avz

Phones can easily be oriented either way, unlike most laptop and workstation screens.

Majority of views certainly come from people whose eyes are horizontally next to each other and therefore whose field of view has a greater extent in the horizontal rather than vertical direction.

Admittedly I don't understand where the vertical recording fad comes from. Personally I take pictures and photos that are almost exclusively horizontal except in rare cases like taking a picture of a very tall building.

Well, the may have understood the concept of "running out of stuff" and yet not realize it naturally belongs with numbers (of which they would have known other examples like one and two). I can imagine ancient folks putting the notion of "running out of stuff" with ideas such as "hungry", "empty", "dead" etc. Formation of the more abstract concept of zero-the-number is certainly a few cognitive experiences further down a line.

The perspective of modern computer science (with its zero-based indexing etc) or modern algebra (with its need for neutral element for addition) certainly makes it clear that zero is just another integer. However, without those perspectives I doubt it is so obvious.

For example, people normally count things by starting from one, so, at least following this usual procedure, counting to zero is technically speaking impossible. Also, we can't distinguish between zero apples and zero oranges, but we can tell two apples and two oranges apart.

In fact, even with the perspective of modern algebra zero remains special. For example, it is the only element of a field without a multiplicative inverse.

I'd be surprised if zero didn't take any extra effort to discover. It's clearly different than other integers.

The OP said "There's more time between the last Stegosaurus and the first T-Rex" which computes to 145-72 = 73 and "then (sic) there is between the last T-Rex and us right now." which computes to 66-0=66. Note that 7 million years is about 10% of the timescales involved, so perhaps not something to be dismissed as "scientific error".

Technical detail: Having crossed all meridians is generally not considered the proper criterion for circumnavigation since this is trivially done near the poles. The definition I have come across include a loop that partitions Earth's surface into two parts of comparable area.

Looks good to me as a rough back-of-the-envelope calculation to get the orders of magnitude right (the speed will go down as the object is climbing out of Sun's gravity well).

However, you're still missing a guesstimate for alien lifespan. Do you have reasons to believe they live shorter than 33552 Earth years?

Also, is 38 km/s really the top speed for hypothetical interstellar ship?

I imagine aliens that live on average 870 Earth years (~10x average lifespan of a female Japanese) and travel at 9,000 km/s. They can easily make Sun-Proxima Centauri trip six times in a lifetime.

It seems to me that "the universe" is not an appropriate term for our close planetary neighborhood.

There is a difference between an interstellar object passing within 85 times the distance to the Moon (so closer than Mars at closest approach to Earth) and say a supernova thousands or millions of light years away (and hence thousands or millions of years ago).

I don't know where the universe begins, but I'd say Low Earth Orbit and the Moon don't qualify while Proxima Centauri does. For reference:

Distance from ground to space: ~100 km

Distance from California to Australia: ~12,000 km

Distance to the Moon: ~400,000 km

Distance to 'Oumuamua's closest approach: ~33,000,000 km

Distance to Mars at closest approach: ~55,000,000 km

Distance to the Sun: ~150,000,000 km

Distance to Neptune: ~4,500,000,000 km

Current distance to 'Oumuamua ~5,000,000,000 km

Distance to Sedna: ~13,000,000,000 km

Distance to Proxima Centauri: ~40,000,000,000,000 km

> Whoever has more weapons get the land.

Aliens might not actually be land-based creatures like us. Those who evolved on planets entirely covered by liquid (water or otherwise) might even find the idea of "land" fairly strange.

(It's actually quite interesting to ponder the stages of discovery that liquid-based intelligent aliens might go through. First they might discover air (and land if available) and only after that space as another outer layer. I suppose that adds extra thrill we didn't have. Supposing of course that conditions there allow gas and liquid to exist as separate phases. Planets above criticality would probably be weirder still? Would any bottom rocks under the supercritical fluid still count as land - as opposed to "sea floor"?)

What does "habitable" mean in the context that includes multiple alien species that evolved independently on different planets? After all, alien fishalikes that might have evolved in the methane lakes on Titan are unlikely to share our idea of "habitable"...

I think the situation with interstellar travel is well summed up in this conversation between TARS and Cooper as they attempt to dock at Endurance (intentional pun hiding in movie title):

TARS: It's not possible.

Cooper: No, it's necessary.

It seems impossible, but if we don't pull it off we die. And I don't mean we the few folks on HN. I mean everyone.

Earth is a graveyard of species. Nearly all (99% IIRC) species that ever existed have gone extinct (most before we showed up). As a species, we can't stay here and live. A 9-mile thin layer of gas over a single small planet is just not a reliable long-term basis of survival. In fact, the fragility of our tiny little habitant is on display right in front of us this century.

I agree with your conclusion, but I always find that these discussions miss the role of medical science.

The key parameters governing feasibility of human interstellar travel are the average human lifespan in years and typical interstellar distance in lightyears. These are roughly 72 years and 5 lightyears, respectively. So it takes about 70% of a human lifespan to travel a typical interstellar distance at 10% of the speed of light. This is... not great.

The key realization is that the relationship of these two numbers is in a sense an accident of biology and astronomy.

It is usually assumed that future technological progress might enable travel at a large fraction of the speed of light, but it is often missed that future medical progress might extend human lifespan to say 400 or 1000 years.

A scarier realization is that intelligent aliens might have natural lifespan that make interstellar travel seem far more practical.