Question:
General relativity includes a dynamical spacetime, so it is difficult to see how to identify the conserved energy and momentum. Noether's theorem allows these quantities to be determined from a Lagrangian with translation invariance, but general covariance makes translation invariance into something of a gauge symmetry. The energy and momentum derived within general relativity by Noether's presecriptions do not make a real tensor for this reason. Einstein argued that this is true for fundamental reasons, because the gravitational field could be made to vanish by a choice of coordinates. He maintained that the non-covariant energy momentum pseudotensor was in fact the best description of the energy momentum distribution in a gravitational field. This approach has been echoed by Lev Landau and Evgeny Lifshitz, and others, and has become standard. The use of non-covariant objects like pseudotensors was heavily criticized in 1917 by Erwin Schrodinger and others. After reading the above, is "Non-covariant" the correct answer to the question "Did Landau use dynamical spacetime in his theory, if not, what?"? OPTIONS:
- no
- yes

Answer:
yes

Question:
If you build a campfire, you start with a large stack of sticks and logs. As the fire burns, the stack slowly shrinks. By the end of the evening, all that is left is a small pile of ashes. What happened to the matter that you started with? Was it destroyed by the flames? It may seem that way. What do you think happened? The truth is that the same amount of matter still exists. The wood changed not only to ashes, but also to carbon dioxide, water vapor, and other gases. The gases floated off into the air, leaving behind just the ashes. Although matter was changed, it was not created or destroyed. Because the same amount of matter still exists, we can say that matter is conserved. You may wonder how it can be conserved if something is now missing? Assume you had measured the mass of the wood before you burned it. Assume you had also trapped the gases released by the burning wood and measured their mass and the mass of the ashes. What would you find? The ashes and gases combined have the same mass as the wood you started with. This example illustrates the law of conservation of mass. After reading the above, is "Matter cannot be created or destroyed" the correct answer to the question "Is any matter created when you burn wood in a campfire?"? OPTIONS:
- no
- yes

Answer:
yes

Question:
When land is cleared, habitats are lost. It may be cleared for agriculture. It may also be used for building new homes or businesses. Within the past 100 years, the amount of land used for agriculture has almost doubled. Land used for grazing cattle has more than doubled. Many wetlands have also been lost to agriculture. The U.S. has lost almost all the natural tall-grass prairies. Thee areas of tall thick grass have virtually disappeared. These areas of land had thick fertile soil. Their grasses had very deep root systems. These deep and thick roots reduced the amount of soil erosion. They also were home to many plants and animals. Prairies were wonderful places. They were home to colorful flowers, prairie dogs, and herds of bison. After reading the above, is "Animals" the correct answer to the question "What reduced the amount of soil erosion in grass?"? OPTIONS:
- no
- yes

Answer:
no

Question:
Joe's parents are farmers and they have a huge farm with cows, chickens, and ducks. Joe loves the farm and all the things he gets to play around and play on. One day, Joe's father told him not to get near a tractor that was sitting in the field. His father was worried that Joe would climb on it and hurt himself. Joe went out to the field and was feeding the horses and cows. When he was done, he saw the tractor his father told him not to get near. He knew that climbing on the tractor wouldn't hurt anything, so he did. He climbed on to the seat and sat there. Then, he pretended he was his father and pretended that he was driving the tractor. Joe's father saw him playing on the tractor and called for him. Joe heard his father calling for him and got off the tractor really fast. When he did that, he fell off and hurt his arm. Joe was in pain and his father came running to check on him and picked him up and sat him on a bench and asked him why he did that. Joe looked at his father and said, "I wanted to be like you." Joe's father gave him a hug and asked him if he wanted to ride with him on the tractor. Joe did and after he got a bandage on his arm, he and his father rode in the field on the tractor. After reading the above, is "Students" the correct answer to the question "Where did Joe live that his father told him not to play with the tractor?"? OPTIONS:
- no
- yes

Answer:
no