Can Space Time Remember?

There are cosmic events so powerful that they leave permanent marks on the fabric of the universe itself. Imagine two colossal black holes spiraling into each other, yes they send ripples in the fabric of spacetime—gravitational waves that we’ve only recently learned to sense. Ripples pass, leaving the pond … or the universe … unchanged when they’re gone. But ripples aren’t the only type of wave. There’s another type of wave that leaves a permanent mark—a memory etched in the fabric of the universe. They’re akin to gravitational tsunamis, and we’re on the verge of being able to detect them.

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Hosted by Matt O'Dowd
Written by Christopher Pollack & Matt O'Dowd
Post Production by Leonardo Scholzer, Yago Ballarini & Stephanie Faria
Directed by Andrew Kornhaber
Associate Producer: Bahar Gholipour
Executive Producer: Andrew Kornhaber
Executive in Charge for PBS: Maribel Lopez
Director of Programming for PBS: Gabrielle Ewing
Assistant Director of Programming for PBS: John Campbell

Spacetime is a production of Kornhaber Brown for PBS Digital Studios.
This program is produced by Kornhaber Brown, which is solely responsible for its content.
© 2024 PBS. All rights reserved.

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[maxmustermann]

Man when I started watching I was still in college, now im 30 and Matts beard is going grey. Hope the show keeps going strong for at least another decade

[KarelPletsStriker]

Hi, gravitational wave physicist here. Small correction on how LISA's interferometry works. It doesn't actually work like a physical interferometer because the lasers would become too faint at such long distances to do it the normal way.

Instead, it basically times the distance a photon takes to go from one detector to the other in 1 direction, and then the interferometric pattern you would normally get is reconstructed through a technique called Time Delay Interferometry (TDI)! Sadly the data analysis for LISA is quite different from the previous ground-based detectors and everyone's slightly panicking about it

[mitchellwilley]

I just wanna thank PBS Space Time for all the hard work and great videos they create. I didnt know any physics and now i have a deep understanding of how the universe works. You guys inspired me to learn physics. Thank you.

[jtgullickson]

To Matt and the team at PBS Space-time, thank you for your years of dedication and service providing us (the general public) such an in depth and resourceful insight into quantum physics, astrophysics, and all that is space and time. I've been watching since the days of calculating what planet Mario is on to jump as high as he does. Since the previous host... You enrich my life and satisfy my intense curiosity of the universe we live in. I live for this. Thanks again, JT Gullickson. From Canada. Love and Peace

[BenGrimm]

Permanent displacement in space-time suggests it’s not only elastic but also has a ‘plastic’ quality, behaving like a medium that can be permanently shaped. This also opens up the idea that space-time could have quantized properties, aligning it with quantum gravity ideas.

[faenethlorhalien]

Yes, but can it remember the 21st night of September? Love was changin' the minds of pretenders while chasin' the clouds away...

[StarkRG]

I've been looking forward to LISA since LIGO started detecting things. The precision of detecting the position of the spacecraft relative to the other two is astounding and got me thinking about something I first wondered about in my early teens, extremely-long baseline _optical_ telescopy. It's a relatively simple matter to take data from two radio telescopes on opposite sides of the Earth, do some calculations and, boom, you get the resolution of a radio telescope the size of the Earth (though with only the light-collecting ability of the area of the telescopes). You _should_ be able to do something similar with visible light, but because they're so much smaller than radio waves, you can't just collect the data and do calculations afterwards, the light has to be collected at a single location and it has to take the same amount of time to arrive. I think it's been done at smaller scales of single telescope installations, but even that's pretty difficult. I'm guessing atmospheric disturbances would make it pretty much impossible at more extreme distances. But what if there wasn't an atmosphere? You could do it on the Moon, though you'd be dealing with moon dust, and line of sight isn't all that big on the Moon anyway which would mean you'd need to add extra complexity in the form of mirrors to redirect the light over the horizon (and each one would have to be just as precisely configured as the telescopes themselves. Orbital telescopes would be best, but you'd have to be _extremely_ precise with positioning each member of the fleet relative to the detector so that the light-speed delay from each collector to the detector is exactly the same. But LISA shows that kind of precise positioning is actually possible. So imagine a small constellation of Hubbles in a polar orbit with only mirrors collecting and focusing light on a detector craft that would be orbiting perpendicular to the constellation (or maybe stuck in a Lagrange point). Orbiting them around Earth would probably be the easiest, but if we got them to orbit the sun instead, we might be able to get some _really_ high resolution imagery. I don't think we'd be able to resolve an Earth-sized planet any bigger than a single pixel, but maybe we'd get a few pixels of a Jupiter or Saturn-sized planet.

[nefdsnet]

So Dr. Serova was right and regular deformation due to FTL propulsion causes cumulative damage. Better limit cruising speeds to warp 5 until we can come up with variable geometry warp fields that will be able to prevent further damage.

[georgefowler]

Thank you Matt and PBS Space Time for being a place (in space time) that always provides coverage and release from the chaos and uncertainty of the world right now… no matter how bleak things can feel it always seems a little less dire when put in the context of the cosmos. Please keep making your great content ✨

[Turnoutburndown]

"The universe is very old, but it remembers." Why was this so ominous!? 🤣

[rodmarker]

I am 70 yrs old, I remember how as a child I was fascinated in my maths / physics lesson with "Simple Harmonic Motion" - the sine wave. I started my adult life as a geologist, but then I moved into IT, then Cyber security, it was through a lot of weed and simple harmonic motion, that shaped my life

[bananabourbonaenima]

3:00 This is not strictly true: water waves create Stokes' drift, which is a net displacement of water in the direction of the wave.

[alexandragrace]

SpaceTime is the greatest thing on YouTube and Matt is a national treasure for us Aussies. This episode was fascinating!

[chrisladd]

It's crazy that you're having this right now. I'm about to submit a paper. Thank you for everything. I will be sure to note all the helpful comments and wonderful teachings on BAO.

[petar]

Question: Where do gravitational waves "go"? Like do they chircle around the Universe? When you have a wave of water it ends up as energy that is transfered to the shore. Where do these waves (since they are form of energy) ultimately end? They can't propagate through the universe forever?

[DeathlyTired]

Made me sit up! I thought Matt said, "Thank you Raytheon for supporting PBS".
That's an interesting development I thought.
Ah! Raycon! (mental note to get ears checked)

[elliotsmith]

I would love to hear an engineering analysis of LISA. Especially the relationship between orbit, mass vs. sensitivity and resolution. What limits the orbits to where they are going to be? Can it be upgraded by adding more satellites? What exactly gets upgraded? What happens when the satellites get more massive?

[kimcosmos]

This is why they set a limit on warp speed in star trek. Stretching the space ahead and behind you makes it wrinkly and even saggy which disrupts navigation. Its one of the hazards of old age

[web]

I first learned about memory effects in spacetime in the Star Trek episode "Force of Nature" :D

[edibleapeman]

"Gravitational Spin Memory" sounds like the name of a late-90s techno/hiphop band.