galaxies

[old3bob]

 

galaxies: like small grains of colorful sand or very huge bodies depending on perspective:

 

 

 

[Nungali]

like sand ... after a big explosion

 

Fascinating stuff  'mere'  sand , depending on where it comes from ;

 

 

 

 

 

 

I was out on Francios Peron peninsular  - that most western part of Oz

 

 

 

With  an Aboriginal elder , we where walking along this amazing beach with multi-coloured sand , like  a rainbow going down to the shore , I collected some different colors  and made lines of then side by side on my palm and showed them to him ; " Look at this !"

" Do you know what that is ?" he asked  and pointed to the green " Thats emerald ... "   and the pale blue  " Topaz " the dark red  "Ruby " ....   and so on  .    

 

[Nungali]

I have a big bag of  white topaz sand ; it came from very deep underground , got it from an abandoned mine ( supposedly it was going to be used for heat resistant space shuttle tiles  ? ) . Its very bright white and sparkly and surprisingly heavier than beach  or river sand .

[zerostao]

I had a galaxy all my own once

 

Spoiler

In fact, it was my first car, when I turned 16

A 1968 red two door 2 barrel 390 V8 with fm stereo Galaxy 500

 

 

At my final job the song played over the Playlist while we worked. I told a co-worker that a Galaxy 500 was my first car. She said, she thought a Galaxy 500 was a phone.

I was like,yeah, an apple used to be a fruit.

 

Edited January 8 by zerostao

[old3bob]

5 hours ago, Nungali said:

I have a big bag of  white topaz sand ; it came from very deep underground , got it from an abandoned mine ( supposedly it was going to be used for heat resistant space shuttle tiles  ? ) . Its very bright white and sparkly and surprisingly heavier than beach  or river sand .

 

cool, I've never heard of it before.

[old3bob]

off topic but I did a little bit of basic sand casting work with molten aluminum, that was neat!  Some people do very complex sand casting which is pretty amazing.

[old3bob]

they got around this problem on "Star Gate":

 

"Communication is key. That’s true on Earth and it’s true in space. But in space, you need to contend with a crucial fact of life. The speed of light is finite and distances between worlds are pretty big; between star systems they are enormous. A recent analysis envisions what it would be like to communicate with a spacecraft traveling close to the speed of light. And it is certainly not good news.

 

In their analysis, which is posted to a preprint server and is yet to be peer-reviewed, researchers David Messerschmitt, Ian Morrison, Thomas Mozdzen, and Philip Lubin envision two scenarios with a spaceship traveling close to the speed of light. This vehicle doesn’t exist (yet) but nothing in physics denies that it might be possible to build. It’s a vehicle that never goes out of thrust and moves with an acceleration of 1g, the same as the pull of gravity while we stand on the Earth.

The first scenario sees a spaceship maintaining this acceleration as it moves away from Earth. At first, the communication will work, although with a lag due to the finiteness of the speed of light, but after a while messages from Earth won’t be able to reach the spacecraft anymore. As the craft gets nearer and nearer the speed of light, it will always be a step ahead of the message. The spacecraft will then no longer be in contact with Earth.

 

• Cosmic RevolutionVoyager 1:rth's farthest spacecraft

   
• Real ScienceThe Problem with Deep Space Travel

  this is on board of the craft. An object moving close to the speed of light experiences time dilation. Its clock slows down. So for someone on board, the spaceship accelerating at 1g would take just 20 years to reach the center of the galaxy (which is 26,000 light-years away). And just 45 years to reach the edge of the visible universe (tens of billions of light-years away).

The second scenario sees the spacecraft accelerating at 1g for a while before decelerating at 1g as it approaches a destination. The communication from Earth would be affected in the same way as the first case, until during the deceleration phase when all the messages caught up with the spaceship. The destination instead could communicate with the spacecraft but the messages will tend to accumulate as the spaceship gets closer. You won’t be getting a nicely spread-out set of messages announcing their arrival long before they are very close.

 

“Interstellar spacecraft and their crews must accept highly autonomous operations, and abandon notions of maintaining operational and social interactions with those at the origin or destination throughout the mission, with the exception of a short period following launch or prior to landing,” the authors wrote in the paper.

The work looked at some classical and relativistic effects but there are even more that have not been considered that would affect the communications. The signals from a moving ship will experience a Doppler effect like an ambulance siren’s pitch changing if it’s approaching or driving away from you. So you need antennas that can detect light whose frequency will change over time. And there’s relativistic aberration: the light of a moving object is concentrated conically towards the direction of motion.

So if we ever build a spacecraft, its crew will be on their own after a while.

The paper has been posted to the preprint server arXiv.

An earlier version of this article was published in December 2023.