# Alien Size
**URL:** https://boards.straightdope.com/t/alien-size/129409
**Category:** Factual Questions
**Created:** [September 24, 2002, 4:03am UTC](https://boards.straightdope.com/t/alien-size/129409 "2002-09-24T04:03:14Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@PetW](https://boards.straightdope.com/u/PetW)
#### Post date: [September 24, 2002, 4:03am UTC](https://boards.straightdope.com/t/alien-size/129409/1 "2002-09-24T04:03:14Z")
I wasn’t sure whether to put this in GQ or GD, so if it’s in the wrong forum I apologize. Anyways:
If one day we DID meet aliens from another planet, what are the chances that their size would be anywhere near ours? I mean, on another planet, isn’t it just as likely that they could be 1 inch tall or a few miles wide? What environmental conditions would encourage larger sizes?
---
### Author:  [@Musicat](https://boards.straightdope.com/u/Musicat)
#### Post date: [September 24, 2002, 4:16am UTC](https://boards.straightdope.com/t/alien-size/129409/2 "2002-09-24T04:16:02Z")
> [@](#):
>
> \*Originally posted by PetW \*
> What environmental conditions would encourage larger sizes?
How about less gravity, for starters?
---
### Author:  [@Musicat](https://boards.straightdope.com/u/Musicat)
#### Post date: [September 24, 2002, 4:24am UTC](https://boards.straightdope.com/t/alien-size/129409/3 "2002-09-24T04:24:10Z")
> [@](#):
>
> \*Originally posted by PetW \*
> What environmental conditions would encourage larger sizes?
How about less gravity, for starters?
---
### Author:  [@Musicat](https://boards.straightdope.com/u/Musicat)
#### Post date: [September 24, 2002, 4:31am UTC](https://boards.straightdope.com/t/alien-size/129409/4 "2002-09-24T04:31:31Z")
> [@](#):
>
> \*Originally posted by PetW \*
> What environmental conditions would encourage larger sizes?
How about less gravity, for starters?
---
### Author:  [@Musicat](https://boards.straightdope.com/u/Musicat)
#### Post date: [September 24, 2002, 4:39am UTC](https://boards.straightdope.com/t/alien-size/129409/5 "2002-09-24T04:39:04Z")
I swear to the god of the aliens, I clicked “submit” only once. It took forever, but I resisted the temptation to hit it again. Yet I got 3 posts???
---
### Author:  [@Ranchoth](https://boards.straightdope.com/u/Ranchoth)
#### Post date: [September 24, 2002, 4:54am UTC](https://boards.straightdope.com/t/alien-size/129409/6 "2002-09-24T04:54:38Z")
Well, aside from a limit on how small intelligent extraterrestrials could be (For instance, you probably couldn’t squeeze enough neurons in a brain the size of a sugar granule to support a human-level intelligence), I imagine it would be hard to give “odds” on how many intelligent species would be human sized, seeing as you’d be working with a statistical sample of 1.
Although…if you want to fudge it, you might include the top 20 or so most intelligent animals on Earth after humans. Everything from, say, Chimpanzees to Dogs, and try and work out an average size from them. (The Whales would probably skew the results, though) They’d be the closest things to “intelligent aliens” we have to compare ourselves with.
Best of luck,
Ranchoth
---
### Author:  [@Smeghead](https://boards.straightdope.com/u/Smeghead)
#### Post date: [September 24, 2002, 5:42am UTC](https://boards.straightdope.com/t/alien-size/129409/7 "2002-09-24T05:42:34Z")
Insufficient data. Please explore galaxy and try again. Thank you.
---
### Author:  [@Duckster](https://boards.straightdope.com/u/Duckster)
#### Post date: [September 24, 2002, 6:56am UTC](https://boards.straightdope.com/t/alien-size/129409/8 "2002-09-24T06:56:42Z")
You did say _another planet_ didn’t you?
Damn!
I was thinking placing one of those multi-colored “how tall was the robber” measuring tapes on the door jamb of the customs and immigration exit and just kinda observe as they entered the general concourse.
Silly me. :smack:
---
### Author:  [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)
#### Post date: [September 24, 2002, 12:40pm UTC](https://boards.straightdope.com/t/alien-size/129409/9 "2002-09-24T12:40:48Z")
If they were from a similar gravity/chemistry planet, my guess is that they’d be about the same size – you need similar levels of complexity, etc., so you’d think that brains would end up being about the same size. Creatures that are too small haven’t got enough brain material to be intelligent, and have to spend too much time foraging. I think Asimov did at least one column on this at some point.
On the other hand, if circumstances are different, I can easily see how a different size could evolve. See Hal Clement’s Mesklinites in **Mission of Gravity** and **Star Light** , or the effects of high gravity and entirely different chemistry (nuclear interactions!) in Robert Forward’s **Dragon’s Egg** and **Star Quake**
---
### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [September 24, 2002, 12:40pm UTC](https://boards.straightdope.com/t/alien-size/129409/10 "2002-09-24T12:40:59Z")
I started a thread on this subject ages and ages back; there are certain limiting factors because not everything ‘scales’ in exactly the same way - if you have a planet with much much less gravity than Earth, then it can’t hold an atmoshpere, surface tension of liquids and viscosity of air are much bigger factors at a smaller scale, perhaps most importantly fire doesn’t scale down at all well; aliens the size of mice would not find it nearly so easy to manage fires large/hot enough to smelt metal ores.
---
### Author:  [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)
#### Post date: [September 24, 2002, 1:34pm UTC](https://boards.straightdope.com/t/alien-size/129409/11 "2002-09-24T13:34:08Z")
If they were from a similar gravity/chemistry planet, my guess is that they’d be about the same size – you need similar levels of complexity, etc., so you’d think that brains would end up being about the same size. Creatures that are too small haven’t got enough brain material to be intelligent, and have to spend too much time foraging. I think Asimov did at least one column on this at some point.
