Could the Universe End by Tearing Apart Every Atom?

March 28th, 2019

PBS Member Stations rely on viewers like you. To support your local station, go to: http://to.pbs.org/DonateSPACE
↓ More info below ↓

Of all the unlikely ends of the universe, the Big Rip has to be the most spectacular. Galaxies ripped to shreds, dogs and cat first living together, then tragically separated by the infinitely accelerating expansion of space on subatomic scales. Good thing it’s not going to happen. Or is it?

Check out the new Space Time Merch Store!
https://pbsspacetime.com/

Support Space Time on Patreon
https://www.patreon.com/pbsspacetime

#bigrip #endoftheuniverse #spacetime

Learn More About Dark Energy Here:
https://www.youtube.com/playlist?list…

Hosted by Matt O’Dowd
Written by Matt O’Dowd
Graphics by Aaron Halevy
Directing by Andrew Kornhaber

The universe is expanding, and that expansion is accelerating. We don’t know what’s causing that acceleration, but that hasn’t stopped us from giving it a name. We call this unknown influence dark energy. The observed acceleration is, for the most part, nicely described with a constant density of dark energy – the same amount of this stuff in every block of space. Which means if you increase the volume you increase the overall amount of dark energy – hence accelerating expansion. Mathematically we describe a constant energy density with the cosmological constant in the equations of Einstein’s general theory of relativity. But what if dark energy is NOT constant? What if the energy density in each patch of space increases over time? In that case, the acceleration itself could be … accelerating. That would be bad.

Special thanks to our Patreon Big Bang, Quasar and Hypernova Supporters:

Big Bang:
Anton Lifshits
coolascats
David Nicklas
Fabrice Eap
Juan Benet
Justin Lloyd
Tim Davis

Quasar:
James Flowers
Mark Rosenthal
Tambe Barsbay
Vinnie Falco

Hypernova:
chuck zegar
Danton Spivey
Donal Botkin
Edmund Fokschaner
Jens Theisen
John Hofmann
Jordan Young
Joseph Salomone
kkm
Mark Heising
Matthew O’Connor

Thanks to our Patreon Gamma Ray Burst Supporters:

Alexey Eromenko
Antonio Ruiz
Bradley Jenkins
Brandon Labonte
Buruk Aregawi
Carlo Mogavero
Daniel Lyons
David Behtala
David Crane
David Schmidt
Dustan Jones
Geoffrey Short
Greg Weiss
Jack Frosch
James Hughes
James Quintero
Jinal Doshi
JJ Bagnell
John Webber
Jon Folks
Jonah
Joseph Emison
Josh Thomas
Kenneth F Leonard
Kevin Warne
Kyle Hofer
Malte Ubl
Mark Vasile
Nathan Hitchings
Nicholas Rose
Nick Virtue
Ratfeast
Richard Broman
Scott Gossett
Sigurd Ruud Frivik
Tim Crookham
Tim Stephani
Tommy Mogensen
سلطان الخليفي

And a round of applause to Andreas Nautsch.

Posted in Physics |

Is Dark Energy Getting Stronger?

March 20th, 2019

Learn More about The Great Courses Plus: http://ow.ly/wvWC30o0QYV

PBS Member Stations rely on viewers like you. To support your local station, go to: http://to.pbs.org/DonateSPACE

Check out the new Space Time Merch Store!
https://pbsspacetime.com/

Support Space Time on Patreon
https://www.patreon.com/pbsspacetime

The power of Dark Energy may be increasing as the universe ages. Subtle clues are emerging that the accepted model for the nature of dark energy and dark matter may not be all that. We saw the first such clue recently in our recent episode on the Crisis in Cosmology. Today we’re doing a Space Time Journal Club to reveal another clue. We’re looking at a new paper in Nature Astronomy, “Cosmological constraints from the Hubble diagram of quasars at high redshifts” by Risaliti and Lusso. It hints that the cosmological constant may not be so constant after all. In fact it may be increasing. If this is true, then our prediction for the future of our universe looks VERY different, and may involve the entire universe tearing itself to shreds at the subatomic level in the Big Rip.

