# Tag Info

9

Irrepspective of the amount of negative mass matter required, it's still a fact that these schemes require negative mass matter to work, and negative mass matter is not known to exist. And there are still problems with faster than light travel that you would have to resolve--in particular, that a solution like this would enable you to construct a time ...

8

Spacetime can dynamically evolve in a way which apparently violates special relativity. A good example is how galaxies move out with a velocity v = Hd, the Hubble rule, where v = c = Hr_h at the de Sitter horizon (approximately) and the red shift is z = 1. For z > 1 galaxies are frame dragged outwards at a speed greater than light. Similarly an observer ...

7

I don't understand why we are able to see and measure curvature / warping of space at all. The Earth's surface is curved and this can be observed via the vast number of pictures of the Earth from space that now exist. However, the surface curvature can also be "seen" via measurements on the surface itself. For example, if one were start at the North ...

5

Curvature affects how objects in the universe move and interact with one another, and these effects can be measured. Take, for example, the phenomenon of gravitational lensing. Because spacetime curvature can deflect the path of light, we can potentially observe light coming from objects that are directly behind other objects. Here's a nice picture. As ...

5

The interior of the bubble is causally disconnected. It's not possible for the bubble to be turned off or steered from the inside. But there is no reason it cannot be affected from an outside agency at a pre-planned points, or even simply have a finite lifetime, naturally deteriorating to stop at the intended destination. that upon traveling to some ...

3

This is more of a meta answer, since it isn't really Physics, but it got a bit long to put in a comment. You say: I have heard many physicists (ex:- Michio Kaku) saying "Warp speed" from Star Trek doesn't violate any known physical laws. You need to think about precisely what this statement means. If we take the Alcubierre drive as an example it is a ...

3

It's very, very highly likely that none of these schemes are workable for the following reasons: Superluminal travel violates causality. You can talk about "general relativity loopholes" all you want, but you can always envision that the "warp region" is going to be confined to a finite-sized subspace of the whole spacetime, and outside of this region, ...

3

Relativistic effects happen when you travel near light speed through space-time. With the Alcubierre drive, you don't travel through space-time, but remain stationary and the space-time around you is warped in a way that brings you closer to your destination. So if it only took a week for you, it would only take a week for your observers. It'd be like if ...

3

By "heat" I'm going to assume you mean electromagnetic radiation, because outside of the interiors of stars and other similarly dense regions, heat cannot be conducted or convected. The answer is simply : No. Dark matter cannot be tiny bits of matter that we cannot see. To help you understand it better, let me explain a bit of history first - Dark matter ...

3

Heat can't just live in the vacuum. Because heat is a form of energy and energy is equivalent to mass, heat has to have a material carrier. The most "neutral" type of heat that you probably meant is the electromagnetic radiation. Dark matter can't be made out of electromagnetic radiation because it would escape, in 100,000 years, away from the galaxy. ...

2

General Relativity deals with curvature of Spacetime, not just curvature of Space. You can't ignore time because clocks are affected throughout the universe. Spacetime events are what we measure and are independent of observers. Now, let's come to point: You're asking why we're able to measure effects of Spacetime curvature with classical way when reference ...

2

If you start out in a flat Minkowski spacetime and begin to distort it to create an Alcubierre bubble, you won't actually be able to travel to anywhere that wasn't in the future light cone of your position immediately before you started work. For example if you have a network of clocks synchronized in the rest frame of the galaxy, and in 2000 you start work ...

2

What is the deal with the nonstop Alcubierre warp drive questions here? Superluminal speeds relative to what? If you're talking about gravitational waves, you have a weak wave, and a background metric to measure speeds. If you have a solution that differs nonlinearly from the minkowski spacetime, the disturbances are both the thing moving and the ...

2

Pete, please elaborate your question, the original paper describes by Miguel describes how one can travel back and to a destination using the warp drive. The space in front is contracted to get closer to the destination, and the space behind is expanded. For getting out of the bubble, let's use the picture below: The bubble is created, so to speak, ...

2

Exotic matter is matter with negative energy density, or to be more precise, where the energy density tensor trace invariant is negative. There are no known instances of standalone exotic matter in the current universe, but on the other hand, there is no much that we know about the full matter content of the universe, there is a big amount of dark energy ...

1

You are thinking of spacetime as some form of elastic fluid, and with this perspective it makes sense that if you squeeze spacetime ahead of the ship it must flow round the sides and expand again behind the ship. However this is a misleading model. Spacetime can be compressed and stretched by arbitrary amounts. For example in the FLRW metric that describes ...

1

Bending spacetime is not enough, you will also need to do it in specific ways. The simplest way of visualising the difference is to look at the Raychaudhuri equation, which describes how masses move in a gravitational field. If a gravitational field is generated using only positive energy (more precisely, obeying the weak energy condition), gravity is always ...

1

General relativity has several complications in regards to inertial frames, which I'm ignoring here because I think there's a more fundamental misunderstanding about special relativity and FTL going on here. Now using Special Relativity, we could devise a frame of reference wherein the observer would see the Star blow up before we ever left planet Earth. ...

1

This ArXiv pre-print by Brendan McMonigal actually answers this problem! He considers particles of velocities ranging from $-c$ to $+c$ (the sign denoting direction relative to the bubble, I believe) and finds that, for the most part, the particles would indeed enter & exit the bubble (receiving a velocity boost) without much trouble. The trouble, ...

1

Level 1 multiverses almost certainly exist, and any FTL drive would be able to move between them. As far as i know this includes an Alcubierre drive, assuming you could build one. So yes, an Alcuierre drive could move between level 1 universes. As far as I know the only even remotely plausible realisation of a level 2 multiverse comes from eternal ...

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