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This question I have is similar to How much does the Doctor's TARDIS weigh from the outside? but different because I am wondering what its true weight is.

Is there anything in Doctor Who that hints at what the TARDIS' true weight is? In the most recent episode "Flatline", The Doctor states that if The TARDIS landed on Earth with its true weight it would fracture it.

  • The best we can use as a guess is the "dead" TARDISs in The Doctor's Wife, but even then we have to assume that those are the TARDIS's true shape, and that they are the same model TARDIS, and even then we can only estimate a weight based on visible size. Basically, this is unanswerable. – Lightness Races in Orbit Oct 22 '14 at 17:03
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    Nitpick, but no doubt you mean "mass". Its weight is what it appears to be. – Daniel Roseman Oct 22 '14 at 17:08
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    @DanielRoseman: Not really. Knowing its mass is the same as knowing its weight, assuming we state the gravitational field in which the weight is measured (e.g. Earth gravity). Still, yes, calling it "mass" makes more sense in general for a spacecraft. – Lightness Races in Orbit Oct 22 '14 at 17:13
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    Anyway the real question might be 'how much of the Tardis' actually exists in our universe, and not some pocket universe, that is outside? You possibly need to think of the Tardis as a door. You are basically asking what is the weight of the door, but that door might contain an entirely separate universe. – Zoredache Oct 22 '14 at 18:02
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    A lady never tells. – Paul D. Waite Oct 22 '14 at 20:17
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Conceptually the TARDIS does not have crazy mass in our Universe because most of it ISN'T IN OUR UNIVERSE. We have seen the TARDIS carried off multiple times, in something small as a flatbed truck.

In Flatline, when the TARDIS was losing "dimensional energy" the outer representation (and that is all the shell of the TARDIS is; a representation of a portal to the smaller pocket dimension/universe within) the TARDIS lost dimensions and grew smaller. It was still portable and able to be carried around in Clara's purse. Nor did it appear to lose any of its internal dimensional spaces as it has in previous episodes.

  • We know the TARDIS does not exist completely within our Universe. It is a vast but finite pocket dimension/universe that intersects at the doorway to the TARDIS. This doorway is an interface or bridge between the pocket universe of the TARDIS and the Universe of 11 dimensions we exist in.

From Wikipedia's TARDIS Entry:

  • Apart from the ability to travel in space and time (and, on occasion, to other dimensions), the most remarkable characteristic of a TARDIS is that its interior is much larger than it appears from the outside. The explanation is that a TARDIS is "dimensionally transcendental", meaning that its exterior and interior exist in separate dimensions.
  • In The Robots of Death (1977), the Fourth Doctor tried to explain this to his companion Leela, using the analogy of how a larger cube can appear to be able to fit inside a smaller one if the larger cube is farther away, yet immediately accessible at the same time (see Tesseract).

  • According to the Doctor, transdimensional engineering was "a key Time Lord discovery". To those unfamiliar with this aspect of a TARDIS, stepping inside the ship for the first time usually results in a reaction of shocked disbelief as they see the interior dimensions ("It's bigger on the inside!").

Given what we know about just one room on the TARDIS makes the weight of the TARDIS vast, but calculable, if it were able to materialize completely within our Universe.

The Eye of Harmony Chamber

The chamber housing the Eye of Harmony has had multiple representations and they have varied wildly in the different versions of the series, but the one thing remains true. No matter its size, it produces chronal energy allowing the TARDIS the capacity to travel through time.

  • The Eye of Harmony is a star on the verge of collapsing into a Black Hole. It is this state of collapse which allows the TARDIS to harness the energy necessary to travel through time. This star is held within a sliver of Time so that it can be harness for its chronal energy as the star collapses.

  • While this collapsing star is not equal in size or power to the original Eye of Harmony in scope or scale (the original Eye of Harmony was said to power remotely all active TARDIS being used by the Gallifreyans as long as they remained in our Universe) it is still a star massive enough to be collapsing into a black hole. This means it is a star whose mass is two and a half to ten times greater than our sun because only stars with that kind of mass can BECOME black holes at all!

  • Should the TARDIS actually manifest completely within our Universe, the mass of a star held in collapse would also be part of that mass. Note that even in siege mode where the TARDIS is running out of energy, it grew smaller, closing the aperture between our Universe and its pocket dimension in the recent Flatline episode.

Given the Doctor's First Rule: The Doctor Lies...

