How can space travel be like world travel?

[Bullgrit]

In your BullGrit example, BG grows, so of course he's a lousy unit of measure.

That's what she said.

Bullgrit

 

[Janx]

Not really. There are what are called "inflationary" models, in which there's a "period" before the appearance of normal matter, normal subatomic particles, and light, where the universe can grow to great size before there are any "things" in the universe relative to which we can measure speeds. The "speed of light" has no meaning in a universe in which light does not exist. *Time* doesn't even have a whole lot of meaning in an inflationary period, as what is inflating is spacetime - so time is inflating with space.

Inflationary models are widely, but not universally, accepted.

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So, instead of the Big Bang being caused by all universal matter being compacted and then exploding out, was it rather a case of Space Injection. All matter suddenly got space injected between it, causing the distance between any other object to increase?

 

[Umbran]

Why isn't there an absolute unit of measurement?

Because an absolute unit of measurement requires absolutely uniform space - the shape of space to be constant and the same in all places, and for all times. For most places on the surface of the Earth, in human history, it is "close enough" to assume that this is so. But it turns out not to be true, in general, on the scale of galaxies and the cosmos.

The King declares how long a foot, a mile is, etc. Sure its arbitrary, but once chosen it. works.

Ah, but you see, Einstein has made it clear to us that spacetime doesn't give a hoot what the King says. Time and space measurements are "relative" - meaning, they relate to your personal condition.

As Morrus mentions, they change with how fast you are moving. But that's not all - they also change with the gravitational gradient in the vicinity. So, how long a meter is depends on where you are, and how you are moving. Even if we start with identical copies of a King's Yardstick, if they are used in different places, under different conditions, they can give different answers.

For most things in human experience, the differences are negligible.

Right now, the Universe looks pretty flat. But, the effect can be measured locally - the orbit of Mercury is perturbed by this effect. Your GPS receivers take it into account as well.

 

[Morrus]

So, instead of the Big Bang being caused by all universal matter being compacted and then exploding out, was it rather a case of Space Injection. All matter suddenly got space injected between it, causing the distance between any other object to increase?

There wasn't any matter at that point - matter came later. There wasn't a bunch of matter "compacted".

 

[jonesy]

Getting back to the original topic:

How fast would space craft need to move for intergalactic travel to be like modern intercontinental travel

If we could figure out a cryogenic or stasis system, or something along those lines (robot bodies and computer brains?) the speed wouldn't be much of an issue. When you don't need to worry about acceleration too much the same amount of fuel gets you pretty much anywhere, eventually. Of course, if you then traveled back everyone you knew would be long dead, so you'd better bring your loved ones along for the ride.

Or, time travel. You don't need to worry about speed when you don't need to worry about time. If it was possible somehow.

Or, consciousness beaming. Figure out a way to download your mind into a computer, send your mind as a blueprint via laser beam to your destination, have it received there and written into a brain and body chosen for you. Instant travel, for you, since you'd only remember shutting down and waking up. Just hope there's no packet loss.

 

[Umbran]

So, instead of the Big Bang being caused by all universal matter being compacted and then exploding out, was it rather a case of Space Injection. All matter suddenly got space injected between it, causing the distance between any other object to increase?

Neither, really, at the Big Bang itself. The stuff we know of as matter, particles, sub-atomic particles - that all comes some time after the Big Bang. It may be fractions of a second after the BB, but the distinction is still kind of important, at least to physicists.

From there... upon consideration it is both like exploding out in some ways and your injection (though, I'd not call it that - it is less like having a syringe pumping space in-between things, and more like the space just increases). Space and matter go and in hand, so I'm not sure it is wise to discard either analogy fully.

 

[jmucchiello]

Or, consciousness beaming. Figure out a way to download your mind into a computer, send your mind as a blueprint via laser beam to your destination, have it received there and written into a brain and body chosen for you. Instant travel, for you, since you'd only remember shutting down and waking up. Just hope there's no packet loss.

Who exactly sets you up with a body and a brain on the other end before you beam out? And how are they contacted before you "laser" you conscience out there? Remember, in the earlier discussion, the stars you see aren't in the places your see them. They are elsewhere.

 

[jonesy]

Who exactly sets you up with a body and a brain on the other end before you beam out? And how are they contacted before you "laser" you conscience out there? Remember, in the earlier discussion, the stars you see aren't in the places your see them. They are elsewhere.

We can calculate where they really are. But yeah, needing someone on the other end first is a major flaw in the setup. It would be easy to implement (having the tech for it first) on a solar system scale, pretty hard on local stars scale, and increasingly harder from then on out, right up to impractical and impossible.

 

[Umbran]

If we could figure out a cryogenic or stasis system, or something along those lines (robot bodies and computer brains?) the speed wouldn't be much of an issue.

That might work for local interstellar transit, but not intergalactic.

Consider that the nearest galaxy is still 2.5 million light years away. Even traveling at 0.9c, it would seem to take something like a million years to get there from the traveler's point of view. Humans have not ever built anything to last a million years, much less something so complex as a starship.

Consciousness beaming, especially, fails on the intergalactic range - unless you have some FTL communication, your beaming is limited to light speed. It'd take a couple million years to reach the destination, and it only works if you can send the signal with such intensity that it can be detected when you get there.

 

[jonesy]

...and it only works if you can send the signal with such intensity that it can be detected when you get there.

I've been meaning to ask someone who knows more about that. How much does a light signal deteriorate travelling through space?

If you had a laser cannon and you fired it at Pluto, how much of the intensity would be lost? How about Alpha Centauri? Or Andromeda?