On this edition of Space Time Journal Club we look at:
Risaliti & Lusso (2019) “Cosmological Constraints from the Hubble Diagram of Quasars at High Redshifts”
https://www.nature.com/articles/s41550-018-0657-z

#darkenergy #darkmatter #spacetime

More about The Great Courses Plus:
The Great Courses Plus is currently available to watch through a web browser to almost anyone in the world and optimized for the US, UK, and Australian markets. The Great Courses Plus is currently working to both optimize the product globally and accept credit card payments globally.

Learn More About Dark Energy Here:
https://www.youtube.com/playlist?list=PLsPUh22kYmNA6WUmOsEEi32zi_RdSUF4i

Hosted by Matt O’Dowd
Written by Matt O’Dowd
Graphics by Aaron Halevy
Directing by Andrew Kornhaber

Special thanks to our Patreon Big Bang, Quasar and Hypernova Supporters:

Big Bang:
Anton Lifshits
coolascats
David Nicklas
Fabrice Eap
Juan Benet
Justin Lloyd
Tim Davis

Quasar:
James Flowers
Mark Rosenthal
Tambe Barsbay
Vinnie Falco

Hypernova:
chuck zegar
Danton Spivey
Donal Botkin
Edmund Fokschaner
Jens Theisen
John Hofmann
Jordan Young
Joseph Salomone
kkm
Mark Heising
Matthew O’Connor

Thanks to our Patreon Gamma Ray Burst Supporters:

Posted in Physics |

Will You Travel to Space?

March 13th, 2019

PBS Member Stations rely on viewers like you. To support your local station, go to: http://to.pbs.org/DonateSPACE
↓ More info below ↓

Check out Sound Field: http://youtube.com/soundfieldpbs

Check out the new Space Time Merch Store!
https://pbsspacetime.com/

Support Space Time on Patreon
https://www.patreon.com/pbsspacetime

Thanks to Matthias Rüby for on-site camera work.
https://www.instagram.com/matthiasrueby/

The private space-race has been on for a while now. The attention has been on Space-X and Blue Origin with their reusable rockets. But there’s one private space program that’s been doing things a little differently. Richard Branson’s Virgin Galactic isn’t building rockets at all – it’s building spaceships. And I got to sit down and talk to him about it.

Tweet at us! @pbsspacetime
Facebook: facebook.com/pbsspacetime
Email us! pbsspacetime [at] gmail [dot] com
Comment on Reddit: http://www.reddit.com/r/pbsspacetime

Help translate our videos!
https://www.youtube.com/timedtext_cs

Sound Waves from the Beginning of Time
https://www.youtube.com/watch?v=PPpUx…

Hosted by Matt O’Dowd
Written by Matt O’Dowd
On-site filming by Matthias Rüby
Graphics by Aaron Halevy
Directing by Andrew Kornhaber

Amid the loud rivalry of between Elon Musk and Jeff Bezos, amid the extravagance of self-landing rockets and … other displays, Virgin Galactic achieved something no other private space company ever has – in 2014 it became the first to put an actual person in space on board its SpaceShipOne – turning its pilot into the world’s first private astronaut. And then, on February 22nd, the VSS Unity, reached space in a sub-orbital flight carrying the first-ever passenger-astronaut on a private spacecraft.

Special thanks to our Patreon Big Bang, Quasar and Hypernova Supporters:

Big Bang:
Anton Lifshits
coolascats
David Nicklas
Fabrice Eap
Juan Benet
Justin Lloyd
Tim Davis

Quasar:
James Flowers
Mark Rosenthal
Tambe Barsbay
Vinnie Falco

Hypernova:
chuck zegar
Danton Spivey
Donal Botkin
Edmund Fokschaner
Jens Theisen
John Hofmann
Jordan Young
Joseph Salomone
kkm
Mark Heising
Matthew O’Connor

Thanks to our Patreon Gamma Ray Burst Supporters:

Posted in Physics |

Why Machines That Bend Are Better

March 12th, 2019

Compliant mechanisms have lots of advantages over traditional devices. SimpliSafe is awesome security. It’s really effective, easy to use, and the price is great. Check out SimpliSafe here: https://simplisafe.com/veritasium

I visited the Compliant Mechanisms Research group at Brigham Young University and spoke to Professor Larry Howell:
https://www.compliantmechanisms.byu.edu

At the above link, you can download 3D-print files to make some of the objects in the video, plus learn more about compliant mechanisms.