While the Doctor said the weight of the TARDIS would fracture the Earth, I think he was underestimating it so that he wouldn't alarm Clara. Clara is a clever girl and probably suspects the true nature of the TARDIS already, but like most Humans, vast numbers and galactic scales simply don't truly make sense to our mortal minds.

  • Note the size of the TARDIS as it collapses into Siege Mode. The portal grew smaller and I suspect if the TARDIS continued to lose dimensional energy, the portal would eventually shrink out of existence protecting anything, say, like a planet in our Universe from the terrible mass of a suddenly completely materialized TARDIS.

  • From what I have read in the novelizations of the TARDIS, when we see the Doctor in the episode near the end of his life, the giant-sized TARDIS while appearing ancient is still utilizing its powers to maintain its existence in our Universe. This was not an accident. My suspicion is the TARDIS was trying to rescue the Doctor even as he and it lay dying.

    • From the novelizations when a TARDIS is lamenting its bonded partner, they often commit suicide by throwing themselves into a star. Or materialize onto a planet destroying it (we assume the planet would be empty...)

In summary

Given what we know of the internal dimensional shifting and manipulations of space within the TARDIS:

  • Its mass is not infinite, if it was, it would be greater than the Universe and thus unusual given there were thousands of TARDIS in existence at any one time. Since they were created outside of our Universe and then brought into it, it would seem likely they are not infinite in size.

  • But if we assume a finite mass, existing albeit in a pocket universe, as a reasonable assumption and given we know the mass of at least part of the TARDIS, we can safely assume the TARDIS must have at least THAT much mass if not more.

  • The mass of a single supergiant star (necessary to create a black hole and power the Eye of Harmony within the TARDIS) would indeed be sufficient to fracture and ultimately destroy all life on Earth should the TARDIS' inner pocket Universe suddenly coincide with our own.

  • Is there a canonical reference to this idea of the TARDIS being a door to a pocket universe, or being created outside the universe? From my recollection as a lifelong fan, all we really know is that it's bigger on the inside, and that this is achieved with Timelord technology. It's also not at all clear that the Eye of Harmony is located in the TARDIS. It was depicted that way in the 1996 movie, but all references before and since put it on Gallifrey AFAIK. – Nathaniel Oct 23 '14 at 10:17
  • @Nathaniel - they're not usually considered canonical, but are at least sometimes used as a source by the producers these days, but I'm pretty sure some of the Big Finish audio plays refer to the TARDIS interior as being inside a pocket universe. The Eye of Harmony was also depicted as being inside the TARDIS in the episode "Journey to the Centre of the TARDIS" in the 2012/2013 season. – Periata Breatta Oct 27 '14 at 12:41
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In series 7 "Journey to the centre of the TARDIS" the Eleventh Doctor stated:

Picture the biggest ship you've ever seen...and now forget it, because this ship is infinite.

It even has a suspended star as a power source, according to this same episode, so my guess is that the Twelfth Doctor actually fell short in his statement: if the TARDIS landed on Earth with its true weight, it might probably destroy it...and the solar system along with it.

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    This was hyperbole, not a statement of mathematical fact. – Lightness Races in Orbit Oct 22 '14 at 17:01
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    Rule #1 is that the Doctor lies. Even Timelord science can't make something infinite. – Valorum Oct 22 '14 at 17:36
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    +1, because although the Doctor's statement can't be taken literally (The TARDIS is finite at any point in time, but it's potential growth is unbounded), I still think infinite mass is the most correct answer. The mass of the TARDIS at any one instant is the mass of all the rooms put together. But in general? The best answer to me is the average mass, which is pretty obviously infinite – Jason Baker Oct 22 '14 at 18:10
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    @JasonBaker I think infinite mass is most correct in the sense that there is no limit to the masses that can be added to what's inside it. On the other hand, I don't follow what it would mean for an average mass to be said to be infinite. I've even seen it spin and get bounced about fairly easily, in earlier episodes (4th Doctor). – Dronz Oct 22 '14 at 19:05
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    @JasonBaker That's a fun video, but it's as much about logic and philosophy and language as it is about physics. Really, "immovable object", "unstoppable force" and "infinite mass" are all undefined, non-existent (to our knowledge), contradictory, inconsistent with physics, and so don't really have frames of reference that make sense without invoking some new way of thinking which generally hasn't been thought out by non-actual-Time-Lords and requires bending or breaking other things to allow it to exist. Which ya, is probably what the TARDIS does. ;-> – Dronz Oct 22 '14 at 21:30
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In the name of the Doctor, we get a pretty good idea of the true size of the TARDIS. With all of the dimensional shifting capabilities winding down, it appears to be around 5-700 feet high.

