Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Travel through wormholes is possible, but slow

phys.org

Post reply on HN
Print view View original

81–90 of 190 posts

Re: Travel through wormholes is possible, but slow

#81

Post by nine_k »

piker wrote: post #51
eigenschwarz wrote: post #17

Earlier quoted context omitted.

The Average Null Energy Condition (ANEC) makes it so there can not be a traversable wormhole joining two otherwise disconnected regions of spacetime. So by construction, any infinite null geodesic (a light ray) which makes it through the wormhole must be chronal (causally connected). This means there can be no traveling faster than light over long distances by going through one.

So that's it, then? Some thing, say, a million light years away from another thing is in practice entirely inaccessible to civilizations existing on that other thing, requiring a minimum of a million years to reach?

This depends on what do you mean by 'inaccessible'.

Going there and back again, and telling your pals how things are 1000LY away is likely impossible.

Expanding your civilization to more and more habitable celestial bodies, slowly but relatively surely, is entirely possible. This is how e.g. plants colonize vast spaces, being limited by the speed of their growth often by inches per lifetime. (You should also consider the amount of resources the plats dedicate to it, and their success rate.)

Re: Travel through wormholes is possible, but slow

#82

Post by fooqux »

Retra wrote: post #72
Consultant32452 wrote: post #61

Earlier quoted context omitted.

I thought Hawking radiation was going the other direction, but that it doesn't carry information about the original mass/energy. Is that right?

I don't think there's a definitive answer there, nor any reason to believe Hawking radiation is produced inside an event horizon, rather than just outside it. The event horizon is pretty much defined by the boundary that radiation will not escape across, so I wouldn't assume Hawking radiation behaves any differently with respect to it.

I believe you're right that the jury is still out about information loss.

However, I believe that the energy from Hawking Radiation comes from the black hole itself. In that case it doesn't matter if it's inside or outside the event horizon- it's still 'leaking' energy/mass.

Re: Travel through wormholes is possible, but slow

#83

Post by FakeComments »

lupire wrote: post #68
FakeComments wrote: post #48

Earlier quoted context omitted.

That’s not what I was asking. I was asking about the particular usage of the average null energy condition as justification to rule out wormholes: why isn’t that just begging the question by assuming your conclusion? and how does that particular assumption actually lead to the conclusion there can’t be wormholes? It’s interesting the downvotes for asking someone to support a scientific claim, and be clear where they’…

That's right. When you have a mathematical theory, there are often extremal cases that predict strange things that have never been observed. At this point you have a choice to make: 1) Assume the mathematical theory is too permissive, and rule out the things you have no reason to exist, and hope to find a more elegant theory (on the controversial metaphysical assumption that simpler/elegant theories are more likely t…

Okay — and just to be clear, there’s nothing problematic to me about simplifying assumptions or effective theories.

Both are important tools for making predictions tractable.

But when we lose sight of what are conclusions, what are strongly justified assumptions, and what are simplifying assumptions we don’t have justification for (or even know to be untrue), we begin to create fundamentally inaccurate models or wrongly shut down others’ avenues of inquiry.

This happens in economics and business quite often, but simplifying assumptions become orthodox truth with surprising frequency in hard sciences like physics, as well.

Re: Travel through wormholes is possible, but slow

#84

Post by xvector »

nkrisc wrote: post #76
piker wrote: post #51

Earlier quoted context omitted.

So that's it, then? Some thing, say, a million light years away from another thing is in practice entirely inaccessible to civilizations existing on that other thing, requiring a minimum of a million years to reach?

Well, theoretically they could load their civilization up on a giant ship and move their civilization there over the course of a million years. Likelihood of success? Probably not great, but possible.

Everyone is missing the obvious solution. If we're talking about tech this fantastical, the best idea is to ditch our ephemeral biological bodies, jump onto a synthetic medium, and call it a day.