What I learned about compliant mechanisms I summarize in the 8 P’s of compliant mechanisms:

1. Part count (reduced by having flexible parts instead of springs, hinges)
2. Productions processes (many, new, different enabled by compliant designs)
3. Price (reduced by fewer parts and different production processes)
4. Precise Motion (no backlash, less wear, friction)
5. Performance (no outgassing, doesn’t require lubricant)
6. Proportions (reduced through different production processes)
7. Portability (lightweight due to simpler, reduced part count designs)
8. Predictability (devices are reliable over a long period of time)

Special thanks to Patreon supporters:
Donal Botkin, James M Nicholson, Michael Krugman, Nathan Hansen, Ron Neal, Stan Presolski, Terrance Shepherd

Animation by Alan Chamberlain

Posted in Uncategorized |

The Impossibility of Perpetual Motion Machines

March 6th, 2019

You can learn more about CuriosityStream at https://curiositystream.com/spacetime

PBS Member Stations rely on viewers like you. To support your local station, go to: http://to.pbs.org/DonateSPACE

Check out the new Space Time Merch Store!
https://pbsspacetime.com/

Support Space Time on Patreon
https://www.patreon.com/pbsspacetime

See Matt in NYC at Caveat March 7th at 9pm:
https://www.caveat.nyc/event/astronaut-training-a-space-camp-game-show-for-lunatics-3-7-2019

Bad ideas come and go in physics. But there’s one bit of nonsense that is perhaps more persistent than all others: the perpetual motion machine. No working perpetual motion machine has ever been experiment verified. All break the laws of thermodynamics. In fact, we classify based on WHICH law of thermodynamics they break. We have perpetual motion machines of the first kind – they violate energy conservation – they pump more energy out than they need to keep running. This includes most of the historical devices. Then there are machines of the second kind – they’re a bit more subtle in their wrongness because break the second law of thermodynamics – extracting energy by reversing entropy. Many modern “free-energy” devices fall into this category. Now the best modern designs are by you – answers to our recent challenge question, which we’ll get to at the end. But first let’s take a look at examples of what other people came up with – this’ll be a fun little journey through some pretty terrible science.

Challenge Winners Please Email pbsspacetime@gmail.com, with your choice of product from the Merch Store (https://pbsspacetime.com/)

Connor Grey
Creepy Magician
Alex Taylor
Adrien Romeo
Epsilon Centauri
Enoae Andrei

Tweet at us! @pbsspacetime
Facebook: facebook.com/pbsspacetime
Email us! pbsspacetime [at] gmail [dot] com
Comment on Reddit: http://www.reddit.com/r/pbsspacetime

Help translate our videos!
https://www.youtube.com/timedtext_cs

Sound Waves from the Beginning of Time
https://www.youtube.com/watch?v=PPpUx…

Hosted by Matt O’Dowd
Written by Matt O’Dowd
Graphics by Kurt Ross
Directing by Andrew Kornhaber

Designing a perpetual motion machine has a very long history and became quite the craze from the middle ages through the renaissance. The first well-documented design for a perpetual motion machine was from the 12th century. Bhāskara’s wheel, named after the Indian mathematician, was embedded with tubes of mercury that would flow from back and forth as the wheel turned. Other types of over-balance wheels followed through to the Renaissance and worked on the same principle. There were also designs that employed the magical-seeming lodestones – magnets. For example, this ramp in which a ball is pulled to the top by a magnet before falling through a hole and rolling to the bottom again. Then there are the self-pumping waterwheels or self-blowing windmills.

Special thanks to our Patreon Big Bang, Quasar and Hypernova Supporters:

Big Bang:
Anton Lifshits
coolascats
David Nicklas
Fabrice Eap
Juan Benet
Justin Lloyd
Tim Davis

Quasar:
James Flowers
Mark Rosenthal
Tambe Barsbay
Vinnie Falco

Hypernova:
chuck zegar
Danton Spivey
Donal Botkin
Edmund Fokschaner
Jens Theisen
John Hofmann
Jordan Young
Joseph Salomone
kkm
Mark Heising
Matthew O’Connor

Thanks to our Patreon Gamma Ray Burst Supporters:

Posted in Physics |

Secrets of the Cosmic Microwave Background

February 20th, 2019

You can learn more about CuriosityStream at https://curiositystream.com/spacetime

PBS Member Stations rely on viewers like you. To support your local station, go to: http://to.pbs.org/DonateSPACE

