it and grow to their normal size when they leave the TARDIS.

  • $\begingroup$ But we have plenty of footage contradicting this. $\endgroup$ – o0'. Sep 12 '15 at 19:25
  • $\begingroup$ Sorry, I do not watch Doctor Who (yet). $\endgroup$ – MedwedianPresident2 Sep 12 '15 at 19:29
  • $\begingroup$ Not a problem, but still wrong ;) $\endgroup$ – o0'. Sep 12 '15 at 21:03

I would say it's a bit of independent space that's "glued" to ordinary space at the entry door. That also explains how time travelling works: That independent space is "unglued" from space, and then "glued" again to space at another time.

The rest of the police box is just a bit of camouflage in ordinary space to hide the glueing (because otherwise it would look quite strange; not to mention that accidentally walking into the glueing position from the side might turn out deadly because your body gets cut in half).

  • $\begingroup$ Interesting. Presumably the police box must be carried around in the independent space and then extruded into ordinary space when necessary. Otherwise the TARDIS would only be able to dock where there were police boxes. $\endgroup$ – chasly from UK Sep 12 '15 at 19:48
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    $\begingroup$ An alternative would be if the police box is a "holoprojection" similar to the Star Trek Holodeck objects. That is, it is a hologram combined with a sort of force field that makes it appear to be a solid object although it in reality isn't. IIRC the TARDIS could in principle show any form, and it is a defect of the Doctor's TARDIS that it always looks like a police box. A holographic projection would explain that ability. $\endgroup$ – celtschk Sep 12 '15 at 19:53

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