Coming around to take a peek at your first chapter ...
Style/Voice: This came up in the LP earlier discussion of Suzanne Collins' The Hunger Games -- however, I'm not sure if you followed the discussion. Collins' book is written in first person present tense. Some people were mixed as to whether or not that works; however, the general consensus is that third person present tense nearly never works.
First person, present tense brings an immediacy between the reader and the characters -- not only do we get it directly from their heads, we get it as it occurs. The reason present tense works with first person is that the POV and the verb immediacy serve a purpose; therefore, the deviation from the norm is not simply distracting, but rather stylistic. What you want to avoid, however, is a present tense, third person omniscient -- because in that case, the sudden switches between POVs will simply be compounded and blurred by the present tense. Take, for example, this statement:
As they come into the room, they are too busy running to notice the upright line glowing softly in a corner.
If they are too busy running to notice, then WHO is noticing? A random narrator floating in space? If we're from the POV of these two small children, and they didn't notice the line, then we shouldn't, either. You need to choose a POV to stick with, and stick with it, because without POV consistency, the characters remain distant -- I didn't feel an emotional connection to any of them. This problem is simply compounded by the present tense, which highlights the POV discrepancies.
Just remember that with third person, the narrative distance has been already established, making the present tense frankly unnecessary. In this piece, I don't really see how the present tense serves any purpose at all, except to trip you up grammatically.
And here's the thing -- if you know you have issues with tense and grammar, it's best to first master the "basic" third person, past tense form before experimenting with others.
Characterization: This quibbling might better fit in the "Voice/Style" section, but I will include it under this subheading: dialogue.
The dialogue in this piece is stilted and unnecessarily formal. Take, for example, this line:
“Well, I am I'm scared you are going to you'll break something again. There's plenty is lots of room outside of the house, and there's no reason why you shouldn't be in the yard. It is cold only in the Kappa plane today Everywhere's warm except the Kappa plane.”
“You lost the bag, Danny.”
“No, George, I did it on purpose to slow you down.”
Real small children would never talk like this. Consider this instead:
"Danny, you dropped your bag!"
"No!" Danny wheeled around. "You fell for it."
George frowned, confused. "What do you --"
Danny smirked. "I gotta explain everything to you." He adopted a mocking voice. "I dropped it, Georgie, on purpose. To slow you down." He popped back into Kappa, and George bit his lip, irritated at his brother. However, he followed a moment later.
Because your dialogue is so stilted and colorless, you lose two important facets of narrative:
1. The opportunity to use dialogue to color characters and to bring them to life, thereby creating characters the reader will actually care about, and
2. The opportunity to use dialogue as setting, i.e. using dialect and other distinctions in dialogue in order to show us things like socioeconomic status, fantasy v. science fiction worlds, futuristic v. historical settings, etc.
As it is now, I had a really hard time telling Danny and George apart; I know one is younger and more dominant (not "dominate," by the way), but the way they talk and, more importantly, the way their point of view should color their perceptions are 100% the same. Everyone perceives the world in the same way; there are no distinctions in reaction; the story reads flat and colorless. Work on injecting some life into the story, piece by piece. Remember, this is fiction, not an instruction manual.
Okay, so now to go into specifics on how to improve:
1. Change this piece into past tense. The present tense is really detracting.
2. Work on the dialogue. Dialogue does NOT have to be 100% grammatically correct. Work on "hearing" the way people REALLY talk -- and since the vast majority of this chapter is dialogue, you want to work on injecting life into it. How to inject life? I hope that my examples help, but remember, contractions are your friends, especially when family members talk to each other (I'm v. I am). Instead of having straight dialogue for, oh, half the chapter, break the dialogue up with character actions -- tucking hair behind an ear, shifting uncomfortably, scratching a scab, etc.
3. Work on reducing wordiness. Wordiness sounds stilted and awkward; it prevents your writing from sounding natural. These will be little changes. However, they are 100% crucial in improving your craft. Take, for example:
Julie bends down to pick up some knick-knacks that have been knocked off onto the floor and hears the familiar sound of her two playful sons, Danny and George, approachingchildren getting closer.
Okay, so I added in a few words -- but that was because there's no reason NOT to have more specific information in that sentence about the children; it cuts down on wordiness later. (Like when you say "her son Danny.")
You have good ideas, and frankly, I can't really comment on the science aspects about the story. The most I can do is shake my finger at you about the craft -- that is, the way you write and shape the narrative. Take a hard, long look at this story; remember again that you're working to mimic the flows of real life, even within the machine of the story.
Hope this helps -- let me know if you have any further questions.