Space is expanding, pushing all the stuff in the universe apart. But "pushing" is not really the right word, because the objects aren't actually being accelerated.

Instead, new space is being created between all objects. This can cause the distance between two objects to increase "faster" than the speed of light, without either of the objects actually moving.

The first few paragraphs of https://en.m.wikipedia.org/wiki/Expansion_of_the_universe do a reasonably good job at describing what I assume is the source of your puzzlement (namely how can something recede faster than the speed of light)

Due to the big bang the universe is expanding... but you’d expect the expansion to be slowing down due to the drag of gravity. However, since the 1990s we’ve observed that the universe’s expansion is accelerating - the theory is that a force called “dark energy” is causing this acceleration. If the acceleration continues, there will be a point where distant galaxies will be accelerating away from each other at the speed of light. Since light is the universe’s “speed limit”, we would not be able to travel to these galaxies with known physics because even traveling at light-speed the galaxy we’re going to would be stretching away faster. Locally, however, due to gravity, it sounds like the paper is saying we would have regions of dense galaxies that stay closer together. Islands of matter in a sea of dark energy.

The idea that humanity will ever travel even to the nearest star is pure fiction.

Anyone who thinks otherwise just fails to grasp the distances involved. They are so large as to be beyond understanding.

The idea that humanity won't ever travel even to the nearest star is pure fiction.

Anyone who thinks otherwise just fails to grasp exponential growth. They are so large as to be beyond understanding.

"...won't ever... is pure fiction"

Do you mean to say humanity certainly could travel to the nearest star?

I'm skeptical that anything resembling humanity could because everlasting exponential growth requires infinite resources. And humanity evolved on an abundant--but far from infinite--gravity well.

I was mostly making a point that grandiose statements can be rebutted by similar (in this case, changing 3 words) grandiose statements.

To answer your question though, the main problem with space travel isn't physics (assuming you are ok with long travel times), it's economics. We have sent astronauts to the moon and probes all across the solar system. The main reason we don't do more though is because of how expensive it is. However, a thousand years of 2% growth (not a given but again, grandiose) means we would have 400 million times more money to possibly spend on space travel. A NASA budget 400 million times larger could certainly build and send a spaceship 4 light years to alpha centauri.

Now how long will we sustain exponential growth? Well that's anyones guess but I don't see us becoming resource constrained for a long long time. The sun produces 10^13 more energy than the world used in 2013 according to [0] and we have plenty of resources in the solar system to build with (and we can recycle more).

[0]: https://www.quora.com/How-much-energy-does-the-sun-produce-p...

> To answer your question though, the main problem with space travel isn't physics (assuming you are ok with long travel times), it's economics.

I'd argue it's biology, not physics. Sending a rock to another star is easy. Sending a rock that can send back data is probably possible with our technology, but it's unlikely it would retain data transmission capabilities long enough to actually report back from another star. Sending a bunch of humans and keeping them alive the entire journey? It's not clear we can do that for a round trip to Mars, let alone an interstellar journey.

The 2 biggest health problems that I am aware of with spaceflight are due to weightlessness and radiation. However, both can be probably be solved with enough money (make the spaceship a rotating one with artificial gravity and add more shielding). There might be others but I am pretty confident you could engineer your way past each and every one given a large enough budget.

You're sort of missing the biggest health problem of all: how do you make a self-sustaining closed ecosystem?

True, I was thinking more in the context of the mars trip you mentioned where you can generally take the resources you need for the trip. For intersteller travel, you would need to make it self sustaining since the travel times are so long and that would be extremely expensive.

The article suggests moving stars.

Let's be a bit more positive on Humanity's progress eh?

Humanity is on the cusp of three major technological breakthroughs that will quite literally change everything.

1) AI. Even if we don't reach ASI in the near term, we'll have ANI to help us research new technologies in months/years rather than decades.

2) Asteroid Mining. Whether it's Musk/Bezos/A. N. Other, the very first time someone brings down an asteroid. It will herald the dawn of abundance for precious metals. What will happen to prices is another topic. But this will allow researchers to develop even more exotic materials.