On the other hand, if circumstances are different, I can easily see how a different size could evolve. See Hal Clement’s Mesklinites in **Mission of Gravity** and **Star Light** , or the effects of high gravity and entirely different chemistry (nuclear interactions!) in Robert Forward’s **Dragon’s Egg** and **Star Quake**
---
### Author:  [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)
#### Post date: [September 24, 2002, 1:41pm UTC](https://boards.straightdope.com/t/alien-size/129409/12 "2002-09-24T13:41:53Z")
If they were from a similar gravity/chemistry planet, my guess is that they’d be about the same size – you need similar levels of complexity, etc., so you’d think that brains would end up being about the same size. Creatures that are too small haven’t got enough brain material to be intelligent, and have to spend too much time foraging. I think Asimov did at least one column on this at some point.
On the other hand, if circumstances are different, I can easily see how a different size could evolve. See Hal Clement’s Mesklinites in **Mission of Gravity** and **Star Light** , or the effects of high gravity and entirely different chemistry (nuclear interactions!) in Robert Forward’s **Dragon’s Egg** and **Star Quake**
---
### Author:  [@Go\_alien](https://boards.straightdope.com/u/Go_alien)
#### Post date: [September 24, 2002, 1:57pm UTC](https://boards.straightdope.com/t/alien-size/129409/13 "2002-09-24T13:57:40Z")
I know but I’m not telling. It would blow my cover. 😃
---
### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [September 24, 2002, 2:09pm UTC](https://boards.straightdope.com/t/alien-size/129409/14 "2002-09-24T14:09:07Z")
It’s false to assume that their brains would be of similar construction to ours; surely it can’t be impossible for a much more compact configuration to exist which still offered a similar level of complexity.
---
### Author:  [@Squink](https://boards.straightdope.com/u/Squink)
#### Post date: [September 24, 2002, 2:39pm UTC](https://boards.straightdope.com/t/alien-size/129409/15 "2002-09-24T14:39:46Z")
How would an alien creature a mile wide get rid of waste heat ? The [surface to volume ratio](http://www.tiem.utk.edu/~gross/bioed/bealsmodules/area_volume.html) places constraints on size, no matter what planet you are from.
---
### Author:  [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)
#### Post date: [September 24, 2002, 2:41pm UTC](https://boards.straightdope.com/t/alien-size/129409/16 "2002-09-24T14:41:53Z")
> [@](#):
>
> It’s false to assume that their brains would be of similar construction to ours; surely it can’t be impossible for a much more compact configuration to exist which still offered a similar level of complexity.
I don’t assume the construction is the same. It’s a “hand-waving” argument that _probably_ organic brains, whatever their construction, would require about the same size to store info. That’s not assuming the same sort of construction, but just based on how many information-storing chemical items you can fit in a given space.
---
### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [September 24, 2002, 3:00pm UTC](https://boards.straightdope.com/t/alien-size/129409/17 "2002-09-24T15:00:27Z")
I can see where you’re coming from (and I’m not really qualified in any relevant fields so maybe I should just shut up), but are the information storage methods used by the mammalian brain particularly efficient space-wise, from the POV of a biochemist?
---
### Author:  [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)
#### Post date: [September 24, 2002, 3:19pm UTC](https://boards.straightdope.com/t/alien-size/129409/18 "2002-09-24T15:19:00Z")
> [@](#):
>
> I can see where you’re coming from (and I’m not really qualified in any relevant fields so maybe I should just shut up), but are the information storage methods used by the mammalian brain particularly efficient space-wise, from the POV of a biochemist?
I dunno. I’m not really qualified, either – I’m not a biologist or biochemist, just a dumb physicist. That’s why my arguments are “hand-waving”. It would make an interesting basis for a science fiction novel if you could find a more efficient way to pack more computing potential in a smaller space – or maybe a good paper for “Nature” or “SCience”.
It would make for an interesting upfdated version of A. Merritt’s **The Metal Monster** , in which metal-based life exists on earth. Only in this case, self-assembling microcircuits enable the metal creatures to be as intelligent as people, but insect-like in size.
---
### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [September 24, 2002, 3:19pm UTC](https://boards.straightdope.com/t/alien-size/129409/19 "2002-09-24T15:19:22Z")
> [@](#):
>
> \*Originally posted by Squink \*
> \*\*How would an alien creature a mile wide get rid of waste heat ? \*\*
Very large ears?
---
### Author:  [@toadspittle](https://boards.straightdope.com/u/toadspittle)
#### Post date: [September 24, 2002, 5:32pm UTC](https://boards.straightdope.com/t/alien-size/129409/20 "2002-09-24T17:32:44Z")
Water-dwelling creatures could be much larger, obviously, and water would prove a much better cooling mechanism than air, to answer Squink’s question. Already, mammals here need to insulate heavily and have specialized circulatory systems to manage ocean waters.
But we, naturally, thing of ourselves. Who says the creature has to be warm-blooded? Perhaps they spend a lot of the day getting in and out of sunlight to stay to the right operating temperature, like iguanas or snakes. Or that the planet’s climate is even slightly similar? What if the planet’s equator is only as warm as June in Nome, and is the only habitable region? What if the animals need to conserve as much heat as possible? A larger animal might do better.
Being in water poses problems insofar as following our route through technology–fire, metalwork, spaceflight, etc.–but perhaps they would be intelligent but with a low technology level. I’d assume that, if they had to live in the water all the time, we’d be the ones visiting their planet first, not vice-versa.
[Next page](https://boards.straightdope.com/t/alien-size/129409.md?page=2)