Check out the new Space Time Merch Store!
https://pbsspacetime.com/

Support Space Time on Patreon
https://www.patreon.com/pbsspacetime

Hook up an old antenna to your TV and scan between channels. The static buzz you hear is mostly due to the ambient radio produced by our noisy pre-galactic civilization. But around one percent of that buzz is something very different – it’s the cosmic microwave background radiation – the remnant of the heat-glow released when the hot, dense early universe became transparent for the first time. It sound likes random static, but that buzz contains an incredible wealth of hidden information. It holds the secrets of the universe’s fiery beginning,

Tweet at us! @pbsspacetime
Facebook: facebook.com/pbsspacetime
Email us! pbsspacetime [at] gmail [dot] com
Comment on Reddit: http://www.reddit.com/r/pbsspacetime

Help translate our videos!
https://www.youtube.com/timedtext_cs

Sound Waves from the Beginning of Time
https://www.youtube.com/watch?v=PPpUxoeooZk

Hosted by Matt O’Dowd
Written by Matt O’Dowd
Graphics by Luke Maroldi
Directing by Andrew Kornhaber

It’s not surprising that scientists have spent half a century and built multiple satellites to unlock the mysteries of the cosmic microwave background. We’ve delved into its nature before – from its formation 380,000 years after the Big Bang, to its 1964 discovery by Penzias and Wilson with the Holmdel Horn Antenna, to its increasingly accurate mapping across the sky with ever-better satellites. It all culminated in this – the Planck satellite’s map of the CMB.

Special thanks to our Patreon Big Bang, Quasar and Hypernova Supporters:

Big Bang:
Anton Lifshits
coolascats
David Nicklas
Fabrice Eap
Juan Benet
Justin Lloyd
Tim Davis

Quasar:
James Flowers
Mark Rosenthal
Tambe Barsbay
Vinnie Falco

Hypernova:
chuck zegar
Danton Spivey
Donal Botkin
Edmund Fokschaner
Jens Theisen
John Hofmann
Jordan Young
Joseph Salomone
kkm
Mark Heising
Matthew O’Connor

Thanks to our Patreon Gamma Ray Burst Supporters:

Posted in Physics |

Sound Waves from the Beginning of Time

February 7th, 2019

PBS Member Stations rely on viewers like you. To support your local station, go to: http://to.pbs.org/DonateSPACE
↓ More info below ↓

You can check out Google’s Science Journal app at http://g.co/ScienceJournal

Check out the new Space Time Merch Store!
https://pbsspacetime.com/

Support Space Time on Patreon
https://www.patreon.com/pbsspacetime

Email your answers to: pbsspacetime@gmail.com
With the subject heading: Negative Mass Challenge Question

Invisible to the naked eye, our night sky is scattered with the 100s of billions of galaxies the fill the known universe. Like the stars, these galaxies form constellations – hidden patterns that echo the reverberations of matter and light in an epoch long before galaxies ever formed. These are the baryon acoustic oscillations, and they may hold the key to understanding the nature of dark energy.

Tweet at us! @pbsspacetime
Facebook: facebook.com/pbsspacetime
Email us! pbsspacetime [at] gmail [dot] com
Comment on Reddit: http://www.reddit.com/r/pbsspacetime

Help translate our videos!
https://www.youtube.com/timedtext_cs

Previous Episode: Why String Theory Is Wrong
https://youtu.be/IhpGdumLRqs

Hosted by Matt O’Dowd
Written by Matt O’Dowd
Graphics by Luke Maroldi
Directing by Andrew Kornhaber

The field of cosmology – the study of the universe on its largest scales – was once the least precise in all of astrophysics. The impossibly vast distances made accurate measurements near impossible. But as our telescopes and our techniques improved over the past few decades, things are now different. We live in the era of precision cosmology, in which we know to stunning detail the properties that govern the very birth, evolution, and end of our universe. We talked about one of those properties in a recent episode – the Hubble constant – and about a growing conflict in its measured value which hints at strange new physics. Today we’ll talk about another measurement that may help resolve this crisis: the baryon acoustic oscillations. They the fossils of the first sound waves in the universe, imprinted in the distribution of galaxies on the sky. And in these patterns we can read the expansion history of the universe.