Assuming that 80-90% of this is empty space (and ignoring the fact that it appears to contain its own black hole), then the weight is presumably about the same as a building of a comparable size, something around 200-300,000 tonnes and certainly sufficient to "fracture the surface of the Earth" if it landed.

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In the episode "Full Circle", Lady Romana pegs the weight at around 5000 tons but this may simply be the current weight (in some sort of "don't move me" mode) rather than the TARDIS' true weight

ROMANA: Adric, is there any machinery on your planet that could lift the Tardis?

ADRIC: How heavy is it?

ROMANA: Er, five times ten to the six kilos in your gravity.

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    The exterior of the TARDIS was growing but we have no way of knowing whether this was the true height. Indeed, it's still got its false shape on! – Lightness Races in Orbit Oct 22 '14 at 17:02
  • @LightnessRacesinOrbit - That's true. There doesn't appear to be any recent cracking in the vicinity of the base though. – Valorum Oct 22 '14 at 17:34
  • I don't follow. Cracking? – Lightness Races in Orbit Oct 22 '14 at 17:35
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    What ground would be displaced? The TARDIS is resting on the ground, not embedded within it. At best you might expect some bunching up of grass and dirt and little stones and stuff, but even that can be weathered away pretty easily. – Lightness Races in Orbit Oct 22 '14 at 17:39
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    Nitpick: Kilograms are always kilograms in any gravity. It is a mass unit. – Zan Lynx Oct 23 '14 at 23:39
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My interpretation has always been that the Tardis is of infinite size and, therefore, infinite weight. Also, the Eye of Harmony is a black hole, so the Tardis should weigh as least as much as a black hole, if not more.

  • The TARDIS doesn't actually have the Eye of Harmony though. – DoctorWho22 Oct 22 '14 at 16:34
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    It doesn't? checks wiki Says on the Tardis wiki that the tardis the Doctor has includes a "mathematically modeled duplicate of the Eye of Harmony". Whatever that means. Source: tardis.wikia.com/wiki/… – chif-ii Oct 22 '14 at 16:38
  • "Infinite size" is absurd, as is "infinite weight". – Lightness Races in Orbit Oct 22 '14 at 17:01
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    @LightnessRacesinOrbit Welcome to Doctor Who. For reference: in the serial Logopolis, it's revealed that the heat death of the universe is averted by a bunch of old guys speaking mathematical formulae out loud. – evilsoup Oct 22 '14 at 17:20
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    @LightnessRacesinOrbit That sounds like a challenge :v – evilsoup Oct 22 '14 at 17:22
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The Weight of the TARDIS as mentioned by Susan in the Hartnell Era is approx. 68,000 Tons, however this may have just been based on the default interior Deadweight tonnage at the time, which in DWT only measures the rooms and people and cargo.. On the flip side tho, a TARDIS dimensional Transcendentalism is accomplished by the Relative Dimensional Stablisers which are separated into scales via Dimensional Field barriers. so while the core section for the ship is in a 1:1 relative scale with the normal universe, the RDS system can shrink a person, per each level of Dimensional Field Barrier (Dimension Dam for short) and would allow the scale factors to be smaller but the rooms relatively large or normal scale in those reduced scale factors lesser then 1:1 factor. now, in the case of the Eye of harmony, it's mass is held in stasis under the time factor, so while it is suspended in animation, inside the TARDIS the time that exists is given, but since the eye of harmony copy is a non-event inside a bubble dimension, it then doesn't have a measurable mass that can be defined in the overall weight of the ship.

The Time Lord Compendium and TARDIS schematics: http://time-lord-rassilon.deviantart.com/

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The key to remember that the configuration of the TARDIS changes - in Castrovalva they jettison about 30 percent of the ship to generate thrust. It is reasonable to assume that earlier in his adventures (the series) It may have been smaller.

But the previous mentions of the fact that the interior of the ship are not truly within the confines of the exterior are important to remember. I'd be willing to bet that the relative weight of the exterior shell can be altered, at least to a degree. It's been moved with relative ease too many times for it to be impossibly heavy by default.

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