Saturday, September 21, 2013

Is Space Moving?

These conversations took place a week ago, and if I hadn’t gotten a #$%$# cold, I would have told you about it sooner.

Last Thursday I had been bursting with enthusiasm all afternoon about the fact that the spacecraft Voyager reached interstellar space.  When I picked up Youngest Daughter after marching band practice, I did my usual Motherly Inquisition in a new way.  I asked, “Tell me something exciting.” 

YD, confused: “What do you mean?” 

Me:  “Tell me something amazing that happened to you today. For instance, I heard today that the spacecraft Voyager reached interstellar space today!  Can you top that?”

YD:  “No, I can’t top that.”

Raving about interstellar space is an excellent way to stop the flow of information from child to parent.  But I couldn’t help it.  I’m far from being a physicist or an astronomer, but I find the thought of this man-made thing flinging itself through whatever soup of anti-matter / dark matter / stardust is out there beyond the solar system to be mind-boggling.  It’s been on this road trip for 36 years.  And to think that it was leaving the heliosphere on the same day that YD was celebrating her bat mitzvah, back in August 2012!  Talk about coming of age.

At dinner on Friday night I gushed, “Don’t you think that ‘interstellar space’ is an awe-inspiring concept?  I mean, it took from 1977 until now for Voyager to get there.”

My husband burst out laughing.  Thinking of his mother at her new assisted living apartment building, he said, “That’s like when my mother says, ‘The dining room is so far away from my room that I have to leave my room at 4 o’clock to get to dinner by 5 p.m.!”

(It is true that at the Old Folks’ Home, any Old Folks’ Home, it feels like it takes 36 years for anything to happen.)

YD:  “How fast is Voyager going?

Me: I think it’s going 35,000 miles per hour!

Husband:  Relative to what?

YD and I gave him a quizzical look.

Me:  … um... relative to the space around it?

YD:  Dad.  It’s not going relative to anything.

Husband, who is not a physicist or astronomer either:  “Yes, it is.  It’s like this:  One spacecraft is going 35,000 mph in this direction, while a second space craft is going 40,000 mph toward the first spacecraft. At what time….”

Recognizing the classic ‘Two Trains Heading Toward Each Other’ Math Word Problem from, like, 5th grade, I interrupted with the answer, “Ten o’clock!”

YD:  No, Daddy!  Voyager is not moving relative to anything!  It’s just moving!

Husband:  Ah!  You are assuming that space is not moving.  But what if it is?  (raising his eyebrows knowingly.)

* * * * * * *

Maybe a speed has to be relative to something.  Maybe space is moving.  When I went to school, space was made up of nothingness, and the universe was expanding.  But these days the universe is made up of dark matter. I haven’t noticed it expanding or contracting, because I’ve been busy picking people up after marching band.  If I'm constantly moving, how can I tell if space is moving?

I was saved from answering my husband’s question, because it was time to leave for the Yom Kippur ‘Kol Nidre’ service, where we contemplated our sins, a task which, while difficult and painful, is somehow less mind-blowing than contemplating our insignificance in the cosmos.


Doug Balcom said...

I'm not an astronomer either, but I used to work for space scientists at NASA, so I picked up some basic know-how about this stuff. I believe the short answer is, Voyager 1 is moving at 38,000 mph relative to a standard sun-centered coordinate system that does not co-rotate with the planets. (The long answer, about how the axes are defined in this coordinate system, I don't know the details about, although you can probably find it somewhere on

The "is space moving?" question is more philosophical, but the "relative to what?" question is of practical importance, because the whole solar system is in turn circling the center of our galaxy at about 450,000 mph -- relative to a standard Milky Way-centered coordinate system that doesn't co-rotate with the stars in the galaxy. Meanwhile, the galaxy itself is moving relative to other galaxies...

As is true of so many important discussions, this one ultimately leads to Monty Python:

Karen (formerly kcinnova) said...

And then my brain exploded...

Cassi Renee said...

Oh, you have GOT to watch this video. Unless you already own the album :-)

Green Girl in Wisconsin said...

I've also been in awe of the Voyager--still out there--all alone--it amazes me to think of it out there plugging along.
And the old people moving to dinner cracked me up.

The Crislers said...

"Ten o'clock!" I laughed out loud. Literally.