Karlie Kloss declares her love for longtime boyfriend Joshua Kushner, Jared's younger brother

Love is a science. Not convinced? Take it up with Karlie Kloss.

The supermodel declared her love for longtime boyfriend Joshua Kushner this week in the form of some scientific poetry: "My atoms love your atoms. It's chemistry," she wrote on Instagram, quoting poet Atticus.

"Happy birthday to my best friend and partner in crime," she continued. "The past 5 years of our adventures together have been some of the best memories of my life. I love you @joshuakushner."

Joshua is the younger brother of Jared Kushner, son-and-law and adviser to President Donald Trump. He and Ivanka Trump were already married when Karlie and Joshua began dating in 2012.

After five years together, many have speculated that marriage is on the horizon for Karlie and Joshua. While he's of typical marriage age -- 32 -- Karlie is only 24, which may be why they're taking things slow.

Karlie, a computer science activist, and Harvard Business School grad Joshua make for a not only attractive, but super-smart pair: In 2015, Joshua and Jared co-founded a tech platform that helps clients invest in real estate. The company has since raised more than $250 million in capital.

That same year, Karlie created a scholarship fund called "Kode with Klossy" benefiting girls interested in computer science and software engineering.

Although their relationship is no secret, the couple keeps a relatively low profile, only occasionally sharing photos of each other on social media. Joshua did post a faraway shot of his girlfriend in an unidentified (but exotic-looking) location on his birthday.

See photos of Karlie Kloss through the years

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Karlie Kloss through the years
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Karlie Kloss through the years
NEW YORK, NY - FEBRUARY 10: Model Karlie Kloss wearing a black coat, black turtleneck, black jogger pants outside Calvin Klein on February 10, 2017 in New York City. (Photo by Christian Vierig/Getty Images)
SYDNEY, AUSTRALIA - FEBRUARY 01: Karlie Kloss arrives ahead of the David Jones Autumn Winter 2017 Collections Launch at St Mary's Cathedral Precinct on February 1, 2017 in Sydney, Australia. (Photo by Don Arnold/WireImage)
NEW YORK, NY - JANUARY 19: Karlie Kloss is seen in Chelsea on January 19, 2017 in New York City. (Photo by Alo Ceballos/GC Images)
NEW YORK, NY - JANUARY 18: Model Karlie Kloss is seen walking in Soho on January 18, 2017 in New York City. (Photo by Raymond Hall/GC Images)
DECEMBER 11, 2016: SYDNEY, NSW - (EUROPE AND AUSTRALASIA OUT) Model Karlie Kloss poses during a photo shoot in Sydney, New South Wales. (Photo by John Appleyard/Newspix/Getty Images)
NEW YORK, NY - DECEMBER 19: Karlie Kloss seen at a film set in Manhattan on December 19, 2016 in New York City. (Photo by Robert Kamau/GC Images)
LONDON, ENGLAND - DECEMBER 05: Model Karlie Kloss poses in the winners room at The Fashion Awards 2016 at Royal Albert Hall on December 5, 2016 in London, England. (Photo by Stuart C. Wilson/Getty Images)
LONDON, ENGLAND - DECEMBER 05: Karlie Kloss attends The Fashion Awards 2016 on December 5, 2016 in London, United Kingdom. (Photo by Mike Marsland/Mike Marsland/WireImage)
LOS ANGELES, CA - NOVEMBER 20: Karlie Kloss arrives at the 2016 American Music Awards at Microsoft Theater on November 20, 2016 in Los Angeles, California. (Photo by C Flanigan/Getty Images)
NEW YORK, NY - NOVEMBER 29: Karlie Kloss is seen on November 29, 2016 in New York City. (Photo by Ignat/Bauer-Griffin/GC Images)
Model Karlie Kloss attends a Carolina Herrera party at the US embassy in Madrid, Spain, on November 14, 2016. (Photo by Oscar Gonzalez/NurPhoto via Getty Images)
NEW YORK, NY - NOVEMBER 07: Karlie Kloss at the 2016 CFDA/Vogue Fashion Fund Awards at Spring Studios on November 7, 2016 in New York City. (Photo by Gonzalo Marroquin/Patrick McMullan via Getty Images)
CAP D'ANTIBES, FRANCE - MAY 19: Karlie Kloss attends amfAR's 23rd Cinema Against AIDS Gala at Hotel du Cap-Eden-Roc on May 19, 2016 in Cap d'Antibes, France. (Photo by Dave M. Benett/amfAR16/Dave Benett/WireImage)
CANNES, FRANCE - MAY 18: Karlie Kloss attends the L'Oreal Paris Blue Obsession Party during the 69th annual Cannes Film Festival on May 18, 2016 in Cannes, France. (Photo by Jacopo Raule/FilmMagic)
CANNES, FRANCE - MAY 18: Karlie Kloss is seen at Hotel Martinez during the annual 69th Cannes Film Festival at on May 18, 2016 in Cannes, France. (Photo by Jacopo Raule/GC Images)
CANNES , FRANCE - MAY 13: Karlie Kloss attends the opening ceremony and premiere of 'La Tete Haute ('Standing Tall') during the 68th annual Cannes Film Festival on May 13, 2015 in Cannes , France. (Photo Luca Teuchmann/WireImage )
NICE, FRANCE - MAY 12: Karlie Kloss arrives at Nice Airport ahead of The 68th Annual Cannes Film Festival on May 12, 2015 in Nice, France. (Photo by Alex B. Huckle/GC Images)
LONDON, ENGLAND - DECEMBER 02: Victoria's Secret model Karlie Kloss seen backstage prior the 2014 Victoria's Secret Fashion Show on December 2, 2014 in London, England. (Photo by Dimitrios Kambouris/Getty Images for Victoria's Secret)
LONDON, ENGLAND - DECEMBER 01: Karlie Kloss attends the British Fashion Awards at London Coliseum on December 1, 2014 in London, England. (Photo by Mike Marsland/WireImage)
NEW YORK, NY - NOVEMBER 05: Model Karlie Kloss attends WSJ. Magazine 2014 Innovator Awards at Museum of Modern Art on November 5, 2014 in New York City. (Photo by Desiree Navarro/WireImage)
NEW YORK, NY - NOVEMBER 03: Karlie Kloss attends The 11th Annual CFDA/Vogue Fashion Fund Awards at Spring Studios on November 3, 2014 in New York City. (Photo by Gary Gershoff/WireImage)
NEW YORK, NY - FEBRUARY 11: Model Karlie Kloss arrives at the Oscar de la Renta fashion show during Mercedes-Benz Fashion Week Fall 2014 on February 11, 2014 in New York City. (Photo by Chelsea Lauren/Getty Images)
NEW YORK, NY - FEBRUARY 05: Model Karlie Kloss attends the 2014 amfAR New York Gala at Cipriani Wall Street on February 5, 2014 in New York City. (Photo by Mike Coppola/WireImage)
NEW YORK, NY - FEBRUARY 04: Model Karlie Kloss attends Victoria's Secret Angels Celebrate Bombshells' Day at Herald Square on February 4, 2014 in New York City. (Photo by Dimitrios Kambouris/Getty Images for Victoria's Secret)
NEW YORK, NY - OCTOBER 16: Model Karlie Kloss attends the 2013 God's Love We Deliver 2013 Golden Heart Awards Celebration at Spring Studios on October 16, 2013 in New York City. (Photo by Andrew Toth/FilmMagic)
PARIS, FRANCE - SEPTEMBER 26: Karlie Kloss seen on the streets of Paris on September 25, 2013 in Paris, France. (Photo by Timur Emek/FilmMagic)
PARIS, FRANCE - SEPTEMBER 26: Karlie Kloss A model prepares backstage prior to the Balmain show as part of the Paris Fashion Week Womenswear Spring/Summer 2014 on September 26, 2013 in Paris, France. (Photo by Antonio de Moraes Barros Filho/WireImage)
NEW YORK, NY - SEPTEMBER 09: Model Karlie Kloss attends the #DKNY25 Birthday Bash on September 9, 2013 in New York City. (Photo by Jamie McCarthy/Getty Images for DKNY)
NEW YORK, NY - SEPTEMBER 06: Karlie Kloss attends the Daily Front Row's Fashion Media Awards at Harlow on September 6, 2013 in New York City. (Photo by Michael N. Todaro/WireImage)
NEW YORK, NY - SEPTEMBER 08: Karlie Kloss seen in downtown Manhattan on September 08, 2013 in New York City. (Photo by David Krieger/Bauer-Griffin/GC Images)
NEW YORK, NY - SEPTEMBER 06: Karlie Kloss attends the Daily Front Row's Fashion Media Awards at Harlow on September 6, 2013 in New York City. (Photo by Charles Norfleet/FilmMagic)
NEW YORK, NY - SEPTEMBER 08: Model Karlie Kloss walks the runway at the Diane Von Furstenberg fashion show during Mercedes-Benz Fashion Week Spring 2014 at The Theatre at Lincoln Center on September 8, 2013 in New York City. (Photo by Frazer Harrison/Getty Images for Mercedes-Benz Fashion Week Spring 2014)
NEW YORK, NY - JUNE 03: Karlie Kloss attends 2013 CFDA Fashion Awards at Alice Tully Hall on June 3, 2013 in New York City. (Photo by Dimitrios Kambouris/WireImage)
NEW YORK, NY - MAY 30: Model Karlie Kloss attends the New York Mets vs New York Yankees game at Yankee Stadium on May 30, 2013 in New York City. (Photo by Michael Stewart/Getty Images)
CANNES, FRANCE - MAY 24: Karlie Kloss attends the premiere of 'The Immigrant' at The 66th Annual Cannes Film Festival on May 24, 2013 in Cannes, France. (Photo by Tony Barson/FilmMagic)
Karlie Kloss attends the Costume Institute Gala for the 'PUNK: Chaos to Couture' exhibition at the Metropolitan Museum of Art in New York City. ?? LAN (Photo by Lars Niki/Corbis via Getty Images)
NEW YORK, NY - FEBRUARY 07: Model/ballet dancer Karlie Kloss attends the Jay Z performance at Carnegie Hall to benefit The United Way of New York and The Shawn Carter Foundation on February 7, 2012 in New York City. (Photo by Gary Gershoff/WireImage)
NEW YORK, NY - JANUARY 10: Model Karlie Kloss attends the 2012 YMA Fashion Scholarship Fund Geoffrey Beene National Scholarship Awards dinner at the Waldorf Astoria Hotel on January 10, 2012 in New York City. (Photo by Charles Eshelman/FilmMagic)
NEW YORK - FEBRUARY 13: Karlie Kloss arrives at The 20th Anniversary of Next Models Hosted By Artistry at Marquee on February 13, 2009 in New York City. (Photo by Paul Morigi/WireImage for Next Management, LLC)
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