Analogy for Alcubeirre Warp Drive:

Every explanation of warp drive in layman terms has this sentence in it:

"The Warp Drive will contract space in thier front and expand space behind."

(I am not sure that this is literally what the alcubierre metric describes)

And then show pictures like this:

enter image description here

They also use the analogy of a surf board surfing in the sea.

This analogy of surf board makes it intuitive to understand how warp drives work.

Analogy for Lentz Soliton:

Recently I have been hearing that Eric Lentz published a paper concluding that we can have warp drive without the need of negative energy to expand spacetime.

When I search lentz soliton on google, it shows this picture:

enter image description here

It is absolutely not intuitive how the the lentz soliton works.

In the case of alcubeirre warp drive, it was intuitive that space pushes the drive from behind and pulls from the front.


I want an intuitive analogy about how the Lentz Soliton works, if there are any.


The explanation about expanding and contracting space is unfortunately an incorrect explanation of how warp drives move. Rather, it is an artefact from the times when the Alcubierre metric was proposed.

When Miguel Alcubierre's paper came out in 1994, it appeared that Alcubierre solution needed something special to move, and coincidentally Alcubierre metric has an expanded and contracted regions behind and in front of the bubble (Alcubierre paper: https://arxiv.org/abs/gr-qc/0009013, https://iopscience.iop.org/article/10.1088/0264-9381/11/5/001). So, the explanation quickly made it to the popular domain.

In 2002, Jose Natario had constructed a class of warp drives which could travel like the Alcubierre drive, but did not have any contracted or expanded regions around the bubble (Natario paper: https://arxiv.org/abs/gr-qc/0110086, https://iopscience.iop.org/article/10.1088/0264-9381/19/6/308). In other words, Natario showed that expansion and contraction have nothing to do with the motion of the warp bubble. Unfortunately, the correct explanation did not make it into the popular domain.

Erik Lentz's solution (Lentz paper: https://arxiv.org/abs/2006.07125, https://iopscience.iop.org/article/10.1088/1361-6382/abe692), just like the warp drives in the Natario class, does not need expansion and contraction to move.

In fact, the recent Bobrick paper (Bobrick paper: https://arxiv.org/abs/2102.06824, https://iopscience.iop.org/article/10.1088/1361-6382/abdf6e) shows that all physical drives move inertially, and can only accelerate by propulsion.

In summary, warp drives move because they already move, or else they need to propel, and their movement is not related to spacetime expansion or contraction.

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    $\begingroup$ Now that's the answer I needed. $\endgroup$ Jul 30 at 5:48
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    $\begingroup$ Nice answer. Could you please have a look at this additona question on how to firstly accelerate the bubble to its speed? physics.stackexchange.com/questions/656247/… $\endgroup$ Jul 30 at 7:01
  • $\begingroup$ @MartinVesely, thank you, I will be happy to take a look into it! $\endgroup$ Aug 1 at 14:53

Basically, he came up with a way to generate both the push and the pull force without needing to create negative energy, which as far as we know is impossible to do. Since energy and mass are interchangeable due to the well known equation E=mc^2, and mass can warp space time (aka it creates gravity) that in turn means that energy can also warp space time. What warp drive designs do, is contract the space time in front of them, aka they create a gravitational attraction in front of them, and expand the space time behind them, aka ANTI gravity, which since there is no negative mass and there is no way to create any significant amount of negative energy, is impossible. Lentz warp drive design is arranged in such a way that the ship is propelled forwards without needing the negative energy or reverse gravity behind it. Not all scientists are convinced of his designs validity, but he maintains his belief in it’s authenticity.

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    $\begingroup$ You didn't really gave an analogy. But still, thanks for answering a 3 months old question. $\endgroup$ Jul 14 at 5:25

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