Special thanks to our Patreon Big Bang, Quasar and Hypernova Supporters:

Big Bang:
Anton Lifshits
coolascats
David Nicklas
Fabrice Eap
Juan Benet
Justin Lloyd
Tim Davis

Quasar:
James Flowers
Mark Rosenthal
Tambe Barsbay
Vinnie Falco

Hypernova:
chuck zegar
Danton Spivey
Donal Botkin
Edmund Fokschaner
Jens Theisen
John Hofmann
Jordan Young
Joseph Salomone
kkm
Mark Heising
Matthew O’Connor

Thanks to our Patreon Gamma Ray Burst Supporters:

Posted in Physics |

Perpetual Motion From Negative Mass?

January 30th, 2019

PBS Member Stations rely on viewers like you. To support your local station, go to: http://to.pbs.org/DonateSPACE
↓ More info below ↓

Check out the new Space Time Merch Store!
https://pbsspacetime.com/

Support Space Time on Patreon
https://www.patreon.com/pbsspacetime

Email your answers to: pbsspacetime@gmail.com
With the subject heading: Negative Mass Challenge Question

Challenge question: if 1kg of apples is $5 and 2kg is $10, how much is -1kg of apples? The answer? Priceless. Because you could use negative-mass apples to build warp drives, travel in time, and construct a perpetual motion machine. In fact that last one will be today’s actual challenge question.

Tweet at us! @pbsspacetime
Facebook: facebook.com/pbsspacetime
Email us! pbsspacetime [at] gmail [dot] com
Comment on Reddit: http://www.reddit.com/r/pbsspacetime

Help translate our videos!
https://www.youtube.com/timedtext_cs

Previous Episode: Why String Theory Is Wrong
https://youtu.be/IhpGdumLRqs

Hosted by Matt O’Dowd
Written by Matt O’Dowd
Graphics by Luke Maroldi
Directing by Andrew Kornhaber

Exotic matter – matter with negative mass – has long been the pipedream of science fiction writers, futurists, and certain rather. . . optimistic researchers. It’s the key to faster than light travel because it’s the only stuff that can curve space in the right way to hold open wormholes and construct warp fields. And if you can travel faster than light you can also travel backwards in time. We’ve been over those already. And we also recently covered a very new use for negative mass: as “dark fluid”, a proposed explanation for both dark matter and dark energy. That episode really got me thinking about the subtleties of negative mass and how it should really behave gravitationally. Turns out it’s complicated, and to answer it we really have to question the very definition of mass.

Special thanks to our Patreon Big Bang, Quasar and Hypernova Supporters:

Big Bang

Anton Lifshits
CoolAsCats
David Nicklas
Fabrice Eap
Juan Benet
Justin Lloyd
TIm Davis

Quasar

James Flowers
Mark Rosenthal
Tambe Barsbay
Vinnie Falco

Hypernova

Chuck Zegar
Danton Spivey
Donal Botkin
Edmund Fokschaner
Jens Theisen
John Hofmann
Jordan Young
Joseph Salomone
kkm
Mark Heising
Matthew O’Connor

Thanks to our Patreon Gamma Ray Burst Supporters:

Alexey Eromenko
Antonio Ruiz
Bradley Jenkins
Brandon Labonte
Buruk Aregawi
Carlo Mogavero
Daniel Lyons
David Behtala
David Crane
David Schmidt
Dustan Jones
Geoffrey Short
Greg Weiss
Jack Frosch
James Hughes
James Quintero
Jinal Doshi
JJ Bagnell
John Webber
Jon Folks
Jonah
Joseph Emison
Josh Thomas
Kenneth F Leonard
Kevin Warne
Kyle Hofer
Malte Ubl
Mark Vasile
Nathan Hitchings
Nicholas Rose
Nick Virtue
Ratfeast
Richard Broman
Sammy J
Scott Gossett
Sigurd Ruud Frivik
Tim Crookham
Tim Stephani
Tommy Mogensen
سلطان الخليفي

Posted in Physics |

The Inverse Leidenfrost Effect

January 25th, 2019

Droplets levitate on a bath of liquid nitrogen and are spontaneously self-propelled. Thanks Audible! Start a 30-day trial and your first audiobook is free. Go to https://audible.com/VERITASIUM or text VERITASIUM to 500500.