Hit pause so the journey takes a fraction of a second, or spend 1000Y in a VR - do whatever you want. I don't see a future where we're this advanced yet still content with our frighteningly fragile bodies.

Re: Travel through wormholes is possible, but slow

#85

Post by nine_k »

lupire wrote: post #65
eigenschwarz wrote: post #62

Earlier quoted context omitted.

I definitely get your point. One difference between theoretical physics and just math is we have since we use math as just a tool to describe the world, we still have to input physical assumptions to make any sense of what we see. There are many instances of things being mathematically "OK" but we don't think physically exist. See "White Hole" for instance. I will try to give a better explanation later today! Funny e…

Who is the "we" who thinks White Holes don't exist? https://en.wikipedia.org/wiki/GRB_060614

Black holes are hard to notice, except by side effects, but we know great many of them, end even portrayed one.

White holes would be relatively hard to miss, because they must be shining very brightly. One of the current theories suggests that the big bang (or "a big bang") was a white hole: every black hole is a white hole producing a big bang a parallel universe. We've already had ours, and are lucky enough to still register its echo as the CMB.

Re: Travel through wormholes is possible, but slow

#87

Post by zspade »

swebs wrote: post #66
piker wrote: post #51

Earlier quoted context omitted.

So that's it, then? Some thing, say, a million light years away from another thing is in practice entirely inaccessible to civilizations existing on that other thing, requiring a minimum of a million years to reach?

On the bright side, due to time dilation, you can still make the trip in your lifetime.

If by the bright side you mean you would only make it there it there as pure energy. Mass is converted to energy as it approaches C (Light Speed). Though getting mass to actual light speed would require infinite energy, so that point is moot.

Let's say you get to 96% C. You would experience 28% of the journey. Taking into account the the time to speed up and slow down from C, you're looking at over 290k years from the perspective of the passengers.

At 99% C, you would experience over 14% of the journey (About 142k years).

Re: Travel through wormholes is possible, but slow

#88

Post by stcredzero »

swebs wrote: post #66
piker wrote: post #51

Earlier quoted context omitted.

So that's it, then? Some thing, say, a million light years away from another thing is in practice entirely inaccessible to civilizations existing on that other thing, requiring a minimum of a million years to reach?

On the bright side, due to time dilation, you can still make the trip in your lifetime.

You don't get much time dilation until you start hitting speeds mostly exclusive to accelerated subatomic or nuclear particles. It's nearly zero until you get past 0.5 c.

https://www.fourmilab.ch/cship/timedial.html

Re: Travel through wormholes is possible, but slow

#89

Post by pontifier »

philipov wrote: post #56
magduf wrote: post #54

Earlier quoted context omitted.

It kinda sounds like we're actually in a gigantic black hole...

It really does feel like the two concepts are related, but there are enough differences that you can't just say we're inside a black hole. For one thing, the inside of a cosmological horizon corresponds to the outside of a black hole. I do think the similarity is part of what drives so many physicists to study black holes and quantum gravity, though. Horizons are a consequence of dynamical spacetime, but a deeper the…

This is actually very similar to what I've heard an observer falling into a black hole would experience... as you fall in, space curves to bend all outward worldlines back to the singularity. You never experience the horizon itself even while passing it, but would see the horizon wrapping itself around you in all directions.

Re: Travel through wormholes is possible, but slow

#90

Post by saagarjha »

zspade wrote: post #87
swebs wrote: post #66

Earlier quoted context omitted.

On the bright side, due to time dilation, you can still make the trip in your lifetime.

If by the bright side you mean you would only make it there it there as pure energy. Mass is converted to energy as it approaches C (Light Speed). Though getting mass to actual light speed would require infinite energy, so that point is moot. Let's say you get to 96% C. You would experience 28% of the journey. Taking into account the the time to speed up and slow down from C, you're looking at over 290k years from th…

> Mass is converted to energy as it approaches C (Light Speed).

Uh, I think it's the other way around: the energy you pump in becomes additional mass.

Post reply on HN