With better materials resistant to heat, more conductive elements, etc, etc. Humanity be able to build what can only be dreamt of.

3) 7 Billion (now). 13 Billion with Mars, 50+ Billion with Europa, Titan, Ganymede, etc, etc, etc. There will be a time where Humans will stretch beyond this solar system. Imagine how many breakthroughs will be possible with 100m researchers and AI trying to crack something?

What will make this possible? With 1 and 2, we'll be able to finally crack fusion reactors. This will enable faster space travel than with current engines. Habitats will evolve from those initial Mars missions and will sprawl into mega cities. Who knows, there may even be Luxury apartments hovering in the upper atmosphere of Venus.

All this progress is exponential and if you stop to look around. The seeds are being sewn right now. By 2050, some things we consider Sci-fi will be reality.

Oh and I'll just throw this one in.

4) Nasa has been doing some work on the Alcubierre drive. Who is to say, that the issues that cannot be surmounted now, will be in the future? For those that want to know more. I'll leave a channel that goes into such things [0].

[0]: https://www.youtube.com/channel/UC2kkCGRqZWaSIK3BmLC8vaw/vid...

> 2) Asteroid Mining. Whether it's Musk/Bezos/A. N. Other, the very first time someone brings down an asteroid. It will herald the dawn of abundance for precious metals. What will happen to prices is another topic. But this will allow researchers to develop even more exotic materials.

Say what? The idea that asteroid mining will enable material science revolutions is fanciful. We're not exactly short on metals (even precious metals). And interplanetary space is less extreme than environments we can create in terrestrial situations, so we're not going to find weird new stuff by poking around asteroids.

>We're not exactly short on metals (even precious metals).

Last I checked, the price of most metals was greater than zero. They're commodity markets, so that means they're scarce. If you mean "available at any price," then we were not short on iron during the Bronze age or short on Aluminum during the early 1800s.

Well, it is possible that if rare and expensive metals become dirt cheap, new exotic alloys may be developed that were previously economically inconceivable.

I don't know how likely this is. I imagine plenty of research has already been done on exotic alloys, however I wonder how much that research has been affected by economic constraints.

Alcubierre drives require exotic matter which is not quite ruled out by the laws of physics. Hopefully they don't require Jupiter-sized masses of the stuff, although some have suggested as much. However, that solved, there are two slight problems with this idea. One is that FTL inherently violates causality, which is sort of a problem. The other is that the spacecraft is expected to pick up and accelerate with it basically any matter it runs into along its superluminal path, releasing these as a spectacular shower of near-c particles whenever it stops. Your other speculations have their own defects, but I'll let others address them.

The distance to the moon is already beyond intuition, but you can still understand how to get there by doing calculations. If the numbers say that it's possible then it's possible.

My vote is still with the brain in a jar (or something close to it). Fewer resources, less area, and much of the life support equipment could be shared between many individuals. There's reason to believe it would extend lifespans as well, provided that an entirely virtual life could be made worth living.

I honestly think we'll achieve this long before we're able to properly or effectively simulate a brain with computers of any kind.

the _nearest_ star is actually quiet close :-]

thats pretty accurate as far as current technology goes, but then again with a few additional centuries of research we never know what we end up achieving.

We could just about do interstellar now if an existential threat called for it. Project Orion or a nuclear salt water rocket are both possible already.

There is a theory that the universe is expanding faster and faster. At some point in the future, stars would be moving away faster than the speed of light and we couldn't ever see them again or reach them.

How could they be moving faster than the speed of light?

Imagine two RC cars driving in opposite directions on a crumpled up, (virtually) infinitely large blanket with an uncountable number of ripples. The cars' top speeds are 10 MPH. On top of each car is an ant watching the other car.

Both cars start driving off at 10 MPH in opposite directions. From an ant's perspective on top of one car, the other car looks to be going 20 MPH away from it. Then someone starts pulling the blanket underneath the cars from opposite ends at 5 MPH. Now it looks like the other car is going 30 MPH. Now imagine for each ripple on that blanket, another hand appears and starts to pull, and the outer edges are pulled at 5MPH from the reference point of the nearest ripple.

From the perspective of an ant on one end, it can eventually get to the point that the other car is warping off at 100MPH or more. And as this blanket spreads out more and more, things speed up more and more as well. The cars never technically exceed their speed limits of 10 MPH, but the space that they occupy is being pulled apart in a way that they seem to be exceeding 10 MPH from each other's perspectives.

Anything which moves through space-time is restricted to moving at the speed of light. Space-time itself can warp causing objects to "move" away from each other faster than the speed of light.

Think of ants crawling on the surface and a balloon which is being blown up.

Because while matter cannot move faster than the speed of light the universe itself is allowed to expand faster than the speed of light. Think of the spacetime fabric stretching so fast light cannot cover the increased distance. The universe is essentially creating more distance between objects.

Another way to think of it is velocity of an object is derivative of position in space over time. If space itself is moving your position relative to it isn't changing.

I still can't intuitively understand this. If two objects ar stationary relative to each other, the expansion implies that at some point, the distance between those two objects will increase (without either of those objects having moved).

So space is being somehow created?! What if i have a large object, will the length of that object increase? Or will it break up?

The object is bound together by electromagnetic forces, and the local group is bound together by gravity. These forces are much stronger than the expansion of the universe (cosmological constant), but the expansion of the universe manifests as a tiny tiny outward pressure term (too small for us to detect). It makes every atom/orbit a little bigger by changing the equilibrium point, but they don't to grow in size because the force isn't increasing.

If the cosmological constant were much larger than it is, atoms would have never formed at all.

I think you are using a concept of space-time that is quite limited. You are at most using concepts from Einstein's Special Relativity. Everything changed with General Relativity.

Space is not "created", space-time is warped. Gravity is the deformation of space-time by mass/energy. The distance from point A to point B is measured by the time it takes for a light ray to get from A to B using the shortest path. But if you move objects with mass (or with energy) near A and B, the shortest path will change. Also, it's easy to measure distance in seconds when you know the speed of light.

If I understand this correctly, you're talking about something similar to Star Trek's Warp Drive (or the Alcubierre drive, for something less fictional). Instead of stars and galaxies moving at the speed of light, the space around them expands and the expansion accelerates at a rate that will eventually make the speed of expansion larger than the speed of light. Or in other words, stars and galaxies will continue to move at their sub-luminar speed, but the space in which they exist will expand so fast that the expansion will cause the distance between them to increase at such a rate that light will not be able to keep up.

[Edit: and, er, all that has something to do with dark energy?]

OK, but in that case, and if we still exist as a technological civilisation at that time (very doubtful) we might be able to use the effect for our own benefit. By building warp drives and er, not-quite-travelling faster than light, by expanding space around a ship, etc.

Warp drive solves a plot problem, it doesn't do anything to mitigate violating causality.

And if they can, why can’t we and catch them? I mean we are in spacetime. If it stretches we stretch too!

Right now the only serious effort to consider how to do so is the Alcubierre metric and its variations. Nobody knows how to build one, or what matrials could build one, or how to turn it on or off. Unless you have a cunning way to cheat, such as making the inside bigger than the outside, it requires in excess of minus the rest mass of the observable universe for a plausible sized object. There are further objections, but above my level.

So would the light from those stars also be moving outward faster than the speed of light?

No. In fact, if two objects are far enough apart, then the amount of new space created between them will be so great that light will never be able to travel between them. Neither object will ever be able to see the other.

It's really hard for me to imagine how a flashlight on a distance plant could be moving away from me faster than the speed of light but the emitted light is going slower.

No. It's color shifted though.

https://en.wikipedia.org/wiki/Relativistic_Doppler_effect

Just like the sound of an ambulance.

the universe is expanding and the expansion is accelerating