Special thanks to Dr. Anaïs Gauthier
Physics of Fluids: https://pof.tnw.utwente.nl/

Self-propulsion of inverse Leidenfrost drops on a cryogenic bath
Anaïs Gauthier, Christian Diddens, Rémi Proville, Detlef Lohse, and Devaraj van der Meer
PNAS January 22, 2019 116 (4) 1174-1179; published ahead of print January 22, 2019
https://www.pnas.org/content/116/4/1174

For a detailed description of the setup:
http://www.lps.ens.fr/~adda/papiers/Langmuir2016.pdf

And self-propulsion is also seen: http://www.lps.ens.fr/~adda/papiers/InvLeidenfrost.avi

Other recent (hot) Leidenfrost experiments that might be interesting:
* Leidenfrost wheels: https://www.youtube.com/watch?v=glRGl-eYuXo
* Leidenfrost maze: https://www.youtube.com/watch?time_continue=174&v=vPZ7sx3EwUY
* Leidenfrost explosions: https://www.youtube.com/watch?v=z0sp3AjgUy4

Special thanks to Patreon supporters:
Donal Botkin, James M Nicholson, Michael Krugman, Nathan Hansen, Ron Neal, Stan Presolski, Terrance Shepherd

Thanks to Prof. Kevin McKeegan at UCLA for the liquid nitrogen

Filming by Raquel Nuno

Additional animations by Alan Chamberlain

Posted in Uncategorized |

The Crisis in Cosmology

January 24th, 2019

PBS Member Stations rely on viewers like you. To support your local station, go to: http://to.pbs.org/DonateSPACE
↓ More info below ↓

Check out the new Space Time Merch Store!
https://pbsspacetime.com/

Support Space Time on Patreon
https://www.patreon.com/pbsspacetime

The search for a single number: the hubble constant, which is the rate of expansion of our universe, has consumed astronomers for generations. Finally, two powerful and independent methods have refined its measurement to unprecedented precision. The only problem is that they don’t agree. This calls into question some of our most basic assumptions about the universe.

Tweet at us! @pbsspacetime
Facebook: facebook.com/pbsspacetime
Email us! pbsspacetime [at] gmail [dot] com
Comment on Reddit: http://www.reddit.com/r/pbsspacetime

Help translate our videos!
https://www.youtube.com/timedtext_cs

Previous Episode: Why String Theory Is Wrong
https://youtu.be/IhpGdumLRqs

Hosted by Matt O’Dowd
Written by Matt O’Dowd
Graphics by Luke Maroldi
Directing by Andrew Kornhaber

In 1929, Edwin Hubble discovered the universe. He gave us our first incontrovertible proof that there are galaxies outside the Milky Way by measuring the distances to the spiral nebulae. They were many millions of light years from us –far outside the Milky Way and so must be galaxies in their own right. Combined with the Doppler-shift velocity measurements of Vesto Slipher, Hubble revealed that the galaxies are not only receding from us, but they are receding at a rate proportional to their distance.

Special thanks to our Patreon Big Bang, Quasar and Hypernova Supporters:

Big Bang

Anton Lifshits
CoolAsCats
David Nicklas
Fabrice Eap
Juan Benet
Justin Lloyd
TIm Davis

Quasar

Dean Fuqua
James Flowers
Mark Rosenthal
Tambe Barsbay
Vinnie Falco

Hypernova

Chuck Zegar
Danton Spivey
Donal Botkin
Edmund Fokschaner
Jens Theisen
John Hofmann
Jordan Young
Joseph Salomone
Mark Heising
Matthew O’Connor

Thanks to our Patreon Gamma Ray Burst Supporters:

Alexey Eromenko
Antonio Ruiz
Bradley Jenkins
Brandon Labonte
Buruk Aregawi
Carlo Mogavero
Daniel Lyons
David Behtala
David Crane
David Schmidt
Dustan Jones
Geoffrey Short
Greg Weiss
Jack Frosch
James Hughes
James Quintero
Jinal Doshi
JJ Bagnell
John Webber
Jon Folks
Jonah
Joseph Emison
Josh Thomas
Kenneth F Leonard
Kevin Warne
Kyle Hofer
Malte Ubl
Mark Vasile
Nathan Hitchings
Nicholas Rose
Nick Virtue
Richard Broman
Sammy J
Scott Gossett
Sigurd Ruud Frivik
Tommy Mogensen
سلطان الخليفي

Posted in Physics |

On m3i: