Few of the nearly 100 routes up El Capitan at Yosemite National Park have been free climbed, meaning that ropes have been used only to catch falling climbers — not to aid their ascent. Tommy Caldwell and Kevin Jorgeson are trying to free climb the 3,000-foot Dawn Wall, a vertical sheet of mostly smooth granite that many believe is the most difficult climb in the world.

They could complete the climb by Tuesday or Wednesday.

Two world-class climbers, Alex Honnold and Beth Rodden, answer questions about the arduous journey.

Q: Why are Caldwell and Jorgeson climbing at night?

A: Honnold: Because it’s too hot in the sun. That part of the wall bakes in direct sunlight as soon as it rises. In cool conditions, they can stick to the holds better, which makes the climbing feel easier. In full heat, it feels impossible.

Q: How do Caldwell and Jorgeson belay each other when they are separated by several pitches?

A: Honnold: They have fixed lines on the wall so they can commute up and down between the particular pitches.

Q: When Caldwell climbs back to the top of Pitch 20 after helping belay Jorgeson, will he use aid on his reascent so he won’t wear himself out?

A: Rodden: I would imagine Tommy will jumar (ascend the rope, not the rock) behind Kevin to reach his high point.

Q: How is Caldwell multiple pitches past Jorgeson — don’t they have to ascend pitch by pitch together? Can Caldwell complete the climb on his own?

A: Rodden: In the ideal world, you ascend the pitches together, what climbers call swapping leads, where one person leads the pitch cleanly, then the other follows it cleanly. You would alternate who leads and follows each pitch for the entire route. Tommy and Kevin currently have ropes fixed on the route for the camera crew and to make it so they can get back and forth to their camp. In this regard, Tommy can ascend the rope to his high point; Kevin can do the same, belay him on a pitch and jumar behind him to clean the pitch. This way Kevin avoids having to grab the sharp holds, and he can rest while belaying Tommy. If Tommy did do the route by himself, Kevin would most likely follow in this way, by jumaring behind him instead of free climbing.

Q: How are anchor points established in hard-to-reach points on the wall?

A: Rodden: Some of the anchor points follow the old aid-route line; others have been established by the free climbers. Most free routes these days try to follow the no-hands-stance approach. This means that at the end of each pitch, you are able to get into a stance where you can stand without hands and set up your belay. This allows for the entire route to go free with zero points of aid. Hypothetically, if you set an anchor at a hanging belay (one where you couldn’t stand without hands), then there would be a section of the wall, however small, that you didn’t free climb, where you had to hang on the rope to move upward. After you reach the no-hands stance, you are able to hang on the belay. Some pitches are long, as in a rope length that is approximately 180 to 200 feet. Others are shorter.

Q: Who takes their gear up for them, and how?

A: Rodden: They have had their portaledges on the route for the season while they have been working on the route. They have people resupplying them with food and water during their push.

Q: Do you think that, as new generations of climbers enter Yosemite National Park, ascent times for the Dawn Wall will become the new standard for climbing excellence? Do you foresee athletes eventually speed climbing the Dawn Wall just as today’s climbers do with Yosemite’s Half Dome?

A: Honnold: I really doubt it, though it’s certainly possible. That’s sort of the case for normal El Cap free routes like Freerider. But it’s really hard to imagine climbing progressing so far that the Dawn Wall is ever easy. But someday someone will repeat it, and it will probably take less time than Tommy and Kevin are taking. We’ll see.

Q: Can you explain how Caldwell and Jorgeson will measure their success on this attempt?

A: Honnold: I think success will be both of them free climbing the wall. Anything less than a team ascent would be hugely disappointing, though I’m sure they are open to all potential scenarios. But they both hope to free the wall.

Q: How many vertical feet is the climb from the base of the cliff to the high point?

A: Honnold: It’s probably about 3,000 feet from bottom to top, though some of the climbing is horizontal, so they actually climb more than that.

Q: There is a mental strength required to complete a climb of this sort: focusing intensely for stretches amid hours of nothing, overcoming the boredom of waiting for parts to heal and staying limber, and surmounting fear and anxiety. How are Caldwell and Jorgeson dealing with the mental side of this battle with El Capitan?

A: Honnold: There is definitely mental strength involved, but maybe not as much as you think. Yes, I’m sure they’re anxious about failure and conditions and weather and all those things. But they definitely aren’t feeling any fear about the actual climbing. They’ve worked on the route for seven years -—they’re well prepared both physically and psychologically. Yes, it must be really hard for them to maintain their psyche and motivation while spending entire days resting their skin. Not being able to move at all must be tedious, and I’m sure they’re pretty tired. But they are climbing what will probably be the biggest route of their lives. I’m sure it’s not that hard to stay motivated.